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Understand What Causes Checking in Solid Wood Floors

By Michael B. Harde
October/November 2011
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photo of checks in a wood floorThe age-old misconception is that there are many conditions that can cause wood to check. The fact is that there is primarily only one. Checking in solid wood flooring has been and continues to be a prominent claims concern that all-too-often eludes proper identification, evaluation and resolution. Most folks involved with the wood flooring industry understand that checking is a condition related to moisture content changes in wood that results from drying stresses. Commonly misunderstood, however, is the fact that these stresses cannot and do not originate in wood installed within the normal environmental ranges of interior living spaces.

The Importance of Definitions

In order to properly identify checking in wood flooring, its definitions must first be understood. The following definitions were taken from the USDA Forest Products Laboratory’s General Technical Report FPL-AH-188, Dry Kiln Operators Manual, Chapter 8-Drying Defects:

Surface Checks are failures that usually occur in the wood rays on the flat-sawn faces of boards. They occur because drying stresses exceed the tensile strength of the wood perpendicular to the grain, and they are caused by tension stresses that develop in the outer part, or shell, of boards as they dry. Surface checks can also occur close to a knot, by gum pockets and mineral streaks, and in bacterially infected wood, as such wood is weaker than “normal wood.”

End Checks, like surface checks, usually occur in the wood rays but on end-grain surfaces. They also occur during the early stages of drying. End checks occur because moisture moves much faster in the longitudinal direction (along the board’s length) than in either transverse direction. Therefore, the ends of boards dry faster and shrink (or try to shrink) sooner than the rest of the lumber; the end result is that stresses develop at the ends.

Hypotheses Through the Years

Various causes have been (and continue to be) offered about why checks develop in wood flooring after installation. The following examples of commonly touted hypotheses for checking in post-installation environments provide useful insight on where we as an industry have traditionally focused:

The wood checked because …

• it was installed in an uncontrolled environment outside of the 35%-55% industry-accepted relative humidity (RH) range

• it was installed within acceptable moisture content (MC) range but dried excessively during the winter months (during seasonal periods of low RH)

• it gained moisture during the summer and swelled excessively, causing checks

• it wasn’t acclimated properly before installation (either too wet, or too dry).

Yet, as mentioned in the definitions above, the fact is that face-checking and end-checking develop as the result of drying the lumber too fast.

Looking at the Science

Numerous scientific research documents draw similar conclusions as to why and when checks develop in wood. The following excerpt taken from the USDA Forest Products Laboratory’s General Technical Report FPL-GTR-118 Drying Hardwood Lumber, Chapter 9-Operating a Dry Kiln, says:

“It is virtually impossible for lumber to check at lower MC levels (under 40% MC); the only exception is if the lumber is subjected to unusually extreme drying conditions. At lower MC levels, the shrinkage of the core exerts compression on the shell, so sufficiently large tension forces to create checking cannot develop. Surface checks may open at lower MC levels. However, the checks are not being created at low MC—they are already there and are merely re-opening.”

Therefore, end-use environments are not responsible for checks existing in hardwood used as flooring materials. Although variations in RH and temperature do influence MC and expansion and shrinkage of wood flooring and the size of the check opening, they are not extreme enough to cause the formation of checks in a piece of wood that is otherwise free of drying defects. Once wood dries below the MC saturation point of 28%-29%, it never again reaches a MC exceeding this value; in other words, the 40% MC mentioned in the previous excerpt is unattainable.

chart showing the tendency of various woods


Images of Drying Checks

Checking can manifest itself in various ways in different pieces of wood flooring. Below are some examples of problems that are all referred to as “checks” or “checking.”

photo of prefinished wood flooring
An end check is evident in this piece of prefinished wood flooring.
checks visible on face of prefinished floor
Several checks are visible on the face of this prefinished floor.
photo of checks originating from knot in wood floor
Checks can also radiate from knots.
photo of a check in a wooden board
What appears as a thin crack in this board is a check.
photo of checking appearing at the end pieces of unfinished wood flooring
Checking at the ends to various degrees can be seen in both of these pieces of unfinished wood flooring.
photo of checks in wood flooring
Checks that were barely visible when this flooring was culled from a manufacturing line became readily apparent when the flooring was exposed to low humidity.

Checks in the Installed Floor

Wood science has long identified checking as a drying defect; but it is also important to understand the mechanics behind its visible (and invisible) presence within the installed floor system.

The initial defect(s):

• Checks usually occur early in the process of drying lumber, usually above 40% MC, before being cut into flooring.

• Checks develop because the lumber surfaces get too dry too quickly (in comparison to the board’s core), and then excessive stresses develop as a result of RH that is too low.

Will checks remain open?

• Most checks, particularly those in hardwoods, close (but do not heal) in the later stages of drying. This occurs when the stresses reverse and the shell changes from tension to compression.

• For this reason, checks that close may be missed during quality control inspections during manufacturing.

Will closed checks reopen?

• Checks that are present but invisible will quite likely open to some extent during use because of normal fluctuations in RH that alternately shrink and swell the surfaces.
• Typical floor system stresses on individual and groups of boards can also prompt closed checks to open.

Site-related influence:

• With regard to hardwood flooring, there is little in the form of scientific evidence that supports checks being created by post-manufacturing interior environments. On-site, flooring will not be subjected to moisture content drops sufficient to create checking. In addition, the flooring’s surface will be nearly twice as strong when dry (compared to wet lumber’s strength), so forces required to check the wood would have to be twice as high.

Other factors:

• Variations in flexibility and brittleness in finishes impact the visibility of checks that open due to typical system stresses. Flexible finish coatings are more likely to expand and bridge the gaps, whereas more brittle finishes (especially if thin) fracture and make voids more obvious in both direct and reflective lighting conditions.

chart showing the tendency of various woods


What’s Next?

Education provides the opportunity for change. A general understanding of how and when checking develops in solid hardwood flooring is crucial if efforts to reduce the number of end-use claims are to be realized. Can checking defects be eliminated entirely during drying? No process is without flaw. The ability to dry and bring to market wood that is substantially free of checking does exist, but is the entire wood flooring industry likely to manufacture to such standards? From a practical perspective, no, probably not. However, individually, some drying operations within the industry do very well.

