by Rick Hill
Q.
When using a water-based stain (high amount of pigment) with UV cured topcoats, what interactions should one be concerned with? We had a problem with stain adhesion when this combination is used. The stain seemed to pull apart leaving some on the wood and pulling some off. The finishing supplier simply added more resin to the stain and an additive to the topcoat which thinned it out. This obviously costs more. Are there any other options to try, such as higher intensity UV lamps?
A.
As to the pigmented stain, it sounds like your problem is not from incompatibility but from too much pigment. Pigment stains are actually small particles of hard color. They do not soak into the fiber of the wood and do not grip to the wood. Their job is to highlight the grain of the wood while giving a little color tone to the flake. If too much pigment stain is used the color particles just lay on the top of your piece. As you try to put a sealer over the stain, the pigment acts as a barrier to the sealer. The sealer has no fiber to adhere to and then lifts. As it lifts, it pulls the top layer of stain with it. The only way to avoid this is to put down a color coat of dye stain prior to putting on your pigment coat. Dye will soak into the fiber giving you the base tone of color you want. The pigment will give you the grain definition. Many customers do not want to add another step to their finishing process so they try to get the finish technicians to make the pigment stain darker instead of using dye stain. Some finish companies understand this problem and solve it by adding dye into the pigment stain, but there are limitations to how much can be added. Let me know who you are using as a supplier of finish and I might be able to lead you to the right people or group to ask. If you want to send me a sample panel of your finished piece, I can run it through the lab and advise you on color solutions if needed.
Rick Hill is an independent representative and consultant for industrial wood finishes. He has been involved in the woodworking industry for 12 years, and has been known to actually hold, shoot, and clean a spray gun.
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