Polyurethane Cure Times

      Polyurethane hardening times are temperature-dependent. With multiple coats, the process can get tricky. February 21, 2011

Question
I'm putting down Minwax fast drying poly on an oak dining table, but after four days of drying the finish, it still feels rubbery. I could scratch into it if I tried. How long does it take to harden, or will it always be like this?

Forum Responses
(Finishing Forum)
From contributor R:
Did you also apply this fast drying poly over a Minwax stain? What's the temperature now and what was it when you applied the poly? Is the sample piece you made drier than the table, and did you finish this table the same way you completed your sample?



From the original questioner:
Yes, stain then Minwax polyshades, then fast drying poly. Temperature has been low, around 50 lately. No sample. Will high temperatures make the finish harder?


From contributor R:
From experience, it's very important to allow for correct drying times between each finishing step. If you apply too many oil based coatings on top of each other, and each of those coats has not properly cured, it's very possible that you will end up with a soft coating that may take weeks to dry.

Can you place the table in a dedicated room and crank up the heat? It's too late now, but it's always a grand idea to make a sample before doing the project. If Murphy wants to rear its ugly head, you're not so far into it if the sample goes boink. If the table hasn't fully cured by say Monday, you might have to strip it down and start over.



From the original questioner:
Thanks. I don't mind at all if it takes a month to cure, I just wanted to know if it ever would. I assumed it would be as hard after one day as it would be after a month, but maybe the cold weather isn't helping.


From contributor L:
Polyurethane takes 30 days to fully cure. It needs to be at about 70 degrees to cure properly within those 30 days. 50 degrees is pretty low and will retard curing fully within the 30 days.


From contributor D:
I'm just wondering why you put a fast dry poly over a slow dry poly (Polyshades)? This schedule seems destined for problems. If the Polyshade is not fully cured or at least dry, a fast drying product placed over it will cause problems - cracking of the underlying layers. This is how crackle effects are created. I would do as suggested - put in a heated area and hope for the best.

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