Metal Casting Zone

Here is a cut and paste from my "New members" entry:

I have been using lost foam white polystyrene which I paint with "Mud". In my case I use a mixture of tile adhesive and emulsion paint because that is what I happened to have on the shelf. (Works well) I have a problem in that the mud penetrates the interstices of the foam, and these microcavities are then replicated in the surface of the casting. Applying masking tape to the surface of the pattern solves the problem but is cumbersome. Blue foam gives good finish but needs hotter pour to ensure burn-out. Does anyone have a better idea that masking tape for white foam?

unfortunatly i think anything other then tape is going to fill those spots in the same fashion. I use plaster of paris or that drywall mud plaster. neither of those will solve your problem though.

Hi Mike.

Thanks for the reply.

Having posted my question, the old mind started grinding slowly around this topic.


Thoughts........ wallpaper paste is largely cellulose. It would run into the foam interstices, but I wonder if it would then burn away with the foam? If so I could first seal to a smooth surface with paste and then invest with "mud". (Two drying out sessions instead of one of course.)

I must try it.

I like the thought. definitly worth trying.

depending on the intricities of your design maybe you could use that shirking window plastic under the plaster? It would burn out nasty but then your errors in the surface would be extra metal that could be taken off.

I had thought about trying tissue paper, like they wrap breakable stuff in for your wife.
Lay it over the foam and lightly spray some water on it and smooth it out. Once it dries, put on the drywall compound. When I did some model airplanes, the tissue on the wings would shrink and get tight. I don't know if it was the same tissue paper or something special.

Thanks Jammer,that's a good one. I have some tissue from my model aeroplane department.
I will give it a try.

Mike
I've had good luck using bee's wax. Warm in a double boiler type heater. When it's about the consistency of gravy brush or trowel it on your pattern (depending on detail).
If some areas don't appear as you'd like,wax can be smoothed with the heat of your fingers. I guess this is using both lost foam and lost wax together,ha,ha....

Hi Blindpig.

That's a great idea. Thanks. I will give it a try.

I keep bees...........