Varnish Advice

mikenewman@fron

We have been varnishing over sanding sealer for 35 years marine and poly both. I noticed the label on the BM bucket said do not use under poly. I have had no problem doing this does anyone have an opinion on this. I understand no waterbourne poly over sanding sealer but oil seams compatable.MOPAINT

gideond

A lot of companies say not to use sanding sealer under a poly or varnish. I'm really not sure why. I've never had a problem with it either.

trptman

My understanding is that poly, while a tough durable finish, does not adhere well to other finishes (in theory anyway). It relies on a mechanical bond, which is why you sand before each coat, to create small scratches for the new coat to fill and "cling to". Or something like that. Sanding sealer probably sands out so smooth that maybe the poly wont cling quite as well. I'm doing this all from memory and its been a while since I looked any of this up or talked to anyone about it. I could be wrong-some of the details are a bit fuzzy. I try to avoid poly when I can. it is harder to get a smooth finish on I find. It is a tough finish which makes it tougher to sand to get smooth etc.
Just more work unless you really need its toughness.
In practice, I'm with you-never had any problems with anything over sanding sealer. I'm sure in the lab, they figured out it doesn't quite hold up as well while doing trials with it.

mikenewman@fron

What caused the subject to come up my cabinet maker freind saw it on a bucket of BM sanding sealer and even called the company. I just looked on the label of my Cabots sanding sealer and it says recoat with conventional or oil based poly. I still say it is no problem. I think BM is just over cautious. MOPAINT

gideond

I could be a matter of formulation as well. Davis Paint recommends their poly to go over their sanding sealer, especially for floors.