Supply and demand, the increase in foreign manufacture, the functional limits of the equipment used in manufacture, and fluctuating economic trends each limit the degree of quality control that can be expected prior to shipment of hardwood flooring. Our industry has determined that price and availability will be the primary criteria used in defining a products value. We have passively educated the consumer to a similar level of understanding. It is only when claims result and the potential of lost profitability is imminent that we are reminded of the importance of consistency, quality, and due diligence in defining product appearance and performance expectations to the consumer. When claims transpire, all too frequently consumers (and their living environment) are burdened with the blame, even though the checks were not caused by the consumer or by improper control of their environment

Preventative Measures

Grading standards are seldom utilized at any level in the marketing and sale of wood flooring, even though oftentimes the potential for checking is specifically qualified and quantified in these standards. Their placement on samples and within product literature would present an educational opportunity for sales staff at all levels. In addition, it would actively or passively provide the consumer with a means to acquire this valuable knowledge.
Consumers that have obtained product-specific information are less likely to voice complaints about the potential for previously disclosed and occasional defects in the finished floor. After all, wood is an imperfect and natural product. Color, grain, character, and performance variability combine to create and define each wood floor’s unique and distinctive look.

In Summary

Consideration should be given to the fact that drying defects occur, and that eliminating their existence cannot be expected nor guaranteed. In most good-quality and excellent-quality flooring mills, a very small percentage of boards will continue to be manufactured with a small level of drying defects (both visible and invisible) and will be installed. Manufacturers’ grading standards provide invaluable product-specific information that defines which characters and defects will be allowed, as well as their frequency. It is important that we make this information common knowledge for everyone’s sake.

When checks in the solid wood floor are beyond the manufactured stated limits, claims should be handled swiftly and with clear understanding on the part of all parties that the consumer was not the source for the issue.

Special thanks to Gene Wengert, emeritus professor of wood processing, University of Wisconsin-Madison, and president, The Wood Doctor’s Rx LLC, for his review of this article.

Important Points about Checks in Solid Flooring

• Checks are drying defects that occur during the lumber’s drying process.

• Checks do not originate in post-installation interior environments.

• In many instances, installers cannot and will not see closed checks before the boards are installed.

• Closed checks, which are not visible prior to or immediately following installation, can lie in wait within the installed floor, completely invisible to the eye, and may become evident over time as the floor system is subjected to reasonable and expected stresses, especially when the humidity is dropping and causing the wood to shrink.

• Checks may be allowable (in some forms) as defined in manufacturers’ grading standards specific to their products.

• Proactive sales and consumer education can significantly reduce the potential for post-installation claims relating to checking.

• If more emphasis is put on the quality of wood flooring rather than just price and availability, materials will be created to accommodate that.

Michael B. Harde is president of the International Association of Wood Flooring Professionals (IAWFP) and owner of Marlborough, N.H.-based Northeast Floor Covering Inspection and Consulting Services.

        Wood floor acclimation        Checking               


Enjoyed the article. Recently, Dr. Mitchell, well, last March in one of our classes, demonstrated to us that a 2% moisture differential from the surface of a board to the bottom can causes checks, or checking.
selva lee tucker  inspector  10/16/2011 6:37:07 PM

Dang, it posted before I finished, again, enjoyed the article. Are there any interior conditions that result in a 2% moisture differential that can cause checking? I would like to suggest if anyone can, and the classes are not expensive, attend one of Dr. Denig's kiln drying course, taught each Spring or Summer either at North Carolina State University Wood Extension Department, or in the Wood Department at Haywood Community College outside of Asheville, NC. I have been to two of them, and the great knowledge you gain for the price, well, it is great. I think anyone who calls themselves a wood floor inspector, should have this course as a requirement to attend. Anyone interested, contact me again, great article.
selva lee tucker  inspector  10/16/2011 6:41:41 PM

Mike, Thank You for your well stated, factual article. We as inspectors need factual information that can be used in our inspection observations, investigation efforts and report writing processes. I currently have three checking claims that will be written with the help of your article. Thank You again. PS. Dr. Denigs drying course was one of the best classes I have personally attended on drying wood defects.
Bill Zoetvelt  NICFI President and Flooring Inspector  10/17/2011 12:32:57 AM

Bill, I don't think you were at the last class on campus at NCSU, but, Dr. Mitchell, in his presentation, successfully demonstrated how checking can occur at only at 2% moisture differential throughout a board. The stress of the moisture gradient causes checking, which can happen in interior environments. I am sure you remember from your Kiln Class the many discussions on how important controlling stress is during drying. Now, after the moisture control class we attended we know how important it is to understand how moisture moves into and out of our homes / buildings. So, I remember years ago, there was 'abnormal checks" and 'normal checks', meaning? Anyway, Dr. Denig is thinking of helping out at the May class at NWFA this Spring. I am sure, he will be glad to teach us more. thanks! slt
lee tucker  inspector  10/17/2011 1:07:20 AM

What a nice article. It is often that people do not know that checks are CREATED during the drying process. Checks are created when the exteroir of the wood, the shell, is drying faster than the core. Drying lumber is a science and when you dry lumber to quick, checking is a typical defect that occurs. At times, you are able to "Close up" the checks later in the drying process but that does not "get rid" of the checks, they have already happened. If you have flooring that was produced from lumber that had checked during the drying process and the checks closed up at the end of the drying process, any type of rapid reduction in RH change will probaly make the checks reappear. Tricky science in drying lumber and one thing I always have said, if you don't dry it right, it doesn't matter what you do with it, it will always be a problem. Once Again, Great article and thanks for making those points for all in our business.
Tom Dean  Owner  10/17/2011 1:09:25 PM

Thank you for the article. Does the same hold true for engineered flooring? I've been running across far too many prefinished engineered floors with horrible checking. All of them are exotics with very smooth roll coat finish making it easy to spot. Many are visible right out of the box but most seem to appear a few weeks after installation. Our area has very high humidity year round, extreme sunlight that bakes floors morning and afternoon, and unusually damp subfloors. Great combo huh? Could UV curing of the finish be helping the checks open slightly?
Conrad Parducci  contractor  10/18/2011 11:48:47 AM

Excellent article; very informative.
Mike Bennett  Sales Nova USA/Ex-NWFA Inspector  10/18/2011 11:52:39 AM

Good article, what I fear is that inspector armed with this article will now be prone to decide that all checks, splits, or cracks in flooring are caused during the drying process. How can an inspector manage to tell the difference between a check that occured in the drying process and a fracture or split in a board caused by compression or stress exerted on it from a sustained increase in its MC after it was installed?
Tom Gormley  Owner  10/18/2011 1:14:28 PM

Well, there are many reasons for engineered wood to check. I can tell you now this late Spring those topics will be discussed by the NCSU professors who have been teaching wood floor inspectors the last three years about engineered wood and why it checks, warps (twisting and cupping). We were invited to use the NWFA classroom, and are in the process of reserving it now. The classes are not expensive, and the instructors are PhD wood scientist who work in wood industries troubleshooting such issues as this, and drying defects. You wil enjoy it. slt
selva lee tucker  inspector  10/18/2011 1:16:34 PM

