i stained and used 2 coats of water bourne polyurothane on a large piece of 3/4″ mahogany plywood that is part of wall paneling. now i noticed a appr. 8″ diameter bubble in the mahogany veneer. the veneer somehow seperated from the next layer. how do i fix that without destroying the finish. the plywood is actually called sapele which i think belongs to the mahogany family. the 3/4″ plywood seems very light in weight. does that mean its a cheaper grade? thanks for any help.
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Two possible causes of the bubble are:
Either problem can cause a bubble and the first one is fairly easy to fix.
If you're dealing with a simple veneer separation, get a syringe with a fairly large bore needle and inject glue in 3-4 places around the bubble. Use some plastic to cover the bubble and put some pressure on it to force it down. Let it sit for a few hours and remove the plastic, clean up any glue squeezeout, and touch up your finish.
Sometimes, however, the bubble won't lay back down correctly and you'll probably have to replace the bad piece.
I believe you may have Meranti, but that is not the problem.
WB finish is notorious for grain raising and in your case expanding the top veneer to saturated expansion.
Hate to say it, but yer hosed. Birch Ply will do the same, the face veneers are way thin and the expansion causes the internal voids to telegraph/bubble.
The old inject glue with a hypodemic nerdle and weight MAY work, but I have seen more failures than sucesses.
In the future, spray a light coat of WB..and another..then a full wet coat after the base is sealed. If you are brushing or rolling..you still need to seal the grain..and spraying is the cure.
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Not being able to see the case in point, is pretty difficult to give a proper assessment. i personally would let go , of trying to save the finish. When something is "snake bit" like that , All fancy foot work you do may open your self up to more obstacles. 8" inches bubble is a major product flaw. My initial instinct would be replace it , or cut it out fill and find a corresponding veneer to cover and refinish. But again no picture , i'd being a used car with a sheet over it . I would look into the product flaw end of this and perhaps a compensatory thing could happen for you . Regardless best wishes and i personally would like to know the outcome .
If the veneer is separated from the substrate(not a void), try ironing it with a diaper or towel underneath. Often a combination of heat and pressure will redress this problem. Some finish touch up repair is likely.
Expert since 10 am.