: I have tried something similar using plaster of paris and found that the
: plaster soaked up the epoxy when I tried to lay up carbon fiber inside the
: mold. Does Ultracal have better properties that solve that problem, or
: do you have to treat the mold with something to seal it?

Hi Dan,

Ultracal is very hard and expansion is nil. I use to buy it in 50 lb bags at lumber yards in large cities. All plasters must be sealed. I'm from the old school and used several coats of shellac until the surface is shiny. Let each coat dry well before putting on the next coat. Lacquer is also good as a sealer. The surface must be shiny. Then put on several coats of green poly parting. This comes in a water base or lacquer base. Then three coats of paste wax and shine each coat. I use a spray mold parting after this but its not necessary. When you seperate your model from your mold, besides prying and beating on it you can take compressed air and force it in a seam and seperate them.

Take care
John