Conrad, Thank you for your comments. Engineered flooring is a “horse of a different color”. Checking can and does occur in engineered flooring as a result of drying deficiencies (pre-manufacturing). Milling issues and product construction imbalances relative to differing coefficients of shrinkage and variables in moisture content of the plies can also result in the development of checks either prior to, or following manufacture and installation of engineered flooring. Environmental fluctuations within the structure (and other post installation factors) can also prompt the appearance of checks. These are to name but a few of the variables involved with diagnosing the cause for checking in an engineered floor. I have not personally witnessed any relationship between UV-curing of factory applied finishes and the development of checks.
Mike Harde    10/18/2011 1:30:47 PM

Tom, Good question. Lateral Compression causes crush and shear parallel with the growth rings as well as radially. It exhibits differently than a check. When viewed by a capable inspector under typical circumstances, checking should not be confused with crush.
Michael Harde  Author  10/18/2011 1:40:49 PM

Tom, Sushland, hope I spelled his name correctly, did a study published his book, about how finish applied to one side can inhibit, slow down, moisture adsorption on one side, finish applied side, causing an imbalanced throughout the board; and how long it took to reach equilibrium. So, If you like, email me and I will get you the name and publisher of the book. Enjoying the article more and more.
Lee Tucker  Inspector  10/18/2011 5:03:26 PM

Excellent educational article. We need to see more of that. Can we see an article about checks in "engineered hardwood floors"? Thanks. Paul
Paul Yau  President  10/19/2011 2:15:10 PM

Mike, Excellent article. Hoadley provides an excellent description of the stresses that occur during the initial phase of drying as wood transitions from being above Fiber Saturation Point (FSP). It is difficult to imagine a duplication of the rate of drying, differences in MC, and weakness in a piece of kiln dried wood flooring exposed to normal variance in interior RH of a properly functioning building.
Howard Brickman  Brickman Consulting  10/19/2011 5:39:19 PM

Nice article. I like articles with pictures. It's amazing how long that info has been in the wood book. But what causes checking in a stranded bamboo?
Grooving    10/19/2011 7:10:50 PM

Paul This May 31 - June 3, that will be one of the topics covered by wood scientist at a class in the NWFA classroom. Scientist who work in the industry as troubleshooters, you will like it. lee
Lee Tucker  Inspector  10/20/2011 8:17:30 PM

My intent to mention the 2% differential was to open a topic concerning "Seasonal Checks". We used to see them a lot before Factory Finish Flooring. The checks would open in the dry heating seasons, then close in the Spring and Summer months. There were even standards for length, width and depth, if I remember correctly. In Factory Finish, the hard brittle finish cracks so they are Finish Checking.
Lee Tucker  Inspector  10/23/2011 2:19:01 PM

(Continued) However, ever conscience of my ignorance, I emailed the good professor who told me I misspoke. Having admitted my past ignorance publicly right here, I said to myself, well, don't stop there. So, he reminded me that using Dr. O.S. calculations, they can "theoretically" calculate the moisture differential, in the example he used, to calculate how much it wold take to make checks in a Maple board. I have attended two of the kiln dry classes. When we pulled the lumber out to check them, using the OD method and adjusting the settings based upon our calculations, we see boards that are cupped and other issues. So, can I deduce that since those boards we saw were cupped, that all cupping claims are manufacturing? Right now, if I could hear every scream from every manufacturers' offices I would be deef. However, we know, that not to be true. . Seasonal Checks VS drying defects is something that I rarely hear anymore. Have fun
Lee Tucker  Inspector  10/23/2011 2:21:01 PM

OH yea, again, good article.
Lee Tucker  Inspector  10/23/2011 2:22:26 PM

This is exactly why I support quality manufacturers like Mirage. I was on their Mill tour last year and they are expert lumber dryers. They do it all themselves on site .Amazing process- they take their time-3- 6 months on the average depending on the species. Never had a checking probem with Mirage. YOU GET WHAT YOU PAY FOR!!!!
Dave  Retail salesperson- NJ  10/24/2011 1:50:02 PM

Just wondering... Top 4 photos, clockwise from left to right. Photo 1, is this a '' split" or a "check"? Photo 2, is that not "shake"/ "wind shake"? Photo 3, why not a "split" as it radiants lineally regardless of the grain vessels involved? Photo 4, Is this type of "star knot" not at least somewhat typical of cherry, alder and Ausy cypress etc? There should be no question regarding the bottom 2 photos but I would agree with the posit that some will insist that there is a checking problem when it may actually be truly a "shake" "split" or idiocyncracy of a knot structure.
Eric C. Jensen  Senior Territory Manager  10/25/2011 5:20:41 PM

Dave, Mirage does a fantastik job of drying and they have some of the most proffessional people to do it too... They go a step further, they have one of our automated vision system(EB3100) that looks at ALL of the boards on both ends for splits, checks, holes and other dimensional issues. They inspect 100%.
Walter Pozer  Business Development Vision Systems  10/26/2011 1:12:30 PM

It is a good article in many ways and it may not be bad journalism but it is in accurate. As for the credibility of the USFS lab, having spent time at the lab based in Madison, I can tell you that they are perhaps less than a credible source and would not myself relyon their conclusions. For example, as we all know, stair treads in some parts of the Rockies have to have the ends waxed so they don’t check on the way up the mountains. The problem is that not all checking is “bad”- in fact some of it is purposefully included. We have some products that include checking as part of the “character” of the floor. Without it we could not achieve the same look. I concur debate is constructive. However, no one should draw conclusions or absolutes from this article or the comments. . Peter
Peter Connor    11/1/2011 1:45:45 PM

This article is very misleading. Wood science is not absolute as indicated. The overall "read" is that checks are the FAULT of the manufacturer. The goal of factory drying is to reduce NATURAL checking by closely controlling the drying environment. We’ve all seen the results of drying and resulting checks in nature. A drying log has splits radiating from the center, mostly checks occurring in the NORMAL drying process. Definitions of checking are accurate. But further in the article it states "Yet, AS MENTIONED IN THE DEFINITIONS ABOVE, the fact is that face-checking and end-checking develop as the result of drying the lumber too fast." The definitions do not state that at all. That comment would lead the reader to conclude that since it's the manufacturer that dried the lumber and it was "dried to fast" all checking MUST be an error in the drying process. Checks ARE exacerbated and even caused in this manner but this statement indicates ALL checks are caused by a drying error.
neil    11/2/2011 2:49:09 PM

