Polyurethane won't cure

Ugh, I've had that happen with higher temps even. I refuse to use Minwax. I dont know why it does that. Best I can say is bring it in the house near a heater vent. The body I did never did get real hard though. You may want to just strip it. If you want to do a quick and dirty finish like that I hand brushed this stuff and it cures fast and levels out great.

 

What type of Minwax poly did you use and what did you thin it with?

 

Welcome to TDPRI, by the way!

The minwax poly finish I did last summer took quite a long time to cure. It was a couple of weeks before I felt that I could handle it casually without easily dinging it up--but note, this is a paulownia body and just a "learning" project anyway so I was not that concerned about it. If it has spent that month at 35-50 deg then give it at least a few months in the warm before giving it up.

Good luck!

 

Ooops ouch I meant to type "at least a few weeks ..." I think if after several months at normal temperature it weren't pretty hard I'd be pretty disappointed.

 

Your problem may be in the paint thinner, while you can clean up with thinner I rather doubt that it suggest that you thin the product with a standard thinner or if you should thin at all. Modern oil finishes are really modified oils, depending on the container size you purchased, gallons have a different formula than quarts. It may be the poly finish is delaying the evaporating of the thinner you used. I would double check on the label to see if they recommend thinning but I do think your finish will harden eventually

 

Uncured poly is sticky.

I think your issue is that it's thinned and wiped on--which makes the cured finish really thin. It's as hard as it will get, but the wood beneath it is really soft and provides no support.

Cured poly is not hard like glass. It's only as stiff as whatever you apply it to. Coat a piece of printer paper with it and you can still roll up the paper after it's cured.

 

yeah... I doubt it will ever cure completely. I've used the Minwax wipe on quite a bit in the last 2 years (complete set of kitchen cabinets, 7' island counter, 2 guitars). wipe it on generously at full strength with the minimum motion. don't hit it more than 2 or 3 times, then leave it alone. all this work done in my garage in AK in the winter (mostly) temps there in the low 50s. for an applicator I used a replacement element for applying floor sealer. I got it at Lowe's, about 8x12 inches(?) maybe BlueHawk brand. one fuzzy side, one foam. the fuzzy side worked best. cut off a square, use it, stuff it into a baggie. good for a couple days then it gets too stiff

 

What kind of wood? What kind of filler? What kind of primer? How did you apply the poly? How much did you thin it? How long between coats? Does it still smell quite a bit, indicating it is still drying? Did you use it on a maple neck? Is that any harder?

I used the identical poly on a maple neck, and it was very hard within 3 days. I gave it a week just in case. No primer. I did not thin it and used thin coats. As I recall, 4 coats - dried 1 day between coats. Applied and dried at room temperature.

There are many variables that effect finishes. The more information you can provide helps narrow down the reason for the problem and possible remedy.

Many factory finishes today use catalyzed, 2-part poly which makes it similar to epoxy. You aren't likely to get the same hardness with typical consumer-grade finishes.

 

Assuming you brought it indoors to dry. a week is plenty of drying time. What was the polyurethane wiped over?

I would remove the finish and try again with a different topcoat.

 

yeah... sounds like it's "Pauloweenie" wood... about 1/2 step from balsa. nice & light, but self-relicing. touch it and theres a dent. thats a different problem, and not related to the finish. get rid or the gooey top coat and put on something else

 

Finishes pretty much always have an acceptable temperature range right on the container. Cold temps will absolutely affect curing. And remember, it's not just the air temps that have to be within the range; so does the workpiece and the finish. Get the project into a "room temperature" location to see if it will fully cure. Oil based finishes can take a long time for that even under ideal situations...

 

Do you have a maple neck? Does that finish seem harder? Will it dent with a fingernail? If it does, then the finish may be part of the problem. But if it acts a lot different, it is primarily the soft body wood.

 

weird I too think the problem may lie in the thinner used. did you put on lots of coats? In my experience poly gets pretty hard in a couple of days. rags left to dry get pretty stiff too