Casting with plaster

Model Railroader General Discussion (Model Railroader)
1

Has anyone had success making a plaster casting where the cast was quite fragile? I am trying to make a structure whose walls are like a lattice. The lattice members are about 1/8" thick and wide, and each about 5/8 inches long. The mold would be about 4" x 5" with 14 “~diamond” shaped cut outs. It seems to me that it could be strong enough to anchor onto a “wall” once complete, but just getting the structure out of the mold could be problematic without breakage.

Mike

2

Could you do this with resin instead? That would be much less brittle than a hard casting like plaster.

Another option might be to fabricate it with styrene strips, if you’re only making one or two. You could notch the strips halfway through where they meet to get them all in the same plane.

I’ve worked with thin Hydrocal castings from my own molds, and they are very brittle.

3

I use some dental stone. It is much stronger than hydrocal. It is the material your dentist uses to make models of your teeth for the lab. You have to paint it, it is too dense to stain it like you would hydrocal.

4

I’ve cast a lot of fragile plaster parts. I’ve found that mixing Elmer’s glue to the water before mixing it with the plaster helps a lot. It adds strength and I think a tiny bit of flexibility to the plaster.

Here’s a little “how-to” I put together that might help.

http://public.fotki.com/daveinthehat/how-i-make-stuff/casting-plaster/

5

Thanks for the tip and links Dave. I may go with resin, Mr. Beasley. As far as styrene goes, It would require too much work, since the longest piece of styrene would be under 1/2 inch long. I tried to get a couple of plastics companies to mill a piece of styrene according to the drawings and photos I sent them, but they both siad they could not do it for various reasons. The final structure will be almost 3 feet long and 5" tall. If dental plaster is not too expensive, I may also give that a try. Thanks for that tip PhoebeVet.

In conclusion, I’m going to give plaster a try, whether it be dental or hydrocal with a bit of Elmer’s glue mixed into it. If that does’nt work, I will try the resin approach. Thanks again everyone.

Mike