Finishing a table with polyurethane having problems with final coat

[reese_king]

I made an oak and walnut mix table 22" x 40" I stained it then added 4 extra hours to the instructed setup time. I applied 2 coats of 50% thinner and 50% Poly waiting each time for the Poly to dry completely. I then applied 1 coat of 10% thinner and 90% poly. I waited 1 week and then lightly sanded the defects out using 320 grit sandpaper. I wiped down and applied a 30% thinner 70% Poly. All seemed well as I did my final checks for any drips or bubbles. Satisfied I turned out the lights. 5 hours later I went to check on it and see how the Poly was doing. The entire table had turned into alligator skin. It was if I poured paint remover on it. I verified the measurements of each blend at least 3 times. I thought at first maybe I accidentally did 70% thinner 30% Poly but I checked the mix and it appeared thicker than the 50/50. I use mason jars with the measurements on the side so it is easy to measure and I label the mix. I was forced to remove and start over. I have completed my second coat of 50/50. I have done many projects before and never had this issue. The thinner is new and the Poly is less than 6 months old. The wood was never used before and I sanded it for many hours so the wood was perfectly even and flat. I used Elmer's wood glue to join the 22" long pieces side by side.  before I proceed can anyone make a guess or tell me what I did wrong?

[Ox]

That will happen with automotive/tractor enamel paints when you try to clear coat over dry paint.  The clear coat goes right down through all the layers and causes it to wrinkle.  Did you follow the directions closely?  I've learned the hard way to follow what the can says when putting on additional coats.  Sometimes it says to let dry completely, sometimes just tacky, sometimes put on additional coats within a certain amount of time, etc.  Was it very humid while you worked?  Might have something to do with it.  Was it very hot?  Some things need the temps and humidity in a certain range. 

Just trying to give you some ideas...I wish you all the luck.  This kinda stuff can be disheartening.

[reese_king]

yes i followed the directions as I always do. My best guess is it only felt dry. It has rained for a few days before this so I think humidity may have been higher than normal. Humidity in Missouri is always high so that is the only thing I can relate it to. I have came to the conclusion on this project to just do 4-5 coats of the same mix then polish it in a month with Minwax paste to give it a shine. It is drying dull with no shine to it but at least I won't have to do this all over again.

[5quarter]

Your using too much thinner and perhaps not the right kind of thinner. you should be using VM+P Naphtha, not mineral spirits/paint thinner. Mineral spirits is fine for paints but is too hot for poly. You should only thin it if you are using a fine tip HPLV spray gun and no more than 5:1. Also, Poly takes 5-6 days to get to 90% cure. more than 2 coats over a short period of time might cause the film to "shatter", due to the varying states of cure of the various coats. Lacquers, epoxies and 2 part urethanes are more susceptible to this than poly, but it can happen. Also, Poly "can" wrinkle oil based enamels if, A) the paint is not fully cured and/or, B) the poly coat is to thick or too hot. Hope this helps.

[hopm]

I have seen the finish raise with a high moisture content in the wood.

[21incher]

Welcome to the Forestry Forum reese-king. I only add thinner to the first coat when using poly. Humid weather can cause drying isues with certain thinners. I thnk 5 coats of poly can get brittle.

[thecfarm]

resse_king,welcome to the forum.
Been making furniture long?
You will learn,we like pictures.

[Ox]

Did we lose him?  For some reason it bothers me when people ask a question, get their answer and are never heard from again.  I feel like we've been used.  I hope he isn't one of those.

[Dakota]

I feel the same way.