Polyurethane on BLO?

[Pete Costa]

Hi all. I’m helping a friend with a midsize beechwood table. Can we put polyurethane over an existing BLO finish? If not, are there other options more resilient than just more BLO? What steps can we take to ensure the best adhesion? Many thanks, Pete

[Christopher Herzog]

I have done it before with mixed results. First try, guessing that the BLO was not totally dry. It bubbled up underneath and had to be sanded off. What a treat that was. Second time I tried the BLO was fine underneath and it came out fine.

My two cents....

[Jim Becker]

BLO by itself is completely compatible with an oil based varnish or "poly" if it's cured. Many even use BLO as a base ingredient before they are "cooked". If it's a BLO and wax finish, however, the issue is the wax. The finish will have to be completely removed and any residual wax done away with chemically. Alternatively, a barrier coat of wax free shellac might provide the adhesion you need. "Poly" doesn't even like to stick to itself which is why abrasion is required between coats that cure for more than a certain amount of time.

[Pete Costa]

Thanks gents. Gave it a few days and did a test inside an apron. Everything looks good. Appreciate the support. Pete