Quote:
Originally Posted by vfrrider
What it sounds like to me is the vacuum is degassing your epoxy.
To avoid this, place mixed epoxy (just use one container and mix thoroughly) in a vacuum chamber (an upside down glass cooking pot on a table top with a hole for the vacuum line) and pull a vacuum for a few minutes, say 5, to take out your air bubbles.
Now coat fiber on the mold and press resin into weave. Easy way to cover for vacuum is to use 2 part cover with a bead type seal. Smooth well, seal. Pull vacuum and let set. You SHOULD get little to no bubbles, no air left to outgas. Thats why prepreg works so well. Optimum concentration of resin and no air. Just remember, all vacuum baggin does is remove air for optimum resin penetration and supplies its own pressure for mold following.
Finish as before for shiny coat, or leave dull for racer look.
Larry
VFRrider
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+1 for the degassing, what is happening is that there are microscopig bubbles present in the resin mix but they are next to invisible at ambient pressure but once you place it under the vacuum these bubbles enlarge obviously because of the decreased pressure. What seems to be happening is that you have not yet achieved suffecient vac to allow for a large enough motive force within the resin to pull the bubbles out and not just have then sitting there as the resin cures. There is never too much vacuum, even under full vacuum you will only achieve about 33% resin content (which is ideal) and that is if you are infusing... more pressure is possible in autoclaves and compression molding systems.
Also make sure that you have enough slack in the bag, don't jsut rely on the "stretchyness" of the bagging, it is not nearly enough....
Don't worry you guys sound like you are well on your way.
hey mrgrn..... tune in there is some decent info on here and it might remedy your issue of porosity aswell
