Reply by Fred Hargis

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Posted on Poly over Zinsser amber Shellac?

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Fred Hargis

4956 posts in 2463 days

#1 posted 06-26-2012 01:55 PM

Danr, in most circles “poly” is varnish, it’s made from polyurethane resins (there are other finishes referred to as “poly” from time to time, mostly water born). The difference between the “poly” and non-poly is the base resins used, and sometimes the oil they are cooked in. The P&L and cabot are alkyd resin/soya oil formulas, the S&W is an alkyd resin/linseed oil formula. There is also Waterlox Original, a phelonic resin formula (not sure which oil they use). Linseed oil formulas are normally what the pol varnishes use, and that is why they have that decidedly amber cast to them. SW fast dry is that way. But open a can of P&L (soya oil) and it looks a purplish-gray in the can, the Cabot is a goldish (I guess) hue. So if you have used what most folks call “poly”, you have indeed used varnish. Also, putting seal coat on top of the amber might still have a risk. Shellac tends to melt into itself (the alcohol in the new coat dissolves whats already there) so so of the wax can come to the surface. I won’t claim the non-poly varnishes are better than poly…it’s chief attribute if scratch resistance. But the other varnishes are just as good (my opinion) as poly on any furniture projects. Poly is great for floor finishes. For water and stains I also think the non-poly is just as good, and may be better than poly. I’m sure sure what exactly you are putting the varnish on, but unless it’s the floor I think the others will be just as good. BTW, it’s actually the urethane resins that cause an adhesion problem with the waxy shellac, that’s why the others will still work.

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