Refining the Swirls

Many professionals new to the sanding side of the wood flooring trade begin on the same tool, the edger. This is common across many flooring business models. The reason seems logical; this is the most physically demanding piece of equipment we use, so why not start the new hire on it. Not only is this tool physically taxing on the back and knees, but it is also one of the most difficult tools to learn to use properly. The worst part about running the edger is the circular scratch marks it leaves behind. 

So why do we start someone with little to no experience on arguably the most difficult tool in our trade to use? The truth is, although putting the new hire on the most physically abusive tool we run helps give your back and knees a rest, it also gives the new hire an opportunity to learn what it means to leave and refine those scratches this tool places onto the floor.

This article is focused on many of the causes of swirls and ways to reduce their visibility.

ABRASIVES (EDGER PAPER)

A good friend always reminds me that the entire purpose of the edger is to turn the paper. When used properly, the edger will turn the paper in a way that will give you the desired results necessary for a premium sand job. Once you understand the intention, and proper use of the tool based on the floor you are preparing to sand, it forces you to look deeper into the type of paper you are putting on the tool. Know your paper, know its purpose, and know who is making your paper. 

SANDPAPER COMPONENTS

Sandpaper is made up of four general components: the backing, the maker adhesive coat, the abrasive mineral (or grain), and the size adhesive coat. 

• The backing is the base to which the abrasive minerals are to be bonded. In the wood flooring industry, backings typically are made up of paper, cloth, or screen mesh. The type of backing used dictates the intended usage of the abrasive. 
• The maker adhesive coat is the binding agent used to adhere the minerals to the backing. 
• The abrasive minerals or grains can be comprised of different man-made materials including aluminum oxide, silicon carbide, ceramic alumina, and zirconia alumina. Each of these minerals is used for different purposes in the sanding sequence. 
• The size adhesive coat is the final coat that holds the minerals in place. All of these adhesives are designed to withstand the high temperatures and pressure produced in the sanding process.

A common cause for swirl marks arises when the wrong abrasive is used and the proper grit sequence is not followed. It is very simple; if you skip too many grits, you will not remove the scratches left by previous grits adequately. This will leave you with swirl marks. 

Can you skip grits and still achieve a near-perfect floor? Absolutely! It is less important to contemplate whether you can, and more important to analyze how much energy is required to achieve these same results. Not just physical energy, but also the type of energy that causes unnecessary wear and tear on your edger. It takes a lot of energy to final sand with 120 grit paper to remove 50 grit scratches from the floor. Any additional force you need to place on the edger than is necessary will shorten the overall service life of the tool. The tools we use are too expensive and valuable to shorten their service life.

I am frequently asked, “so where is the recipe book for where I should start and where I should finish up?” Choosing the proper abrasive and using the appropriate grit sequence for every situation is nearly impossible to define as there are a wide variety of circumstances that may dictate many different scenarios. The abrasive grit provides information about the size of the mineral used on the paper. The grit number directly corresponds with the number and size of minerals per inch. The larger the number, the smaller the mineral. Choosing the appropriate grit and ensuing grit-sequence for the job will dictate the process to achieve the necessary results. The grit chosen for the initial sanding is determined by several conditions including existing coatings, degree of unevenness, species, and overall condition of the flooring. The grit used on this first sanding step should be the finest grit possible to remove existing coatings and flatten the floor while minimizing the scratches being placed into the flooring surface. The coarser the grit you use, the more difficult it is to remove the scratches it causes. 

THE TOOL SO THOUGHTFULLY NAMED, “THE EDGER”

Edgers, or spinners, are small circular sanding machines designed to reach the areas where big machines can’t. This includes around the perimeter of the room, in closets, on stairs, and in other small areas. These hand-held rotary-disc floor sanding machines are used to remove material, flatten the floor, and minimize scratch patterns on the flooring surface. This circular (or rotary) sanding machine is designed intentionally to move the sandpaper in a circular rotation as it comes into contact with the wood. In other words, by nature, it is supposed to leave circular swirls. So how are you supposed to alleviate swirls when the tool we use intentionally leaves them behind? An improperly operating edger can make things even worse.

