Blisters . . .
Posted 01 February 2013 - 06:16 AM
Yes, I know that rule, and have been building boats for decades, but temptation got to me. Air temps are wild this year - days in the 40s and then days in the 70s. And my shift work schedule is kind of wild, so the other day I have to be at work at 11, the glass is draped on the kayak strip deck, and it will be the last warm day for a week! Hot dang! So around 8 I mix the goo and get to work. Oh yeah, a bit of out gassing, so I police bubbles. About 10:30, the resin is now pasty sticky, I go around and police a few remaining out gas bubbles - off to work.
Shortly after 6 I arrive home - garage door grinds up and I go WHAT! Blisters all over the deck. Multiple factors contributed to this mini-disaster: I violated Rule #1. I left for work so I wasn't around to continue bubble policing. To shave a few pounds I used a 3 1/4 oz tight flat woven cloth that only had little pin pricks of open space between the threads and that apparently sealed the air under the cloth causing it to raise a blister. The 4 oz I have used has a more open weave and air goes through it.
On the upside, the resin formed a meniscus at the edge of the blister so a few swipes with a carbide scraper and the raised part of the cloth fluttered away. A few more swipes feathered the edge, ready for patching. So today I patch. Then scrape the patches, add a coat of resin, sand, etc etc . . . What a PITA . . .
Next time the plan will be, stoke up on coffee when I get home from and hit it while the temp is falling.
Posted 01 February 2013 - 08:55 AM
PITA pretty much describes it........once you get past the "WTF!!!!" stage.
Have never heard this one discussed as a possible solution, but in the age old debate of which to do first........epoxy coat.......then glass vs. apply glass to bare wood.............the notion of preventing the outgassing has merits for the "epoxy coat first" crowd. Provided you scuff sand as soon as it hardens enough to do so, you should easily achieve a chemical bond for the glass coat. Don't know if you can still get outgassing through an initial coating of epoxy.
The only other solution I've come up with to avoid outgassing caused by changing temps is to really crank the heat up on the project well beyond what it is going to be in, so no matter what else happens, it will be in cooling mode, working to create more of an internal vacuum to draw in the juice vs. hot air expanding and outgassing through it. The problem with that, in some areas, is the project will be hot enough to kick the epoxy before you want it to.
Posted 01 February 2013 - 11:00 AM
Out gassing is usually only a problem with raw wood coatings. If the surface has received prior coatings, the cellular structure is sealed and out gassing isn't typically a problem. This said, if you have wide temperature swings, you can have gas expansion issues, under fabrics, veneers etc., where the air trapped in the goo during mixing or application (fabrics, veneers, etc.) can expand enough to cause a problem. As you and any experienced goo worker knows, it's a simple rule - make sure the temperature is relatively constant or descending, until the epoxy has no tack left. I use those oil filled heaters, you can get from Wal-Mart for 20 bucks and if necessary toss a tarp over the project, to tent the heat in. Come goo time, I can insure the temperature is falling, just by removing the tarp or turning down the thermostat.
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