reelnmn Posted April 25, 2006 Report Share Posted April 25, 2006 I've been experimenting with plaster molds for awhile now. But all my top halfs end up being extremely chalky. Also you can dent them by applying a small amount of pressure. Any ideas on what would cause this? Quote Link to comment Share on other sites More sharing options...
Senkosam Posted April 25, 2006 Report Share Posted April 25, 2006 You have to coat the top surface and cavities with something that will withstand heat and moisture. I use Valspar, others use epoxy. Quote Link to comment Share on other sites More sharing options...
jm Posted April 25, 2006 Report Share Posted April 25, 2006 What material are you using? Most of the "plasters" have portland cement in them. This material forms a chemical bond with the water. I think this is called "hydroset". Anyway, if there is not enough water, the surface will dry out prematurely and chalk. I always try to keep a new mold wet for about 24 hours to be sure that there is enough water to form a rock hard set. One clue is that the top half is the one that chalks. If you bake both at the same time, the top one is the one that was cured for the least time. Keep it moist for another day, then dry it. hope it helps jm Quote Link to comment Share on other sites More sharing options...
nova Posted April 25, 2006 Report Share Posted April 25, 2006 Here's a question. Has anyone ever used hydralic cement to make a mold. It says on the bucket that it doesn't shrink and sets really quickly. Quote Link to comment Share on other sites More sharing options...
reelnmn Posted April 25, 2006 Author Report Share Posted April 25, 2006 jm, I'm using Plaster of Paris from Home Depot. You've given me an idea on why I'm getting so much chalk... I'll try the 'fix' and report back. Quote Link to comment Share on other sites More sharing options...
jm Posted April 25, 2006 Report Share Posted April 25, 2006 reelnmn Plaster of paris is a little bit soft to start with. Try Durham's, or if you do a lot, go get a bag of ultracal 30. These products have a little more portland in them, and set up real smooth and hard. hope it helps, jm Quote Link to comment Share on other sites More sharing options...
reelnmn Posted April 25, 2006 Author Report Share Posted April 25, 2006 Does Durhams or the Ultracal give better detail than plaster of paris? Where can i pick them up? Quote Link to comment Share on other sites More sharing options...
jm Posted April 25, 2006 Report Share Posted April 25, 2006 Durham's Rock Hard Water Putty should be available at Home Depot, or Menards, or a hardware store in small quantities. Ultracal 30 is specificially designed to capture fine detail in a hard casting. Get it at a serious art casting outfit, or here http://www.plaster.com/Ultracal.html hope it helps, jm Quote Link to comment Share on other sites More sharing options...
