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Hi Mike
Well, if you use a pressure pot and a BIG ASS needle on your gun, crank the pot to 200 psi, then yes, I guess Jeffco does come in a spray bomb, er, can. But I have a better suggestion for mold surfaces and it releases great.
What I would suggest is using Featherfil or Duratec polyester primer for the mold surfaces. You catalyze the same as with polyester resin, i.e. about 4cc/lb minimum of MEKP, brush or sparay and when dry (it's prett fast), wax with Meguires or other mold release wax. It depends on what level of finish you want but if you wetsand with up to 400 grit and polish, it will bring up a great gloss. As you wax, you can see the material soaking in the wax and really making a great surface for realease. I wouldn't use the Krylon since it isn't cross linked and as you saw, only partly releasable. Youcan get the Featherfil and Duratec at car body shops. It is a high build, easily sandable surface that works great for pretty much anything you need a "spray putty" on. The trick is that it has two mechanisms for hadening. The first is that it has a lot of thinner in it that once sprayed, evaporates out almost immediately causing it to turn into putty. The second thing is polymerization. This is the growth of polymers using the 30% or 50% Methyl Ethyl Keytone Peroxide catalyst. After the solvent has flashed off, the liquid plastic turns to a solid. It is then sandable and it does so very easily. So if you have a lot to build up, spray it on and give it a few minutes to flash off then hit it again. You can build up an 1/8" pretty quickly if you need to this way.
If you want a bit more permanent mold, I'd apply a layer or thre of 10 oz plain weave E glass cloth over the Urethane foam, (style 7500). Let it tack up and you can apply the Featherfil right over it, sand real fast and you're done and ready to wax.
And yes, there is a better release wax than Meguires. I use to really like "Finish Kare" a synthetic wax based product but they went belly up. There is another non-wiping off release wax called Chemlease. You want the #41-90 mold release and maybe (if you're belt and suspenders man) the #15 mold sealer. In reality the stuff releases like crazy and I haven't had a problem with just the release. It is simpler than wax in that you wipe it on and let it dry, do it again 2-3 times and you are done. The sealer is applied before that if you have a porous mold. It is in a volatile solvent base so it drys very fast.
I forgot to mention another product that makes great molds. It is melamine finished masonite board and comes in 3' x 7' sections. You can torture it slightly to make a somewhat non-developable surface but you can't do it much. But if the bend is sections of a cone or cylinder, it's pretty flexible. The melamine finish releases easily and just requires a little wax. The basic rule is that if masonite (soft masonite, not the tempered masonite) can do your surface this will. The other benefit is that it's really cheap. I think about $9-10 sheet.
For straight surfaces, use melamine finished particle board. It has a pleasant egg shell finish and if gelcoated is cosmetically perfect and looks like Formica. I have used it inside my boats and it looks great.
I should also mention that those local stiffeners like the newspaper tightly wrapped into a long rope and laminated over stiffens it locally a lot but can leave some print through of where the reinforcement is.
Good laminating!
Dan Newland
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