This article indicates that cost-cutting associated with competitive pricing pressures causes a manufacturer to ignore quality drying practices which leads to checking defects. In the end it’s the APPEARANCE of checking that creates a problem and there are many reasons it does so, albeit the checks may have been there. We must deal with the real world, no absolutes here. EX: Brazilian Cherry is supposedly more dimensionally stable than other species but it does all kinds of weird stuff out on the job. "Defect" for us indicates nearly any type of appearance or structural characteristic in wood. We often want this it's what makes it look "real". The term defect means defective to others. The consumer has no idea what a check is until they hear the word in response to a complaint. If the finding is they or site conditions caused the APPEARANCE of the check the claim may be denied. Google “checks”, this article will pop up in the top 5 and now I know it’s a manufacturing defect!
neil    11/2/2011 3:46:12 PM

Neil, I take exception to your identifying the article as “very misleading”. Let’s bring things back to a simplified and understandable level of discussion (the KISS principle). 1-Checks are DRYING DEFECTS. 2-Wood CAN be dried without formation of checks (proven science). 3-Wood DOES NOT of its own accord develop NEW checks once MC falls below 40% (feel free to present accepted documented science to the contrary if available) 4-Checking CAN be prevented. THEREFORE if present and shipped following manufacturing, they were ALLOWED End of the FACTUAL story.
Mike Harde    11/2/2011 6:17:39 PM

Your background has been as a technical director involved with wood flooring manufacturing. I understand you are now retired. Would you mind clarifying how long you have been disconnected from the industry and which manufacturers previously had employed your services and followed your technical guidance? Does your technical expertise remain in use in the form of written documentation influencing the manufacture of wood flooring products and also the handling of claims for these manufacturers? Now on with addressing the supposition and grandstanding:
Mike Harde    11/2/2011 6:20:29 PM

You stated the following - “This article indicates that cost-cutting associated with competitive pricing pressures causes a manufacturer to ignore quality drying practices which leads to checking defects. In the end it’s the APPEARANCE of checking that creates a problem and there are many reasons it does so, albeit the checks may have been there…” Your statement suggests that manufacturers know these defects exist and are hoping they won’t appear during shipping or post installation. In essence - We will manufacture, and knowingly ship product with latent defect, and hope nobody sees them until such time as the cause can be debated in consideration of supposed extreme forces to the floor caused by the living environment or structure.
Mike Harde    11/2/2011 6:22:00 PM

In your overzealousness to attack the messenger, you fail to refer to his SUMMARY. The article CLEARLY STATES – “Consideration should be given to the fact that drying defects occur, and that eliminating their existence cannot be expected nor guaranteed. In most good-quality and excellent-quality flooring mills, a very small percentage of boards will continue to be manufactured with a small level of drying defects (both visible and invisible) and will be installed. Manufacturers’ grading standards provide invaluable product-specific information that defines which characters and defects will be allowed, as well as their frequency. It is important that we make this information common knowledge for everyone’s sake. When checks in the solid wood floor are beyond the manufactured stated limits, claims should be handled swiftly and with clear understanding on the part of all parties that the consumer was not the source for the issue.”
Mike Harde    11/2/2011 6:22:39 PM

The intent of the article was to share a compilation of well researched and scientifically accurate information with people who are seldom provided it; dealers, installers, builders, consumers, and many flooring inspectors. Wood manufacturers have always understood what causes checking. The remaining stake holders have not. Education is key to the improvement of most things and this subject is no exception. There are MAJOR manufacturers who have chosen to use this article as an educational tool. I make no inference as to whether checks are, or are not acceptable in installed flooring. I only reiterate how and where they originate and that AVOIDABLE claims exposure can be significantly reduced through improved communication of this information to the parties responsible for selling or purchasing this remarkable, unique, and imperfect natural material. The consumer will be the final judge.
Mike Harde    11/2/2011 6:23:08 PM

Of course a manufacturer knows some checks exist. While they may make every effort to prevent them with the appropriate drying process and to locate them during the multiple inspection process they still know some will be there. As previously stated, checks are part of the normal drying process; it's their appearance and the cause of the appearance that is the problem. As you noted "eliminating their existence cannot be expected nor guaranteed". The fact they exist certainly does not mean that a manufacturer, as you state, will "knowingly ship a product with latent defect". That, in essence, is the total of why my response states this article is misleading. Some readers can and will surmise that manufacturers intentionally ships defective product for the variety of reasons mentioned in the article. It's unfortunate that a debate within a public forum is perceived as an attack against the "messenger". It's simply a disagreement in regards to how a reader can perceive the message.
neil    11/2/2011 7:42:07 PM

Neil- Your statement: “checks are part of the normal drying process” is very misleading. While you state a fact, it has nothing to do with this discussion relating to checking in solid wood floors. The process used in commercial drying of wood for flooring is anything but “normal”. It doesn’t even remotely resemble the manner in which a tree felled of natural cause and left untouched dries. In essence, we change everything! Why regulate these processes? To limit and reduce the amount of drying defects to a level where the wood can be successfully brought to market and sold (which differs significantly from eliminating drying defects entirely). We can talk economics here but let’s be clear that bringing a wood flooring product to market varies considerably from bringing cabinet grade lumber to market. Since drying defects are allowed, one can draw the conclusion that manufacturers do not necessarily make “every effort to prevent them”. Perhaps reasonable effort is more accurate.
Mike Harde    11/3/2011 1:11:14 AM

As relates to your statement “In the end it’s the APPEARANCE of checking that creates a problem and there are many reasons it does so, albeit the checks may have been there.” And then later in the same paragraph you state “If the finding is they or site conditions caused the APPEARANCE of the check the claim may be denied.” Although you don’t refute that the checks originated during drying, you do by inference claim to be able to determine whether a check which becomes visible in-service, did so as a result of “site conditions”. Please explain the repeatable scientific evaluation that you conduct in the field to differentiate between a check, which becomes visible as a result of typical/reasonable stresses within the in-service environment in comparison to one that became evident following excessive/unreasonable stresses. When you look at a TYPICAL check, are you Neil suggesting that you (or anyone else for that matter) can tell what conditions prompted its appearance?
Mike Harde    11/3/2011 1:11:44 AM

