A shout out to all of the finishing experts, professional and amateur alike. I've been working (for too long now) on completing a sign project done in western cedar and have been having a tough time with the finishing. The planned schedule was relatively simple--an epoxy sealer (Total Boat) followed by several coats of a clear gloss spar varnish (Epifanes) followed by a matte finish spar varnish (also Epifanes)
After sanding down to 220 grit, the bare wood had been prepped with a light wipedown of acetone, to remove any residual surface oils. Then, two separate coats of Total Boat Epoxy Sealer were applied following the directions--the second coat going on just after the first had reached a tacky state.
The epoxy sealer coats were applied in my garage shop, which I heat for short periods with a Fahrenheat 5000, and the interior temp is usually around 55-60 degrees F. But here in the Pacific Northwest the humidity levels can typically be around 50-60% this time of the year. So the second sealing coat took a little over a week to fully cure.
Following a light sanding with 150 grit, I laid down a first coat of Epifanes Clear Gloss Spar Varnish and allowed that to cure for a period of about three days (again, the temp and humidity levels affected the length of the cure time). Then upon application of the second coat (after a light sanding with 320), I ended up with a severe cracking effect. I attributed this to an incomplete cure of the first coat, so I allowed the cracked coat to cure for almost two weeks and the sanded it off using 150 grit. After vacuuming off the surface and then wiping down with a dry cotton rag, I brought the whole project into my house and allowed it to stabilize for a little over 12 hours. Then, I laid on the first new coat of varnish, thinned about 25% with mineral spirits.
The current result was a cracking effect even more pronounced than the first (pictured below). Any ideas what's going on here? I should point out that this did not happen on the back side of the project where I followed the basic schedule described above entirely in my garage shop, and the finish turned out nearly flawless. So why the cracking on the opposite side, could there be some kind of reaction taking place with the epoxy? Or, is it possible that sanding down to remove the initial varnish coats wasn't thorough enough, and I managed to leave enough behind that it reacted (again) with the fresh coat of varnish?
Short of completely sanding down to bear wood I'm out of ideas for how to correct this issue or even why it's happening. Any suggestions would be appreciated.
VarnishCracking2.jpg