Built a dining table, sinker cypress. Finished with oil-based polyurethane because it's very humid here and I haven't decided if I'm going to epoxy pour the top later since cypress is so soft.

Anyway, did the first coat of oil poly exactly like I've done 100 other oil poly projects before. Went out the next day and it was like touching glue. Waited another 24 hours, still tacky. Put a fan on it. A week later it finally feels cured

Started sanding it today (220 grit, random orbit for more info) and the sandpaper started gumming up with half-cured poly. I went through 10+ sheets of sandpaper on the 9 ft table.

What is going on? I applied what I thought was a very thin coat. It's been about 11 days now, so even a high humidity cure should be complete

Wood not dry enough?

I got tired of messing with sanding brushed layers that were thick and hadn't fully cured and switched to wiping oil-poly a few years ago and have had great results. For one, I thin with mineral spirits, which helps make the layers thinner and eliminates bubbles. The layers usually dry out faster. That first layer soaks much easier into the wood grain, too. I also have been able to manage more complex shapes, vertical surfaces, corners, etc. much easier. Overall has just become much more predictable for me.

I typically do 5 layers. 2 layers at 2:1 mix (poly:mineral spirits). Then a light sanding or scotchbrite. 2 more layers at 3:1. Light sanding or scotchbrite. Final layer at 6:1 mix. I definitely wear a respirator when I do it. Sounds like more work, but it really hasn't been for me. I've done more layers on a kitchen table-top to beef it up for the wear & tear.

Hardwood place said it was kiln dried, but I guess I don't know. I can borrow a moisture meter thing from a carpenter friend and check the underside

Ben - you're saying you're still applying a thinned poly, just using a rag to wipe it on instead of a brush? I can definitely see how that would be easier to control the thickness if that's what you're saying

What brand of poly did you use? Have you done any other work with that can of poly? Or is it fresh? How long have you had that can?

I agree with what you said, even in humid environments, poly should dry. In my experience, the only problem that may develop in humid environments is blushing; a white haze that develops as moisture is trapped underneath the top surface of the drying poly.

But non-drying poly, never heard of that? My first guess is bad poly, drying agents not added, or turned to solids and not incorporated by stirring, or became inert due to age?

I have had real good luck wiping on thinned General Finishes poly. There is a difference in quality. I start with a couple coats of thinned shellac.

Tango.Mike said:

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Ben - you're saying you're still applying a thinned poly, just using a rag to wipe it on instead of a brush? I can definitely see how that would be easier to control the thickness if that's what you're saying

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Honestly, I think thinning has done more for me than wiping. But the rags definitely make it easier to wipe away excess than a brush. Make sure you're using a lint-free cloth if you ever go that route. I used to use cut up old t-shirts (theoretically lint-free), but switched to wiping clothes and they just did a better job.

IMO, Cypress really needs to be sealed first before applying an oil based finish. Cypress contains a natural resin that can interfere with adhesion, especially oil-based polys. The resin can also be released during sanding, potentially contaminating sandpaper, ultimately leading to inconsistencies in the final finish. I know dewaxed shellac is a popular choice of sealer for Cypress...not sure what the best option is. I'm guessing that any water based sealer would work, but I have no experience with such.

Excellent feedback all around, thanks boys

Was using Varathane Ultimate Polyurethane, researched batch code and it might have been made around 2020. I got it from HD. I normally get finishes from Rockler or the local hardwoods place, but I was trying to get it complete for a grad party and went with convenience

Good info on the cypress bonding, this is my first time working with cypress. I definitely didn't thin it enough, I thinned it at like 10:1.