As an inspector, I view checking in the following manner; “A check is present in the board.” I am a collector and interpreter of facts not a crystal ball gazer. The fact that the consumer “may” (as you suggest) have caused the check to open leaves the obvious to be stated; the consumer MAY NOT have caused it to open. Until there are adequate means by which to differentiate between a check opening under typical usage and one opening as a result of excessive usage, I will not conclude who is responsible for the appearance of the defect. The same is true for environmental variables. I will only state that it is present, describe it, and identify the source for its original cause. Either you have the information needed to discern the difference between the two, or you don’t. This isn’t a debatable point, but it is one that has been argued as a viable consideration (much as you are attempting to do now) for as long as I have been involved with the flooring industry.
Mike Harde    11/3/2011 1:13:06 AM

Mike, As you are well aware I chose to contact you directly with my concerns in regards to the perception a reader may get from your article. I chose that route as I would have preferred not to have an open forum debate. I had hoped that you’d add to the comments that checking is a normal consequence of drying and is unavoidable. I’d also hoped that you would have mentioned that the very controlled and expensive process of drying is to reduce normal checking and that while checking exists there are instances in which site or consumer related issues may cause these hidden issues to appear. You did not agree, instead believing that manufacturers cause checks and should be responsible for a claim should they appear after the fact. Your further statements indicate that while checks may not be intentional the shipment of products that may have checks is tantamount to introducing product to the market with KNOWN “latent defects”. I dispute this OPINION.
neil    11/3/2011 3:36:42 AM

I feel no need to present my well known credentials. The science and case histories of published papers conflict between one writer and another. Science is often subject to interpretation and yours disagrees with mine. My industry inspector credentials are well known but they are unimportant here, the issue is who's interpretation of the "science" is accurate. Without evidence of the cause of the appearance of a check it would be impossible to blame it on the environment or user but then that's why we inspect. Where we disagree is your opinion that a check IS CAUSED by the manufacturer and, it's later appearance is the manufacturer’s responsibility and a latent defect. That opinion is misleading and detrimental to our industry. The article not only promotes excessive controversy and complaints but, unnecessarily, adds additional expense costs for inspections. This ends my portion of our debate as your tone has turned aggressive and personal which is not acceptable in this forum..
neil moss    11/3/2011 4:45:40 AM

The very best kiln operations in the world will not stand a chance against RH conditions of <25% on-site without added humidification. Hygroscopic say hello to the end-use environment. It would be dangerous to assume that conditions in the home/business do not play a role and that the origin of fault lies solely at the feet of kiln drying. Science does play an enormous role, yes, but where does common sense enter in? I hope this does not turn into "Paralysis by Over-Analysis."
David Paal, Premier Flooring Services LLC  NWFA Certified Inspector  11/3/2011 9:09:02 AM

I reviewed this article again and find it is accurate. It is possible to dry normal red oak, 4/4 and 5/4, with no checks. However, appreciate that checks in drying is formed above 50% MC. Because almost every one air dries or predryers their lumber at this MC level, and because most folks do not attempt to control drying well in these processes, checking often develops. Once a small check is formed, it is easy for it to grow large, even at low MCs. Also, a surface check is often invisible in dry wood, but it will reopen when the wood is exposed to very dry conditions. An important point is that dry wood is twice as strong as wet wood. Also, in drying the MC change at the surface in air drying is roughly 30% MC to 12% MC. This change or differential of 18% is huge compared to a several percent change in an installed floor.
Gene Wengert-WoodDoc  Wood Technologist  11/3/2011 11:25:58 AM

The Facts: Hardwood Floors check in Las Vegas in the summer where there is 5% RH; in North Dakota in the winter where there is 15% RH; and in Indianapolis in the winter where we see 25% RH routinely. The Presumed: The manufacturer released 1st quality, properly kiln dried, properly graded, properly finished, and properly QC'd product.
David Paal, Premier Flooring Services LLC  NWFA Certified Inspector  11/3/2011 11:26:01 AM

The Truth: 1) Did the distributor and/or flooring contractor employ the proper climate controlled conditions in warehousing while the wood sat for 3-6 months before sale? And what about the importers since I've never known containers to use climate control. 2) Did the end-user assume responsibility and maintain ambient conditions correctly per recommended guidelines? 3) If the indoor humidification in all of the cities listed was maintained at 40-45% year round, there would more than likely be no checking even if the kiln drying was or wasn't perfect. 4) Left to the laws of nature, and with no help from maintained proper humidification levels, hardwood checks if it gets too dry. Go look at a tree stump.
David Paal, Premier Flooring Services LLC  NWFA Certified Inspector  11/3/2011 11:27:02 AM

Of course, a floor could get wet from rain just before installation and a heater used to quickly dry the floor, so there are a few instances (unusual) when dry wood can have huge stress levels. Even so, dry wood is so strong, that it will take more than a little shrinkage in a 2" wide piece of wood to develop a new crack. Of course, if the flooring is 12" wide and there is a large and rapid MC difference, then we might indeed see enuf stress. A rule of thumb is that it takes 4% MC change to create a 1% size change in width or thickness. It is interesting when I deal with flooring cracks how often there will be finish inside the crack. Obviously, the crack was there before finishing. When talking about MC, it is well to remember that we could talk about the average for a piece, or we could talk about what happens at a specific location, like the surface.
Gene Wengert-WoodDoc  Wood Technologist  11/3/2011 11:27:02 AM

The Conclusion: 1) Mike's article is good, no doubt; however it is not an Industry Standard to be used in report writing. 2) Known science is subject to the natural world from where it originated. It's always changing and never absolute; key word is never. Example: cancer research. 3) Hygroscopic changes in wood are impacted by the natural changes to the environments they function within. We are to presume nothing more. 4) Properly conducted kiln drying does not equal distributor/contractor/end-user exoneration of responsibility if checking occurs. Class dismissed. It's lunch time.
David Paal, Premier Flooring Services LLC  NWFA Certified Inspector  11/3/2011 11:27:34 AM

We sometimes deal with wood that is not as strong as normal. This weaker wood can be caused by bacteria in the tree (which also smells and also creates shake, which is a crack running with the growth rings and not across) or by the formation of tension wood in the tree (which also causes fuzzing when machining and low weight). Weaker wood is much more prone to checking. Weaker wood is hard to identify in lumber until we see checking under otherwise safe or normal conditions. To get around checking, some furniture and cabinet manufacturers will humidify their plant. The humidity keeps the surface fibers. Slightly swollen, so to speak, so any checks are so tightly closed that they are invisible. Of course, when the customer exposes to wood to the normal dry wintertime humidity, there will be some drying and shrinkage at the surface which will reopen the cracks.
Gene Wengert-WoodDoc  Wood Technologist  11/3/2011 11:29:10 AM

