More info: there were no bubbles my first time out. Something unknown caused them to form.

Anyone?

Can you send me some pictures of the affected areas? Can you tell if there is air or water within the blisters? I am also concerned about what is happening and hope that we can get to the bottom of the issue.

Thanks for your concern Joey. The bubbles are filled with air and seem to be in a straight line, which is perplexing.  Here are some pictures.

Looks like someone dripped some kind of liquid contaminant on the wood prior to glassing. Like oil or something else that caused adhesion problems.

Cheers, Pat

Pat may be on to something. Possibly surface contamination or just plain old poor adhesion. Since there is no water in them, I would not worry. Could be that the air was always trapped and caused a blister once warmed up by th sun.

The fix is simple, grind the blisters off and patch the area with cloth and epoxy. 

Thanks!

I already put a coat of varnish on. Can I epoxy over the varnish? 

If it wasn't something dripped on the plywood, perhaps there was some contaminant on the FG cloth... perhaps tape on a roll of FB? Just a guess.

re epoxy over varnish... I would sand it off and put epoxy on epoxy, sand when cured and then varnish over. However, fix the bubbles first. Cut the bubbles out of the cloth with a sharp knife, or carefully use a rotary grinding tool, and then apply epoxy and a small FG patch. But... if you are have already varnished the areas, perhaps wait until further work needs to be done.

Nice WD! I had a similar thing happen on the bottom of my hull, but before I was done building. These guys are all right on about the soultion-you must grind down the bubbles, and recoat with epoxy. It doesn't look too large or widespread that you'd compromise strength very much, but you can add a small piece of fiberglass cloth if necessary. It looks like you have a good, solid fillet built up. This is wat it looked like when I" mce_src="" alt="" border="" hspace="" vspace="" width="" height="" align="" /> sanded a bubble out: