I learned this past week that you should allow yourself enough time to glass the whole side and bottom in one sitting and also allow time to stay with her while her epoxy and glass set. I did the complete bottom on one side of the keel {easy} and 3/4 of the side starting at the bow. Went to bed bragging to my family about how great I was, woke up and went out to check and I had some nasty bubbles/blisters on the side. I've been cutting them out today and was wondering if I need to cut small pieces of glass to go back in the void or if I could just mix up some fairing epoxy and fill them in. Some of them are substancial 8 inches by 1 inch. What do ya'll think?
There are a lot of thoeries as to the cause of bubbles in fiberglassing jobs.Â
One of my favourites is that when resin cures, it generates heat - this heat will warm up the wood causing it to off-gas and form bubbles. Some people suggest fiberglassing in the evening with the wood being warm so that as it cools it actually draws in the resin rather than puffing out gas. Some people will actually intentionally warm the wood and then glass it as it cools.
Try to avoid a circumstance if you can where more heat is being applied by the sun during the first few hours of cure time. I didn't do that and had a bunch of problems and also spent a lot of time playing "hunt the bubbles" - which only works for a short while until the resin starts to set up - minutes on a warm day.
With that said, there are also possible issues with surface prep, wetting, cloth fitting out etc that could have caused these. I had a lot of bubbles in areas where I tried to persuade the cloth to follow a sharp curve and it didn't stick.
For my bubbles I did different things depending on where they were and how big they were. If your resin is still green, you should be able to cut a small slit in the bubble (weaking the cloth but "oh well") and using a bit more resin, push it down - perhaps stapling a piece of plastic jug to it to persuade it to stay in place. For a large, intractable bubble, you will have to cut out that section and fit in a replacement piece. For me - I found a number of bubbles after everything had cured quite hard - the small ones I just cut out and faired the surface with "boat in a can" - aka Bondo.
Out gassing is a function of non-sealed wood. If your wood is sealed (three coats) then it will not out gas.
Bubbles are mostly formed two ways, one is called floating, where a pool of resin has lifted the fabric, but since has leveled out into surrounding fabric, leaving the lifted portion with a void under it. Applying epoxy with a brush and this happens a lot. Another common form of bubble is insufficient wetout, where there just wasn't enough goo in the fabric to make it stick to the substrate. Areas where you started and stopped applying resin are prone to this. Think of these as dry spots. The last of the common bubble issues are physical limitations of the fabric. You'll see these on tight radius areas, where no matter how hard you try, the fabric will pucker, lift up and other wise just not stay stuck. This is a function of the substrate prep, the corners are too tight (small radius) and the cloth just will not lay down. You can staple it, tape it or use a spray adhesive to help in these situations.
As has been mentioned, apply more fabric if the area is large enough that abrasion protection will be necessary or fill as a blemish. Under paint, who's to know.