Air bubbles in finish
Looking for help diagnosing the cause of some air bubbles that are appearing in a lacquer finish.
-This only ever occurs on veneered plywood. White oak, walnut, alder, maple etc.
-One side of the panel will have no bubbles, the other side will. Size, location and frequency vary. Sometimes only one, sometimes 20+.
-They can occur over a stain or just as a clear coat.
-Spray pattern is consistent
-They only ever occur on the first coat
-It’s not consistent. I can go whole projects without having an issue only
for it to pop back up later.
Pictures are a stained Walnut panel.
Any thoughts are appreciated, I’ll answer any questions as timely as I can!
Normally I would blame such problems on the gun not atomizing properly, but you say it only happens on plywood and then only on the initial coat. This leads me to think that there is some type of off-gassing going on with the plywood probably adhesive related. You don't mention what type of lacquer you are using, but lacquer solvents can be very reactive and it's possible it may be having some effect on the plywood adhesive in places where the veneer is thin or the wood a bit more porous.
Have you tried an initial sealer coat? Maybe shellac? A retarder added to your initial coat might buy enough time for the gas bubbles to dissipate as well, just be careful of drips and runs.
Thanks so much.
We’re using a pre-catalyzed product, (Coverdale is the manufacturer).
We typically don’t use a sealer, but I’ll give that a try.
You should be able to test my theory. Take a scrap of plywood maybe 2' x 2' and sand it heavily to the point of almost sanding through the veneer and then do one side with the sealer one without to see if it has an impact.
If you do decide to use a sealer like shellac and since you sound like a pro I would suggest you remake your sample boards you show to customers because shellac will likely change the tone of the finish adding some warmth.
What are your thoughts on using a propane torch to quickly skim the finish after applied to relieve or pop the trapped air pockets.
This is a fundamental step when using epoxy -to relieve trapped air.
Reference Stone Coat and Counter Top Epoxy for better clarification.
Obviously air is being trapped and needs to be relieved.
When working with epoxy on a router edge it is very important to work the edge and elevate the trapped air
If he didn't turn into the human torch from an open flame around lacquer fumes, unlike epoxy which can be softened by heat lacquer would just dry quicker.
Indeed. "Give a man a fire and you keep him warm for a day; set a man on fire and you keep him warm for the rest of his life." Terry Pratchett.
Open flame and lacquer DO NOT MIX.