Shellac Before Poly Finish on a Custom Table
Shellac is a good sealer coat to apply to a furniture piece while still under construction, during a delay before final finishing with poly.October 19, 2014
Question (WOODWEB Member) :
I've just glued up a walnut table top, 1 1/8" thick and 55" diameter. I'll attach battens with slotted screw holes today. I will lay handmade ceramic tiles in a 15x15 cutout in the center. The potter is behind schedule and the tiles won't be ready for two weeks. I'd like to seal the top with shellac now and finish it later (five coats of wipe on poly) over the shellac. I still need to work the top (sanding, and cutting the hole for the tiles, attaching substrate for the tiles, cutting small chamfer on the edges). I figure I can do these things after sealing it with a coat of shellac. Is this true?
From Contributor B:
Yes that's true. There are some people who have had a problem with the wax that's in most shellac, so for that reason you should use SealCoat - it's de-waxed shellac.
From contributor P:
What's your hurry to seal it if you're going to expose the raw wood through additional working?
From the original questioner
Thanks for the tip on unwaxed shellac. The reason I want to seal the top now is that the remaining work I have to do on it will take place mainly after a period of about two weeks. I can't make the cutout for the tiles until I have a final size, and they won't be fired for a week or two. When I have that size, I can make the cutout and do that work (involves cutting the hole, cutting a rabbet from below, attaching substrate, and so on). Then I finish the top with poly (it has to have finish on it before the tiles are installed). I want the top to be sealed for that week or two while I wait for the tiles. After I make the cutout, finishing with poly takes as long as it takes (three or four days) and things go pretty quickly after that. If I have to expose raw wood during that long interval, I'll hit it again with shellac.
From Contributor B
Sealing with the shellac will make it easier to prep surface for finish coats. Sealing will prevent any grout, mortar or water from staining the bare wood. Shellac is also relatively easy to sand off if you want to stain or finish the bare, sanded wood.
From Contributor R
I have always held firm in that you never use shellac under poly. However after reading a discussion on this issue I have changed my mind after testing it out. I normally use a 1 to11/2lb. cut for sealing and I went to a 2lb cut for testing purposes and to date there are no problems on my test panels (birch, maple, pine). I use shellac on everything.