EDGER COMPONENTS

The following are a few edger components that will affect how the sander leaves those swirls:

• Edger Pads – An unbalanced or bent edger pad will cause swirls and gouging. Inspect and clean edger pads before each job.
  • Worn and improperly adjusted edger pads can result in uneven sanding and swirls. 
  • An edger that has been stored upright, on its pads can cause flat spots. This often happens when setting the edger down on the floor immediately following sanding with it. The heat on the pad can enhance the rate at which it can become warped.  This can translate to vibration that will transfer to the floor, resulting in swirls. 
  • Edger pads are designed to hold one piece of edger paper at a time. Adding multiple pieces of paper will change the angle of the cut and may cause excessive heat build-up on the pad resulting in warpage, pad damage, and ultimately, swirls.
• Edger Wheels – The two wheels on the housing hold most of the machine’s weight; each is adjustable to vary the depth and angle of cut. Inspect and clean the wheels before each job, and throughout the project.
  • Wheels can attract grit, debris, adhesive residue, and wood pitch. Any build-up or contaminant on the well will force the machine out of its intended balance, resulting in swirls. 
  • The edger pad is set to hold the sandpaper disc at a slight angle to the floor. The lower the wheels are set, the steeper the pitch of the cut, and the more aggressive the sanding will be. Improperly adjusted wheels can result in gouging or swirls. 

THE EDGING PROCESS

Before beginning the edging process, it is crucial to walk the floor and make any necessary repairs. Before sanding, the floor should be vacuumed and evaluated carefully. All visible fasteners should be countersunk. The last thing you want is to hit a nail head that hasn’t been countersunk. 

The first purpose of the edger is to flatten the floor as much as possible and, in the case of a previously finished floor, to remove old finishes. The most effective way to flatten the floor with the edger is to cut across the grain. The edger should overlap into the areas where the big machine sanded in order to blend the perimeter with the field. 

As with the big machines, care should be taken to keep the machine moving to prevent gouges with the machine. Never apply pressure onto the edger to attempt getting more aggressive. This is not only hard on the machine, but also results in unsightly swirls on the floor. 

The purpose of all succeeding cuts with the edger is to refine the scratches left by preceding cuts. The most effective way to use the edger is to cut cross-grain first to flatten the floor, then move it from the wall to the field. Many professionals have different techniques that they claim will minimize the scratch left in the floor. Whether it’s the “j-hook,” the “reverse pull-back,” or a unique combination of techniques, all will be based on the same premise: clocking the edger. 

Clocking the edger is referring to the point at which the paper meets the floor, and placing that point of the pad on the floor where it aligns with the grain/floor direction. You must know your edger and where this point of contact is in order to know how to properly clock the edger. Every edger is slightly different. A properly set up edger will only make contact with the floor on a small (quarter-sized) point. Some edgers can be set to cut on the left, some on the right, and others near the center. In general, the leading edge of the paper should be cutting somewhere between 11 and 1 o’clock. Follow the manufacturer’s recommendations for setting up the edger.

Once you know the edger and where it is placing its cut onto the floor, you need to consider other factors such as keeping the floor clean. Vacuum between every cut. If you do not properly clean the floor before sanding, and between every cut, debris can create a swirl mark. It’s also possible for the debris left on the floor to clog the sandpaper, which results in inefficient sanding. 

For the final cut with the edger, use the same grit that will be used on the final sanding cut with the big machine. The final sanding processes involve the examination of visible edger and sander imperfections. These must be removed by hand prior to the final sanding stages. When using hand-held random orbital sanders or other sanding machines to remove perimeter scratches, be sure to use the same grit as was used in the final edging process. If the result is not satisfactory, the previous steps must be repeated.

THE FINAL STEPS

Tools such as buffers/rotary sanding machines, multi-disc/planetary, or oscillating machines are designed to refine the scratch patterns in the entire flooring surface to bring the scratches to an acceptable level. Grit sequence and sanding procedures will still play a key role in how the floor accepts the finish. This final sanding process blends the scratch patterns from the big machine, edgers, scrapers, and hand-held sanders. It is important to take additional time during this final step of the process. 

The final details can’t be ignored, regardless of how good of an edger you are. Many professionals have moved toward using a random orbital sander to “erase” swirls from the edger. These sanders are very effective and can produce premium results. Many professionals prefer the final refinement being done on hands and knees using scrapers and a folded over piece of paper to sand over every part of the floor touched by the edger.

Regardless of your method, or choice in tools, there are many factors that come into play when it comes to refining the scratches left behind by the sanders you’re using. The sander is designed to place a scratch in the floor. Your role is to refine that scratch. Ultimately, it’s about learning and respecting the craft of sanding. 

Check out the 2019 NWFA Installation Guidelines for more detailed sanding methods at nwfa.org. Find some quality sanding equipment manufacturers in the NWFA Industry Guide at hardwoodfloorsmag.com.

Brett Miller is the VP of Technical Standards, Training, and Certification for the National Wood Flooring Association. He can be reached at brett.miller@nwfa.org.