I am trying to prime new double humg window sashes I built from Poplar. I am using an oil based primer from Sherman Williams but it is not setting up as I expect it to. The can says no thinning is needed so I first tried priming with it without thinning. it went on prettyh thick and after 5 days still was soft. I could peel it off with my thumb nail. So I removed it all (a big job) and decided to try thinning the primer 3 parts primer and one part laquer thinner. This time I tried it on a new piece of pine I had on hand so I would not have to sand if things did not work out. Primer still seemed thicker than I expected. After 24 hrs. the primer is not hard. I tried lightly sanding but primer would easily come completely off the wood. DThe wood does not seem to be soaking it up at all.

What am I doing wrong? The temp is between 60 and 75 degrees in my shop and humidity is moderate only.

Any help is much appreciated.