Poly problem

[Ron Citerone]

I just applied Helmsman exterior OIL BASE gloss poly to the top of a 2'X6' work bench top.

I have used this same can of finish full strength on the legs and cross stiles, 3 coats, last 3 days no problems other than some dripping.

Today I raised the grain on the top with a damp (not soaking wet) rag with water on it and did the final sanding.

3 hours later I applied the poly.

I thinned the poly with some paint thinner and it flowed on way better than full strength.

10 minutes after application I started seeing a kind of bubbling on the surface forming as I watched (NOT AIR BUBBLES)

I tried to smooth it with the brush and it actually continued and got a little worse.

After 20 minutes I started wiping it with an old t-shirt and think I got it looking ok, but it took much wiping.

I dumped the thinned poly back into the half can of finish.

1) What the heck is going on here?

2) Do I dare use the finish for a second coat tomorrow or get a fresh can and use it unthinned?

The only thing I did different on the top compared to the legs was raise the grain and thin the poly with paint thinner.

I am pretty experienced and never had this problem before.

Thanks, ron

[Prashun Patel]

A bubbling finish can mean that you thinned with an incompatible solvent. What kind of paint thinner did you use?

[Ron Citerone]

A bubbling finish can mean that you thinned with an incompatible solvent. What kind of paint thinner did you use?

Klean Strip paint thinner. Says thins oil based paint stains and varnishes. Made with mineral spirits.

[Wayne Lomman]

It is almost certainly an incompatible thinner. Use the solvent recommended by the manufacturer of your coating material. There are plenty of solvents that are OK to wash up afterwards but only ever use the correct stuff as a thinner. Cheers

[Ron Citerone]

It is almost certainly an incompatible thinner. Use the solvent recommended by the manufacturer of your coating material. There are plenty of solvents that are OK to wash up afterwards but only ever use the correct stuff as a thinner. Cheers

Where do I go from here? OK to apply unthinned finish on top of this after it dries?

[Bennett Ostroff]

I'm confused about why you raised the grain before using oil based poly. That's really only needed with water based products. My guess is the wood didn't completely dry and there's some interaction with the moisture and poly/solvent.

At this point I would probably sand back down to bare wood and give it 12-24 hours to make sure its good and dry. Maybe put a fan on it. Then start over with the poly, thinned or full strength.

[Rich Engelhardt]

Never mind....
The old Helmsman wasn't a poly and wasn't recommended for interior.

I see by the title you used the newer poly stuff.

[Ron Citerone]

Okay, here is what I think. After sanding to bare wood and allowing to dry all day I tried again with a fresh can of unthinned poly. I tried the old thinned finish on a seperate board from a different source and it was fine, so the problem is with the wood I used for the top. When I originally raised the grain with a damp rag, it was barely wet and I really don't think that caused it (I've done this many times before). I suspect the poplar that I just purchased may not have been quite dry enough. Gonna let it sit in my basement with a dehumidifier for a while to dry more. Woodworking is a humbling hobby!