Here is a quick run down of how I make most of my molds. 1. Start with a good finish on the plug you are going to make the mold from.
2. put a minimum of three coats of good old Johnson's paste way. Apply each wax coat in a different direction and use old flannel bed sheets to buff out. 3. Spray on one or two coats of polyvinyl alcohol (PVA) 4. All of my molds are epoxy/glass and I use West Systems epoxy with the fast hardener. 5. Mix up the epoxy for what will be the mold surface. I start out with a batch of West systems and add red pigment and about 10% by volume of Cabosil. The pigment makes a nice uniform color mold surface and the Cabosil thickens the epoxy somewhat and makes it stick to vertical surfaces easier and also hardens the surface somewhat. 6. brush on your red jell coat and make it a fairly heavy coat. Let cure before continuing. 7. Scuff the jell coat with a scotchbrite pad so the following layers will make a good bond to it. 8. All of the fiberglass used in my molds is fiberglass matte. I don't use any woven cloth. Doesn't matter where you put it in the lay-up if there is any woven cloth in the mold it will eventually "print through" and show show up in the surface of the mold. 9. I tear the fiberglass matte into manageable squares and carefully pull it apart so that each piece is half of its original thickness. Any cut edges have a tendency to show up as fine lines in the final mold surface. I know epoxy isn't supposed to shrink but "print through" is a problem. That is why I always work with torn edges and very thin sections split from the original matte. 10. Buy a box of 1" throw away chip brushes at Harbor Freight Aircraft Supply and start applying the torn sections of matte and saturate with epoxy using the chip brushes stippling out the air bubbles. It is fairly easy to see the air bubbles against the red gel coat. Tear the pieces as necessary to fit around sharp corners, etc. Keep applying matte until you get at lease about an 1/8" lay-up over the complete surface. I generally don't go much thicker that 1/8" to 3/16". 11. I generally trim the excess matte from the mold when the glass has reached the leather stage. Leave the mold alone until it has cured at least twice as long as you think it needs to be completely cured. 12. To pop the mold from the plug start with some wooden wedges and work them between the mold and the plug. Compressed air does a great job of helping to separate the mold from the plug. If you waxed the plug well, and have a good coat of PVA, you should be able to pop off a beautiful mold. 13. After you have your mold separated wash it down well with dish washing detergent. If the phase of the moon was correct you should have a mold ready to lay up parts in. If not, sand the mold surface finishing up with 2000 grit wet or dry sandpaper and polish out with rubbing compound finishing up with white polishing compound. 14. Wax the he** out of the mold using the same Johnson's paste wax. When you think you are done waxing think about how you are going to feel if you ruin it by sticking a part in it and put on some more wax. 15. Be sure to spray a coat of PVA on your waxed mold before you do your lay-ups. Remember a green mold is a lot easier to stick a part in than a well used one that has been waxed many times. Wax and PVA are your friend here. THis is just to give you an idea of how I make my molds. THere is no substitute for experience. Dive in and try it on a smaller part and don't be afraid to experiment. Some things will work and some won't but you will be learning. Steve Eberhart skp...@charter.net wrote: > I have a question on building molds. > My experience with mold makeing for fiberglass is that the mold (if made > of fiberglass) needs to be at least twice as thick as the piece you are > going to make. So, the heat from the part wont warp the mold. > > 1. What type of material is being used to pull molds? > 2. If making of glass how thick and are you using a spray on release agent? > Molds I have made before have been from. Glass, Sheetrock mud, plaster > of paris, paper machae, clay, even concrete. I just want to know what KR > people are doing. > > Steven Phillabaum > Auburn, Alabama > > _______________________________________________ > see KRnet list details at http://www.krnet.org/instructions.html >
