Eliminate Finish Failures with Finishing Systems 10/9/2012 10:00:00 AM
Finish failures are often the result of using the wrong combination of finishes or using the finishes incorrectly. Finish suppliers recommend finishing systems comprised of finishes that are designed to work together to produce the aesthetic qualities and durability needed when used properly. These finishing systems have been tested together to verify the ability of all the coatings to work together and meet specific requirements. These finishing systems not only have information about which finishes to use together, but also how to use the finishes.
A finishing system should include how to prepare the wood for finishing. Usually wood is sanded with 120-, 150- or 180-grit sandpaper to provide enough surface area and texture for the stain and coating to get proper adhesion. Sanding with too fine (high) of sandpaper grit can cause poor adhesion because wood coatings adhere by mechanical adhesion. Mechanical adhesion means adhesion by the coating wrapping around the wood fibers. This is in contrast to chemical adhesion which is adhesion by chemical bonding. Metal coatings typically use chemical adhesion as the means to hold onto a substrate. Sanding with too rough (low) of sandpaper grit can leave scratches that are visible after finishing. Besides sanding, other considerations are: moisture content of the wood, temperature of the wood, etc. Consult with the finish supplier for recommendations on the specific stains and coatings.
There are many types of stains such as wiping stains, NGR dye stains, pigmented fillers, toners, etc. Some of these types have many varieties that can vary greatly in the resins, solvents, pigments and additives used to make them. Meaning all wiping stains are not the same, some are not even close to the same chemistry as others. This means that a sealer and topcoat may work great with one wiping stain but not work at all with another wiping stain.
A case in point is using a few different suppliers of wiping stains to go with the high-performance finishes (acid catalyzed) they needed for the durability, look and feel. After finishing with these stains it was noticed that all the panels using stain from one of the suppliers had problems. These problems included adhesion which resulted in the clear finishes chipping and peeling when impacted. The wiping stain from a different supplier, that the finisher had experimented with, did not work with the sealer and topcoat. The finisher recognized this after completing the show panels and the customer’s woodwork. Consult with the finish supplier to determine the proper stains and process to achieve the results needed.
Another consideration is the sealer to use. A lot has been marketed, written and talked about vinyl sealers. Vinyl resins can be used in coatings with excellent results if catalyzed. If they are not catalyzed then you are probably paying more for marketing than results. See my previous blog on Vinyl Sealers. More important than what types of resins are blended to make the sealer is what the finish supplier recommends based on their testing. Many types of resins can provide beautiful and durable sealers and topcoats. Consult with the finish supplier for products that are recommended together.
Another type of finish failure I have seen multiple times is using a very durable topcoat, but skimping on the sealer used under it. Just because the topcoat may be super durable doesn’t mean it can overcome a weaker foundation (sealer) and still hold up. The combination of sealer and topcoat needs to be comparable in quality to work well together. This has led many finish suppliers and finishers to use self-sealing finish systems. This is where the sealer and topcoat are the same product. These finishing systems have been gaining popularity not only because of the results achieved, but also the reduction in number of different finishes to inventory.
Finishing system includes the substrates and continues through each step involved in the manufacturing process. This is a big topic and should be handled in detail with the finish supplier. Using the expertise of the finish supplier will improve the final results you achieve.