Those of us who are older will recall when floors were finished with varnish and the varnish was actually quite flexible, so small checks were not an issue...the finish did not crack easily. Today's finishes are thinner, provide much less of a barrier to moisture vapor movement, and are more brittle, so opening of checks is indeed more of an issue now. The checking that we see in Nevada or ND or in the wintertime on standard strip flooring is either an existing check that has reopened or is abnormally weak wood (rare). As the article and my comments stated, wood, when dry, is so much stronger and also the moisture change is actually quite small (unless the wood was mishandled prior to installation). Stated another way, if a small moisture change can get dry strong wood to crack, it would be next to impossible to dry wood without a tremendous amount of checking, as wet wood is weaker and the MC change and shrinkage is so much larger.
Gene Wengert-WoodDoc  Wood Technologist  11/3/2011 11:34:14 AM

Unless the wood flooring has been mishandled after manufacturing, any checking that the consumer sees is a result of checks that developed during drying. Here are the facts. In drying, air drying of wetter wood has a humidity difference between the surface, which is at 100% RH, and the air which is 65% RH (or even 30% RH or much lower on a warm, dry day). The shrinkage between wet and 65% RH is more than 2/3 (maybe 3/4) of the total shrinkage in wood. Wet wood is about half as strong as dry wood. Even so, wet wood can withstand this dry RH most of the time without checking. Humidity changes in a home will be about 20% RH to 60% RH, which is under 20% of the total shrinkage in wood. Dry wood is stronger Lumber does not have a finish on it which slows moisture changes.
Gene Wengert-WoodDoc  Wood Technology  11/3/2011 11:48:01 AM

Dr. Gene, you stated above that, "any checking that the consumer sees is a result of checks that developed during drying." Are we to conclude here that any checks seen by a consumer, could not have originated without improper kiln drying first? My question really becomes is it possible for checks to manifest in dry RH climates even if kiln drying is perfectly performed in the beginning? Without proper indoor humidification, I conclude it is. That is the debate here as I see it. Thanks for your reply.
David Paal, Premier Flooring Services LLC  NWFA Certified Inspector  11/3/2011 12:05:42 PM

The small amount of shrinkage in very dry climates and the strength of such dry wood mean that UNLESS THE WOOD HAS BEEN MISHANDLED AFTER MANUFACTURING, that checks are a result of "improper" drying. Sometimes drying is proper but the wood was unusual, etc.
Gene Wengert  Wood Technologist  11/3/2011 1:09:27 PM

"UNLESS THE WOOD HAS BEEN MISHANDLED AFTER MANUFACTURING" now opens up the possibility for numerous variables to enter the equation that are not the responsibility of the manufacturer. That language appears to me as a disclaimer, and technically speaking, it qualifies as a disclaimer. All of us here know what arid environments are capable of. For many years, a premium domestic U.S. manufacturer did not sell hickory in dry arid climates like the northern Midwest or desert Southwest for fear of checking on-site in dry uncontrolled conditions. Their reasoning was well founded. Their manufacturing facilities are amongst the finest in the world.
David Paal, Premier Flooring Services LLC  NWFA Certified Inspector  11/3/2011 3:13:16 PM

This was an educational article. The extensive comments have added interesting perspective. I install in the high desert of the southwest, a mile above sea level. As a practical matter, the cost of repairing the occasional check or split is minimal. It offers a great opportunity to build and solidify customer relationships which makes better biz sense than calling in an inspector and determining responsible party. In the lumber industry we call checks, streaks and knots defects, our customers call them character. Communicate expectations early and avoid making this anything more than a very interesting theoretical wood properties discussion.
kevin  wood floor installer  11/3/2011 4:05:07 PM

You are correct Kevin; you control the debate by communicating the correct expectation beforehand with your end-user. Well done.
David Paal, Premier Flooring Services LLC  NWFA Certified Inspector  11/3/2011 4:53:23 PM

A dry environment is not mishandling. Rewetting is.
Gene Wengert-WoodDoc  Wood technologist  11/3/2011 11:34:44 PM

For the top pieces in a bundle on the top of a load in a truck parked in a hot, sunny location (temperatures can easily reach 150 F inside at the top with humidities close to zero due to the heat) is mishandling. Incidentally, it takes about 25 pints of water to change the MC of 1000 sq ft of oak strip flooring by 1%MC. The MC of flooring in a tight container will not change in shipping as you cannot easily (unless there is a hole in the roof) get the large amounts of water into or out of the container. Similarly for plastic wrapped products. Also, when checking the MC of uninstalled flooring with a pin type meter with insulated needles, the core MC represents the MC of the lumber when it left the kiln for many months, as the core MC just doesn't change easily or quickly.
Gene Wengert  wood Technologist  11/4/2011 1:46:20 PM

Those who mfg wood flooring must compete, including drying lbr efficiently. The 3-6 month process observed at Mirage is not unique. Mirage is nice stuff, and historically priced accordingly - as stated you get what you pay for. As noted occasionally thruout these comments, the practical solution is often good communication. Nobody wants a bad surprise; better communication can often preclude one. Nothing is perfect, but the natural characteristics of wood flooring are both a challenge and, simultaneously, the source of much of our success.
Tony Miraldi  Somerset Tech Svcs  11/4/2011 2:02:30 PM

Let me throw out a customer perspective. I have this problem in my newly built house delivered with a prefinished plank solid product. It was distressing, because the checks appeared as splits in the wood and we have many of them.   First, the installer inspected and said the checks were normal, was not an installation issue, and blamed it on an (unidentified) on-site moisture issue. Then the manufacturer’s certified inspector said that checks are not considered a defect by the flooring industry and was acceptable.   I had to independently hire and pay for a CWFI to get any validation that this wasn’t all my (the customers) fault. My take away from this excellent article, despite my recent experience, is not that it is ALL the manufacturer’s fault. I completely agree that more communication would help, but more education for manufacturers, installers & inspectors is clearly needed as well. I am disappointed at how I was treated by professional and respected installers and inspectors.
JK  Consumer  11/4/2011 3:28:01 PM

Dr. Wengert, A question based on the last sentence of your latest comment; A pallet of 3/4''x 4'' flat sawn red oak is milled at 8-9% core mc. Then stored at 70 degrees 20-25%rh, bundles stickered. ballpark how many months to change core by 1-2%? same question for r&q red oak of = dimension. Thank you for volunteering your knowledge.
kevin  wood floor installer  11/4/2011 3:39:34 PM

I would guess that two months minimum with some small amount of air movement. Rift and quarter would be 15% longer. Smaller bundles go faster than large.
Gene Wengert-WoodDoc  wood Technologist consultant  11/4/2011 10:59:07 PM

