quick polyurethane finish questions
I'm applying polyurethane finish to the stained crib I built.
I just applied layer 1 today. despite careful efforts, bubbles survived and dried in the finish.
Getting ready for second coat.
Anyway, just some quick questions.
I'm using Minwax fast drying polyurethane. The can says to sand with 220 between coats. I've heard other people say they use a finer grit.
Also, I plan on doing 3 coats. After the last coat, if there are bubbles or other imperfections, should I do a final sanding after the last coat?
Lastly, I have to transport the crib from the shop to the house. it's a drive of several hours. If I'm on schedule, the final coat will be applied about 36 hours before I plan to move it. Will it be okay to stack the finished pieces in my SUV and drive them, or will the finish be too soft? And will it still be giving off fumes?
220 is recommended between because it will not wear away at the previous layer unless used aggressively. You can go finer, but I find anything higher than maybe 320 will not level the surface properly. The 1st coat will always have bubbles. Especially in oil based finishes. Air is traveling through the pores of the wood and get trapped in the finish as it dries. Oil takes a long time to dry, so you will get those air bubbles. You will get less with additional coats. I would be careful stacking those parts on top of each other. They will stick together. The poly will appear dry in 24 hrs but doesn't cure until about 3 weeks. As for the last coat, don't sand. I usually wax it with 0000 steel wool and buff with cloth. Hopefully the smell of the poly wont last too long. I recently made a dresser for my son and used a the same poly and it smelled for 2 months. It was a gloss poly. I find the gloss smells much more than semi or satin. Good luck.
You can thin the poly for the last couple coats and make it more of a 'wipe on' poly- works great and no (less?) bubbles and a flat finish.
The last piece I did, I sanded between poly coats and thinned the poly more and more each coat.
When you put a thick coat on you can use a bristle brush and 'tip' the bubbles to pop them- be gentle. I found the slower and steadier I was applying the poly the less bubbles appeared. I used old cotton undershirts that had been washed probably 200 times to apply the poly, cut and folded over a few times to make an applicator pad essentially.
The final couple of coats were fine grit, gentle hand sanding and really thin (thinned out) coats of poly- turned out like glass. I used oil based gloss poly.
Does take a while to dry but the thinned poly seemed to dry much faster than full strength so maybe you'll be OK. I wonder if wax paper between the pieces would help?
Watch out on that top rail of the crib, infants like to gnaw on it and I'm sure poly isn't healthy- maybe a top rail plastic protector is in order, and it'll protect the wood and finish.
My staining protocol is using cheesecloth to apply the stain and a foam brush for the poly. No streaks, bubbles or brush hairs. I use steel wool, 000 or 0000, between all coats, and wipe down with a tack cloth as needed.
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