What should I do about partially tacky urethane finish?

Question

so I've been refinishing an interior bench. The bench had a very old polyurethane/resin finish which I sanded completely off, there was nothing other than bare wood when I stained it. I stained the wood with a maroonish oil-based stain and let dry for 24 hours. I used a tack cloth to remove any residue that might have fallen on it and it felt good and clean, ready for the urethane finish.

I mixed 50/50 urethane with the safer mineral spirits they have out now (the more environmentally friendly stuff) for the first coat and I brush applied it lightly last night. I wanted to do a light sanding and apply another coat of 100% urethane this morning but parts of the finish from last night were still tacky while the majority of the bench was perfectly hard like I expected it to be.

Granted it's cooler (winter time) now but it's inside the house and parts of the finish dried just fine. Should I give it more time or should I use the mineral spirits to remove the tacky finish and reapply? Could the tack cloth have left some of its waxy residue on the wood which would cause the finish not to soak into the wood? I didn't rub the tack cloth into the wood by any means, just a light touch to pick up the crap.

Answer 1

It's possible it's just the cool temperature and it will dry in a few days. It won't hurt to let it sit several more days and see if the tacky areas harden up on their own.

However my suspicion would be a compatibility problem between the urethane finish and the "green" mineral spirits. Although they probably say then can be substituted for real mineral spirits, I've heard of mixed results when using them for thinning oil based finishes. For a future project you could select all water-based finishing products which would have lower VOCs and would not require thinning with any solvents. Or use standard mineral spirits for thinning and save the "green" ones for cleanup.

If the finish doesn't harden on its own I would try to remove most of the finish from the tacky areas as you described. I would do it in stages with some drying time inbetween because if you remove too much you will likely also remove some of the stain resulting in inconsistent shading. In that case you may need to strip and refinish a larger area (or live with the spots).