OMG the wood doctor Gene is here! Love your video Gene!
grooving    11/4/2011 10:59:51 PM

I see a lot of comments here so I want to qualify my "experience". My limited experience in drying wood is extremely limited to two classes, taught by experts in this field. Having taken the two classes, my "limited experience" taught me, I don't know jack. I know that Neil has probably sent a good deal of time with Kiln Dry operators. My question is how many commenting here have actual hand on / involvement drying hardwood lumber? I will never claim to be an expert in this field, having been shown how much I don't know. Sometimes, education does not make a person an expert, but instead teaches the person how much they don't know.
Lee Tucker  Inspector  11/7/2011 9:37:50 PM

Post continued: So, as I said, Neil in his past job most likely has worked with kiln dry operators but how many of us have experience drying hardwood lumber? So, what I am going to suggest is that some of you attend one of the classes. I can make arrangements for inspectors or other interested parties to attend an actual class with real kiln dry operators, who do it "for real". And then, you too can be ignorant like me.
Lee Tucker  Inspector  11/7/2011 9:40:59 PM

Mike, your article was very informative and well presented. I have been "encouraged" by your willingness respond forcefully to criticism of your educational effort. I have used this forum and others for some time to voice my opinion that the manufacturer's perspective is given excessive weight in the dissemination of information to other players in this wood flooring game. Distributors, retailers, contractors, consumers, and independent inspectors-for certain, need to have information such as is presented in this article; information that does not have a manufacturer's filter placed upon it. As an extra note- I was able to attend the 4 day Moisture In The Home Workshop in September, organized by Lee Tucker and sponsored by his Inspectors Guild. Great information was presented there as well, by Howard Brickman and North Carolina State University professors.
Joe Clarke  Flooring contractor & Inspector  11/8/2011 10:26:21 PM

Thank you Joe, I think the classes present information that is fair and balanced. They call it as it is. If it is manufacturing, then that is what it is. If it is just the nature of wood, then that is what it is. Guys, these are wood professors who have worked in the industry, not classroom ivory tower guys. They love the wood industry! Joe, So many said just what you did. I don't teach, I am not qualified. Some manufacturers like the classes, the honest truthful ones. I hope many of you will attend this next one. It is going to be, very interesting in some of the subject taught.
lee tucker  inspector  11/8/2011 11:13:24 PM

Good article. Fact and science based. Appreciate reference to the Wood Book to prove article accurate. Thank you
Ray Darrah  National Inspection Service Technical Director  11/9/2011 9:49:26 AM

This has been a great discussion to Mike’s article and we must allow the facts to be heard. I too would have to agree checking develops in the early stages of the drying process however with modern drying technology pushes lumber yields up, not down. It has been stated in the comments this article has been very misleading which I would also have to agree. As Peter Connor stated, checks are part of the grade, not classified as a defect but rather character to the grade itself and the grade could not be obtained without checks. As we look at the market today how many clear grades sold vs. builders, rustic or character grades? We must admit this stated defect is not a defect after all but rather common character used by most manufactures today because of supply and demand.
Roy Reichow  National Wood Floor Consultants  11/11/2011 12:27:38 PM

I believe this article has also been targeted towards pre-finished solids vs. un-finished solids. One rarely hears complaints from the floor finisher regarding checking, cracking yes, but rarely checking. When the site finished floor experiences normal seasonal change (20%RH) most site applied finishes can withstand the stress and have no ill affects on checks. While pre-finished multi-layer aluminum oxide finishes or equivalent are more brittle and will show white to sliver shadowing pronouncing the check once seasonal change (maybe .005”) has taken place, the star knot in the article proves this case. An oil finish system, the check (character mark) would appear to the end-users eye the same year round yet the same check with aluminum oxide finish or any other brittle type finish will have silver shadowing. So what is the real concern here the grade (including kiln checks) or the compromised finish caught the end-users eye?
Roy Reichow  National Wood Floor Consultants  11/11/2011 12:30:51 PM

Inspectors cannot classify checking as a defect unless they have supporting data from the manufacture that checking is not part of their grading standard. For the low cost inspectors this may get exceptionally frustrating when one might spend an one, two or more hours just getting through to the manufactures technical director just to get this answer for the report. Otherwise the inspector cannot make the “defect” statement even if wood science proves the character marks (checks) happened during the drying process. I suggest manufactures only sell "Clear" grades which don't allow checks, sell only oil type finishes and this would make it clear for inspectors where the check defect begins.... it sure would save on inspections because we wouldn't sell much flooring due to price point of other floor coverings. Point is we can not change change the flooring trend but we can change how checks are looked upon through different lenses.
Roy Reichow  National Wood Floor Consultants  11/11/2011 12:44:49 PM

The discussion thus far has been very spirited, but there has yet to be a single instance where “new” factual information (supported by scientific documentation) has been posted. Many opinions, but NO NEW FACTS. We have seemingly moved past the misnomer that checking can occur within the in-service environment (no more blaming consumers for checks as the result of out of range RH levels or maintenance abuse). Thank you Dr. Wengert for helping us understand these factors more clearly and specifically.
Mike Harde    11/12/2011 1:58:35 AM

Roy- In regards to checks you write “We must admit this stated defect is not a defect after all but rather common character used by most manufactures today because of supply and demand.” The word “common” imparts that it is knowledge shared by all. It seems extraordinarily contradictory to use the word “common” and then state later in your comments about inspectors plights in finding this information “…exceptionally frustrating when one might spend an one, two or more hours just getting through to the manufactures technical director just to get this answer for the report”. If it takes a specially trained wood flooring inspector 1-2 hours to gather “common” information; it ain’t too common!
Mike Harde    11/12/2011 2:01:23 AM

Perhaps in the future through improved education and communication to stake holders and consumers checks can become “character marks” but at present they are drying defects. Written grading information qualifying the existence of checks provides a means of determining whether the in-service floor meets the standard. The defect may, or may not be within range. Credible inspectors can define checks in no other way.
Mike Harde    11/12/2011 2:01:57 AM

I have never seen a single instance where samples, brochures or other manufacturer disseminated information about the acceptability of checks has been made available to the public or retail sector. Perhaps I am remiss. Can you specifically suggest a single manufacturers sales brochure or sample where this occurs? Can you imagine a retailer or consumers success rate in proactively pursuing this information on their own? I am a huge advocate for education. It is the primary reason I felt compelled to write this article and i believe it to be key in dealing with product issues.
Mike Harde    11/12/2011 2:08:55 AM

