I am/have been refinishing an oak dining table, part plywood, part solid. I sanded to bare wood, lightly stained with a Dalys oil stain and finished with a General Finishes wipe-on gel topcoat. (four or five coats). After a couple weeks the client complained about water stains. I called General Finished and they sent me a different product, their Arm-R-Seal oil and urethane topcoat. I lightly sanded the tabletop as recommended and applied 4-5 coats. Same result, after a week or two water stains reappeared. I tried one more finish, Dalys Profin (oil and urethane I believe) and got the same results.
I now believe that the stains (cloudy areas in the finish in the shape of drops or glass bottoms, slightly lighter than the rest of the finish) are not new but from materials bleeding up from the wood itself. I am reluctant to sand back to bare wood as the veneer is getting thin. I have read that a shellac sealer may be in order. Anyway, help please.
Replies
I'm perplexed at the possible cause, but in any event, if you have a problem originating in the wood itself, you would have to get back to bare wood. Piling on finishes won't help. BUT, you would never want to sand back old finish, you should strip it with a chemical stripper. Then we can try to diagnose the source of the problem, which may be un-even removal of old finish, since sanding won't really do a good job in getting the surface ready for new stain, short of major sanding back to new wood, not ever possible with veneer.
It seem the problem is came from your bare wood.
Before you do apply your finish, make sure it clean.
Wipe of your wood surface with acetone or lacquer thinner to clean it and see how it looks like.
You can do your clear coat with shellac, but if you need the mbetter protection you may consider to use polyurethane clear coating.
Stripping
Thanks for your input. I believe you are correct in needing to strip back to bare wood. It has been recommended to wipe that finish clean with denatured alcohol, acetone or lacquer thinner. What do you think? (I intend to finish with a wipe-on polyurethane )
table top finishing
A wipe on polyurethane is a good choice... BUT do not underestimate the challenge here. Tabletops get tremendous use/abuse! A finish that is reliably water resistant (let alone water proof) is a VERY tall order. I would recommend that you apply about 25 to 30 coats of wipe-on polyurethane. Realize that this is equivalent to only about 6 to 7 coats brushed on. This is minimal protection for a tabletop and yet surely a great deal more protection than your original finish. I very much doubt that your problem stems from within the wood. You might be able to steam the damp areas out with a heat gun but it is a fairly tricky job to do and risks the finish. In any case you'd still need much more protection for that table top.
BTW wipe on gel finishes are quite poor at providing protection against dampness... oil finishes are nearly useless! Polyurethanes are quite good though requiring quite a few coats to get reasonable protective levels (say 6 brush-on coats or 25 wipe-on coats). The gel finishes were invented to create easy faux finish systems for fiberglass doors and do that rather well... they do not provide the levels of protectivity that most tabletops require. I would not use hybrid oil-poly finishes on this type tabletop as the oils tend to thin the coats as well as making them much more permeable to moisture... both BAD things.
Oil based finishes do not become fully water and moisture resistant until they have completely cured. Complete curing can take 3-5 weeks. Prior to full curing, wet and moist thing and hot and cold things should not be placed directly on the finished surface. Use placemats, coasters and trivits. In fact, for good furniture always have some sort of insulating protection.
It's also possible that the discoloring is the result of prior damage to the underlying wood. But, these would show up as soon as the finish became tack-free.
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