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I made the grand daughter a play table last year. The top is laminate with a 2" oak a boarder around it, finished with lacquer. The finish on the oak now looks as old as she is (6). I was wonder if I could put poly over the lacqure . What would be best if not the poly?
Thanks
Harold,
You don't want to put poly over lacquer or lacquer over poly. The two are not compatible with each other as you will have adhesion problems if you try it. If you're keeping the lacquer I'm not sure I would do anything other than perhaps a wax/buffing. If you are stating from scratch then there a lot of possibilities with many different types of finishes.
The best way to repair the lacquer finish is with more lacquer. You "can" put polyurethane over lacquer after light sanding, but there is no point in doing so. It's not going to be any more "durable" than the lacquer.
What Jim said. Give it a light to medium sanding, depending on the damage and shoot another coat or two.
If you really want Poly it will go on OK as long as the old finish is fully cured or you use a barrier of sealcoat (dewaxed shellac). I wouldn't go to a poly finish just because several others are durable and are repairable. Polyurethane isn't really a repairable finish.
Joe
Poly will go over it fine. Just use some 220 to rough it up. I would go with a few coats of wipe on. It will give you a poly finish but not that plastic look.
Non catylzed lacquer doesn't take abuse very well. For kid projects poly seems to hold up better.
Yes, you can put poly over lacquer. You could also put mayo over it but that doesn't mean you should. I stand by my comment. Both Minwax and Sherwin Williams recommend that you DON'T do that. I'm not sure why you would want to put it over lacquer but if I had to commit to a finishing schedule for a lot of material I would not take an approach that, yes, can be done, but because a lot of reputable vendors, authors, etc. recommend that you don't do that. You may not have problems as described with the sanding but I would not be willing to take that chance on a large project.
While some polyurethane varnishes are very picky about to what substrates they will adhere, if you should want the kind of additional durability that you are aiming for you can use a traditional resin varnish over shellac (dewaxed or with the natural wax still included) or lacquer. It is necessary that the surface be abraded--220 or 320 grit will work fine--so that the varnish has some "tooth" to grab.
I did a little bit of research to make sure there was some substance to what I was saying and a couple of things keep coming up and that is that the variations between the chemical compositions of the poly vs. lacquer may be fine and some may not be as far as compatibility. Even with the sanding approach, I found several posters on sites like woodweb, etc., that had problems. Obviously it works fine but the variances is what I would worry about. Basically a lot of what I've read from people like Flexner, etc. is that manufacturers tend to not describe their products truthfully and in ways that make you think it is something other than what it really is. I guess that's what would concern me on following an approach that there is such a disagreement on, but then I've never personnally tried it. May be the best thing for me but I've just never tried it.
Generally the incompatibilty works in one direction here. Lacquer over varnish doesn'[t work well because the strong solvents in the lacquer can attack the varnish film. Fully cured --several months or a year-- varnish is better able to withstand this onslaught than recently applied varnish. But nitrocellulose lacquer dries very quickly, without a lot of curing time needed because it is basically an evaporative finish. The solvents in most varnishes are much milder, typically just mineral spirits, and are unlikely to attack a dried lacquer film.