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Waterborne Lacquer Adhesion Mystery
Question
I'm really at a loss as to what to do now. I have four chairs that I'm afraid to put the finish coats of Kem Aqua Lacquer on in fear that this problem won't get any better. Any suggestions as to what happened and what the solution to this problem may be? Forum Responses
From the original questioner: These were new chairs and had never had any sort of finish on them before I started. From contributor D: The SW BAC stain may have some type of oil in the formula for wipeablity. That may be the cause of the poor adhesion. Does SW recommend BAC stain under water clear coats? From contributor Y: New or not it sounds like there is contamination of some type be it wax/oil or other. If it were me I would strip them and wash with solvents (lacquer thinner/alcohol/acetone/toluene/etc), re-apply stain, give them a thin coat of 1- 1 1/2 lb. cut dewaxed shellac freshly solved, grey scotch brite them and then apply the kem aqua. Do samples first and keep note of where and which had the worst problems. You can also just solvent wash one of the areas that's bad and spray again to see if it clears up the problem. From contributor W: I've seen this before with BAC and other solvent-based stains. There is a percentage of mineral spirits in the BAC that is probably causing the adhesion problem. Before applying the WB topcoat wipe the dried stain with a 50:50 solution of water and denatured alcohol. This will remove the surfacing mineral spirits and other oils that may be popping up. You might get a bit of color bleed if the stain has dyes in it, but it will be minor. Next, a tie coat of dewaxed shellac will act as a barrier coat between the BAC and the WB. From contributor J: What temp is the shop? I'm wondering whether 24 hours is enough time if it's cold. From contributor R: If the shop wasn't 70 plus degrees, your stain wasn't dry enough to topcoat with WB - especially with oak. It's famous for stain getting down in the pours then wicking back up after you've wiped off the excess. With solvent stain and WB sealer on oak, I would've wiped two or three times with an hour between wiping. I think you'll have to strip and start over. From contributor B: SW probably over tinted the BAC. How many ounces of colorant did they add to the gallon? From the original questioner: The normal temperature in the shop is 65-67°. The stain was heavily tinted and had around 10oz. of colorant added to the gallon and I suspect this may be the root of the problem. I hate the thought of stripping these chairs but if that's what I have to do I'll do it to make them right. Thanks to all of you that helped me out here, I really do appreciate it. From contributor W: Have you checked the adhesion since you first posted this thread? WB's have a tendency to gain adhesion over solvent stain as the solvent off-gas and the WB's continue to cure. I have seen massive improvement of adhesion after 200 hours. From the original questioner: Funny you should mention that, it does seem to be getting better over time. Hopefully everything will be ok and I won't have to strip these chairs. I'll let them sit for a while and test them again. From contributor Y: 10 % of colorant in 118 oz (1 gal. total) of vehicle is not over pigmenting. As long as all the excess is wiped off! It's when people leave excess on that problems can develop.
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