I've never heard of that happening with varnish. 

You are using a one part varnish, correct?  How long have you waited for the Varnish to dry?  It takes about 12-16 hours to be tack free.  Im guessing you have waited overnight and still tacky?

Without knowing the enviromental conditions did you thin the first coat of varnish? If you rolled on a coat it could be too thick and trap solvents. If that is the case it could take days to dry.

It's a one part varnish. I added about 10-15% brushing thinner (as recommended). I thought this may be a cause the last time this happened and changed solvents but it didn't make a difference. Usually when varnishing over wood, I'll cut the varnish 50% on the first coat for penetration, then 30%, then 20%, then 10% for subsequent coats. With epoxy, there should be no cutting in of varnish since it should not be penetrating and the only reason to thin would be for ease of application. 

It's been a bit humid here in Va Bch and not much airflow in my garage but the epoxy didn't seem to mind. It's going on 72 hrs. I guess I won't be launching this weekend...

You may want to call West Systems. Even if the epoxy is hard it may not be fully cured.

Did you use Epifanes brushing thinner? Or another brand?

I thought of that too but I've kept to the same company brands. I've also done different ones before and I seldom saw a differnce.

I've wondered if air circulation would help but I think it would end up putting a lot of dust on the varnish.

It's probably not the thinner, then. I'd expect that using thinner would make the varnish dry faster, since the coats are thinner. 

If you really want to get to the bottom of this, you can use the process of elimination:

- To rule out the varnish: Put some varnish on a piece of raw wood and see if it cures more quickly.

- To rule out the epoxy: Put some varnish over a different brand of epoxy, like MAS with slow hardener.

- To rule out environmental issues (temp/humidity), put some varnish on a sample and put it in a warm, dry place to dry.

 Good luck,

Pat

Not sure which hardener you used, but West System's Fast hardener is famouse for Amine Blush.  Nothing will work on it.  I've expierenced it and it sounds like what you described.

gene t

I used West Systems epoxy with Fast hardener on two of the puzzle joints on my build. I THOUGHT it was fully cured, without blush, by the next day, but 3 days later, it blushed. I did the rest of the project with MAS.

I gave up on waiting for the varnish to cure. I stripped off the varnish with mineral spirits and shoptowels then sanded with 200 grit.  I've been through this before but this time I'm going straight to WS 207 special hardener with UV protection and bypass the varnish altogether. I'll have to think twice about using WS epoxy again if I want to leave the wood bright and varnish over it.

This has happened with both 205 and 206 hardeners

Sanding removes the varnish.  It won't remove the amine blush.  You have to wash that off with warm soapy water.  Sanding it will only move it around and grind it in.  Good luck 

Update. Upon further review, even using 207 hardener, you still have to varnish. SOooo. I scrubbed down the kayak again with scotchbrite and soap/water, then applied three patches of varnish, one Epifanes, one Do It Spar Varnish from Taylor's hardware and one Schooner. No thinner. This time, the varnish dried within the day. So either I didn't scrub hard enough the first time or the thinner was not compatible. I can't believe you have to scrub that hard to get the blush off so I think the culprit was the thinner. Sanded those patches off and applied Epifanes with a brush and no thinner and it dried over night. Not the prettiest coat since I used a foam brush and no thinner so I'll lightly sand this coat and do another roll and tip coat and be done and get the damn thing in the water so I can then work on getting my Haven 12 1/2 in shape for the season. Then on to a full strip planked kayak in the 16 ft range maybe.....