I am finishing A-1 walnut veneer on 3/4″ plywood. I am using a Natural Gel Stain to bring out the grain. This looks great after application with no problems. However, when I apply the first coat of clearcoat small random spots (up to 1/2″) appear which look like something has been splattered in the surface. They do not appear after staining, only after the clear coat is applied. Further coats of clear coat do not fix the problem. The spots have the colour of unfinished walnut (dusty brown) and feel slightly sticky.
I am using a Gel Stain (Varathane #403 Natural) which is wiped on, and a water based clear cloat (Varathane Diamond water based) applied with a brush.
I can re-sand the clearcoat and re-apply the stain which makes the spots disappear, but they re-appear after the clearcoat is applied.
I have used this same process, stain and clearcoat on solid pieces of walnut and do not have this problem.
Suggestions?
Replies
Seems like an incompatibility between the "stain" and the top coat. Why this should be different over veneer vs. solid wood isn't clear, though veneer often takes finish differently. Did you thoroughly wipe off excess "gel" after you applied it? Did you give it ample time (and warmth) for it to fully cure before you applied the waterborne finish?
I put "stain" in quotes since it should be clear, that except to marketing folks, "natural" stain makes no sense. Stain is stain because of the pigment, not because of the binder material. A coat of any oil based finish would have given a similar coloration effect. Even better in your situation, a coat of dewaxed shellac would have provided the impact, but would likely give a much better foundation for the the waterborne finish to adhere.
If you have been working on the project itself, not just scrap, I would recommend using a chemical stripper to go back to bare wood. Then you can apply dewaxed shellac to bring out the wood color and grain and then the top coat. Sanding isn't recommended. First, it doesn't get finish out of the pores evenly, and probably most importantly with plywood, there just isn't enough thickness in the veneer to allow more than a VERY light sanding with fine grit paper without risking cutting through the veneer. That's a problem you do not want to fix.
Might be the plywood....
Big,
The problem could possibly be in the plywood. When I run into problems like this it is usually caused by uneven glue under the veneer or bad spots/voids in the core of the plywood that you can't see. A-1 ply is good stuff but there is still a possibility that it came from overseas and that quality control is nill.
Good luck,
Lee
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