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I am refinishing a 40 year old cherry table. My wife had bought it several years ago and the finish was not in the best of shape then…numerous areas where the finish had long been gone.
I stripped the finish with a methylene chloride base stripper. I was very meticulous to get all the old finish off of the top. As a matter of fact, I applied the stripper three time to be sure I got all of the old finish and most of the stain off. I did not have any problems with this step. After stripping, I rubbed the entire surface down with mineral spirits and let is set for several days. I then sanded the surface and let sit for another day. I applied a Zar oil based pigment stain and all looked well at this step.
The next day I thinned some polyurethane varnish, approximately in 50:50 with mineral spirits and sprayed a first coat. All went well with the legs, aprons and the leaf. However, shortly after I sprayed the table top, I noticed the varnish rolling off of numerous locations in the top….varnish would not adhere to these areas at all. It is fairly clear that the surface has some contamination, I guess from years of use with the finish in bad shape.
What will act as a contaminate with the polyurethane? I will strip the top and start over, but am not sure what to do differently than last time. I thought the mineral spirits would have gotten any contaminates off. Should I wipe down with laquer thinner instead? Could it be that wiping down several days before applying the stain would have allowed subsurface contamination to come back to the surface and present this problem? Would it be appropriate to stain and then seal with a blonde shellac before topcoating with the varnish to insure no contamination?
Suggestions welcome!
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Brent, I think it could be a combination of a couple of things. Most likely the contaminant is either mineral oil or silicone, two ingredients found in products like lemon oil and Pledge. Both are difficult to remove; mineral oil is barely affected by mineral spirits, and silicone not at all. Use lacquer thinner or a specialty surface prep product available at auto supply houses. The other problem is that polyurethane doesn't stick well to anything except raw wood; even a little oily-ness or contamination is enough to cause cissing.
You could seal with shellac, which is much more tolerant of problems, but the poly won't love the shellac base. A straight alkyd varnish would stick to the shellac better, and I think is prettier, but admittedly not as tough as urethanes.
You could also add fish-eye eliminator (which is silicone itself) to your poly, which would probably work. The only problem is that you won't know 'til you try it, and then you may have another mess.
Oh, the joys of re-finish work!
*My favorite finish for my antiques is a 50/50 mix of marine spar varnish (not poly!) and mineral spirits. I prefer satin. I think it would be hard to have any mineral oil left after what you have done. The shellac would seal and the spar varnish would be accepted, I think. Apply 6-8 coats of the finish. It is impervious to water and alcohol--great table top finish.
*A common solution to this problem, after rinsing well with lacquer thinner, is to put on a thin coat of *dewaxed* shellac. As long as the shellac is dewaxed you should not have any problem with adhesion. I know a couple of high quality pros who do this routinely with stripped pieces.You can buy shellac dewaxed or you can put shellac in a glass jar for a few days so you can see when the wax has settled out. Then use the transparent shellac at the top.Good luck,- Rod Cole
*If I were fed up with dealing with the non-adhering finish and just needed to get the table back in a useable state, here's what I'd do: Strip it off and apply some version of a tung oil finish, something in the Watco typology. The Watco line is available in various tints and levels of glosses. That solution would be quick, easy, pretty much fool proof. If you have the time and patience to keep going for something gorgeous and subtle -- well, that's a whole different issue, outside my limited knowledge and skills. Watco and similar brands make wonderful floor finishes, too.
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