Love and Care of Your Finishes and Sealers – Part 1

You pay a lot for finish and sealers, so take care of them! This care includes both storage and use since either can result in the dreaded call-back and the demolition of your tidy schedule, while you burn time and money fixing the issue.

Pay attention to expiration or best-use dates. First, know how to read your product’s code; if it is not obvious, then call the manufacturer and ask how to interpret the batch/date code. Manufacturers are required to have this batch information somewhere on the jug. If the product has expired, and you are in a pinch, call and ask them if the batch is still OK to use. Most manufacturers will keep actual mini-samples, called retains, of every sealer, finish, stain, and cleaner batch throughout the mandatory one-year shelf-life date.

If a manufacturer does tell you that the batch still performs as it should, you will likely hear the caveat that it is not an “official yes.” Translation: since our retain still performs well, yours should, too. However, we know that our retains have been stored and cared for properly, but no idea how yours has actually been handled (even if you tell us that you’ve drawn a face on it and named it, taken it bowling, and kept it under your pillow).

Manufacturers often preach about storing your finish properly. There is a good reason for this: Waterbornes, in particular, are emulsions of a host of ingredients carefully added in specific steps during the manufacturing process, including resin, rheology modifiers (thickeners), defoamers, matting agents, and solvents. To keep everything where it belongs, it is important to store it at the recommended temperature and relative humidity levels.

Every time a finish is heated-cooled or cooled-heated, the process induces a driving force to unbalance the mixture. Defoaming is one property that may be affected – in extreme cases, defoamer can either “come out” (cratering upon application) or “go in” (reducing effectiveness = application bubbles that may not pop).

Remember that storing should not be forgotten once the finish leaves the distributor, your climate-controlled garage, etc., and heads off to the job site. In even moderate outside heat, the inside of a van/truck will often act like an oven, both trapping and radiating heat inward, elevating temperatures significantly above the outside/ambient temperature. Consider using a cooler to store your finishes, particularly waterbornes.

Coolers are very useful because they slow down the speed at which their contents come to ambient (whether hot or cold) temperature. Thus, a more appropriate description for a cooler would be “an enclosure that buffers the contents against outside/ambient temperature.” However, note that a cooler only slows down the process – eventually, its contents will reach ambient temperatures. Obviously, then, pulling a cooler out of an already-hot/cold garage to store finish is not going to help you; keep coolers stored close to “inside” conditions (i.e., 60-75 °F) before use.

Although it might mean leaving a six-pack behind, a cooler, when properly used, can help keep your finish “happy,” which means fewer problems for you on the job site.

What about job sites that are not sufficiently heated or cooled (i.e., some new construction scenarios)? Plan accordingly. Even if you use a cooler, if you do not plan to coat until several hours later (i.e., by which time the cooler will reach outside/ambient temperatures), consider not bringing it until later or having it delivered later. Remember, once you decide to coat, you own the results: do not coat unless job site conditions are as they should be (refer to both manufacturer recommendations and NWFA job site information). The floor and the finish should be at the same temperature at time of application.

Further, waterborne finishes are often packaged in plastic jugs which, unlike metal cans, are still somewhat air/water permeable. Elevated temperatures can increase the permeability, as a higher percentage of air/water/solvent passes through the jug. Obviously, oxygen-crosslinked (“one-component”) finishes and sealers are affected the most. However, don’t discount polyisocyanate hardener bottles, either – polyisocyanates readily react with water, losing crosslinking effectiveness. Also, added heat speeds up the loss of solvent through the hardener bottles. The end effect is a thicker (or yellowish) hardener that will not only be harder to efficiently mix into the product, but will also be less effective at crosslinking with Part A and developing properties. (Should you encounter a hardener that is either yellowish or thick, avoid using it – get a new one.)

Although it is a good idea to store all finishes out of direct sunlight, this is even more important for UV-cured finishes. Since the sun emits the entire spectrum of UV light, it is just common sense to keep UV finishes away from it; even if they are behind a window that blocks 99 percent of UV light, and even if they are in their jugs (which are often darker/denser plastics, to help block UV rays). It is best to store them in their jugs, in the cardboard carton, away from sunlight.

Finishes are not so delicate that they will crumble if storage temperatures or RHs are not ideal 100 percent of the time. However, by storing them how they should be stored, you are only stacking the odds in your favor.

Every time that you open a finish/sealer/stain jug, you essentially replace the air at the top known as the headspace. Consider that one-component finishes or sealers are usually oxygen-crosslinked. So, if you are replacing the air every time that you open the cap, that means that you are adding more oxygen for the finish to crosslink with, not to mention some solvent loss, both from the open jug and into the “new”/solvent-free headspace. Further, the less finish/more headspace there is in the jug, the greater the crosslinking effect and the greater the solvent loss to the headspace. What does this mean? More crosslinking and solvent loss will usually equate to higher viscosity, for a coat that does not flow, level, and coalesce as it should.

Oil-based finishes are not immune, either. The greater the head space, the quicker a film will form over the remaining finish. And yes, like for waterbornes, you may notice a drop in flow and leveling, faster setup, and diminished overall finish application.

Oil-based stains are probably the most-common partials in the van. There are many good reasons for this, including the need to have numerous colors available to make blends, and the possibility that only a small amount of a particular color may be needed to make a blend for a job. Worse, applying stains can mean that a can is open a lot longer than a can of oil or waterbased sealers or stains meaning more solvent loss, a lengthening of the dry time, and (if not mixed periodically) a disproportionate concentration of heavier components in the partial.

Worse, if the lid-to-can mating area is not kept clean, the cans will not properly seal, allowing more solvent to escape. Ideally, then, the best option is to predetermine the stain (or oil-based sealer/finish) amount needed for a job, and then pour the estimated extra off into smaller, “full” cans. Be sure to label these cans clearly, and always use lined cans and lids; otherwise, the driers in the stain can react with the metal of the can, resulting in a gummy product at the can-product interface, higher viscosity and longer dry times. Lined cans usually have a dark gray coating inside the cans and lids; if the metal is still shiny or metallic-gold in color, they are probably not lined. The same goes for oil-based finishes and sealers.

If you are worried about solvent loss or otherwise thick product, do not just add water or other solvents to your finishes, stains or sealers without placing a call to your manufacturer first. They can tell you if, what, how much, and when to add. Usually, since we do not actually know how the product was stored or used, you will probably only get an “unofficial” recommendation.

Be sure to have extra product on hand; do not rely on some old partial that has been opened 500 times to get you out the front door of a job. It’s best practice to use fresh finish for your final coat.

In my next article, I will address proper conditions at the job site. Until then, take care of those stains, sealers, and finishes! Do not neglect them, before, during transport, or on the job. Because, hey, what your dad always told you really is true: “If your finish ain’t happy, ain’t nobody happy.”

Ethan Erickson is a Chemist at Arboritec USA in Greenwood Village, Colorado. He can be reached at

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