You strike me as an individual who loves to debate especially when you think you are right! It's been agreed by ALL checks happen during the drying process, period!!! But what you failed to leave out in the article is prefinished vs unfinished ratio, or finish types and which have the highest ratio of claims that you refer to? Therefore this article is incomplete as to your statement and very misleading to many. Secondly a check can be closed at time of manufacturer and install yet reopen when RH levels drop below 35% relating to environmental changes, not manufacture. Far as "Common" I believe it is the most popular grade today whether it's 1 or 3 common or proprietary grade somewhere in between which also you failed to disclose within the article. These grades do have kiln checks accepted which are now classified as character marks to obtain grade. You also failed to detail hard finishes which show finish checking when check moves slightly with normal RH fluctuations.
Roy Reichow  National Wood Floor Consultants  11/14/2011 12:01:56 PM

This debate is one of the best I have read in a while. I have brought this article to the attention of the NWFA BOD as a misleading article that will in my opinion, as well as many others, cost the manufactures a lot of money in claims. I say this because there are so many so called inspectors and probably some that do know more than the average inspector, that will use this article published in HFM as gospel. Anything that resembles a crack, including shake, will be called a CHECK as is a manufacturing defect. The absolute of this article as printed is a problem.
Rick Jones    11/18/2011 10:36:15 AM

Continued Roy states very well in my opinion much that needed to be added was stated. Neil probably knows more than most of us combined will know and I say this having debated back an fort with him for maybe 30 years. David also makes valid points and is knowledgeable. Having said these things, I will also say, "Most all of us know what is done in the lab and what really makes in the field is not the same. Don't get me wrong, Science is a remarkable tool and device to provide much needed understanding about how everything works but it is also changing because a theory is proven to be wrong and a new one written. The absolutes used in this article in my opinion again, is misleading and I feel our professors here are spending too much time to make themselves RIGHT, when the article, not the Science, is flawed and left wanting of more. This is my 2 cents worth and I don't intend on any future debate with a professor on theory.
Rick Jones    11/18/2011 10:44:40 AM

A few comments for the record--A specific definition for CHECK was offered in multiple industry documents over a long period of time. That definition was: "CHECK A lengthwise separation of the wood that usually extends across the rings of annual growth and commonly results from stress set up in wood during air or kiln drying." This definition was included in the revised 2002 version of NWFA INSTALLATION GUIDELINES, the 1996 version of the training manual offered by NWFA's own Don Conner while he was technical and training director at Harris Tarkett, and in the information manual provided at the 1996 NOFMA/NWFA/MFMA school in Memphis with Micky Moore as lead instructor. The 2007 version of the NWFA INSTALLATION GUIDELINES does not include "and commonly results from stress set up in wood during air or kiln drying" portion of the definition. Guess they were running out of room in the glossary section? NOT!!!
Joe Clarke  Wood Flooring Contractor- Inspector  11/23/2011 10:34:01 PM

continued--- Mike's article to me seems about as complete as one can design a magazine article. This article is about CHECKING IN SOLID WOOD not finish checking or alligator finish. Maybe he will decide to give a shout out on that subject next. (I'll bet the aluminum oxide factory finish guys can't wait on that information to publish.) His comments,copied below, seem to properly address the finish issue for this article. "OTHER FACTORS • Variations in flexibility and brittleness in finishes impact the visibility of checks that open due to typical system stresses. Flexible finish coatings are more likely to expand and bridge the gaps, whereas more brittle finishes (especially if thin) fracture and make voids more obvious in both direct and reflective lighting conditions." Rick, I have a deep respect for your opinion,but, your manufacturer hat is glowing bright in your comments. If the manufacturer community was educating the consumer properly, instead of blaming them------
Joe clarke  Wood Flooring Contractor- Inspector  11/23/2011 11:20:34 PM

continued---The NWFA should be about promoting wood flooring and associated products. That is a very large hat to wear. Mike's article is summary of well researched and LONG ACCEPTED information- Information accepted and published by definition for a CHECK by NWFA, by NOFMA, and by Southern Pine Inspection Bureau. I cannot see how that can be construed as misleading to anyone. The inability to put all information about all facets of an issue into a magazine article, does not make the information presented misleading. My opinion is that if the NWFA BOD decides to act in some manner to discredit the article, then a bias toward manufacturing will be demonstrated that in the long term will erode the credibility of NWFA as a honest broker of information. If manufacturing has to make some changes in the way they do business and disseminate information-then so be it.
Joe Clarke  Wood Flooring Contractor- Inspector  11/24/2011 1:10:41 AM

This is a great discussion, thank you. I believe checks are simply a grading issue, not related to Defects. Checks are allowed, per NOFMA Standards. The difference is how many and what size depending on the grade of the wood. Am I correct or does this matter?
Ray Darrah  Technical Director  3/5/2012 2:50:41 PM

How doi you grade checks if you cannot see them Ray?
grooving  owner  4/11/2012 9:30:22 PM

Annually there are thousands of finished wood flooring systems subjected directly to bulk water damage. Usually the extent is a portion of the entire flooring system, but not always as I have seen entire houses flooded for hours, days and weeks. Excess moisture naturally results in an elevated, uneven MC causing stress. The on location water damage mitigation industry has come up with methods of removing (in most cases, but not all) excess moisture from subfloors and finished flooring. We sometimes see MC in parts of flooring beyond FSP. Drying techniques over the years have brought it down to (where possible where there is a crawlspace or basement) drying the subfloor with heat and dehumidification and separately drying the finished floor above. Where we see some cracking, hour glassing and checking sometimes occurs when too much energy is focused on the flooring. The forces are too much heat (often 120f and hotter) and too low an rH through both of heat and reduced vapor pressure in the air - different than reducing rH through heat. This heat and lower vapor pressure air is induced down through the boards along the sides, butt ends and the expansion area around the room through high vacuum pressures exerted on the boards. Air is moved through the interstitial spaces in the tongue and groove area and the flute system. If too hot and or too dry, the boards can develop a crust and a seriously high gradient from wet to dry sections on the boards can fatally damage some finished floors - even those less prone to stress damage during the kiln drying process. The goal of the restorer should be to eliminate cupping without over-drying. This is like horseshoes, get close, but do not unrealistically attempt to get all portions of all boards down to a typical (for that structure) MC. It can't happen uniformly. The restorer and refinisher should then wait 30-180 days before any sanding and refinishing to avoid crowning. Too often, refinishing is attempted too soon.
Ernie Storrer  President / Technical Director  4/17/2012 2:30:27 PM

Latent defects are those problems that pop up after installation. However; Grading is still an issue and the percentage of the floor affected does matter.
Ray Darrah  3/12/2013 10:08:14 PM

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