Plaster of Paris


R

rzw0wr

Newbie Switchman
I think I have a misconception of Plaster of Paris.

First, I thought dried PoP would dissolve in water.
This appears not to be true.

I also thought PoP was father soft when dried.
This also does not appear to be true.

How hard should PoP be when dry?

I made some plaster cloth with PoP and put it on my layout.

The only way I can sand it smooth is with my orbital sand and 80 grit pad.

It is also very hard to sculpt when dry.

Any information on PoP would really help.

This stuff is about as hard as the Hydrocal I have.

Dale
 
It's still a gypsum-based product. It does bind with water, not dissolve in it. It's not like salt or sugar. When it mixes, there is a slight exothermic reaction and the mold will get warm to the touch. It can be placed where you want it when it is still damp and cool to the touch, but only carefully. At that time, some carving can be achieved.

Yes, it gets very hard, but not as hard as Hydrocal. In order to sculpt it, you must use abrasive tools or hard ones with edges where you are willing to make repeated strokes to achieve the depth and look you want in relief. Or, use a rotary hand drill with a suitable bit and abrade away what you don't want that way. It will be dusty, just like sanding drywall.

Most people craft their own moldings and pour PoP into those. You can use a good quality of aluminium foil, for example, and crumple it into a vessel. When your PoP has cured, peel away the foil and you will have your rough stone face.
 
I like hydrocal for the reason it stays green longer allowing for more time to carve what you like before it's rock hard.
Whatever you do use be sure you mix a little paint into the mix so it's a colored plaster when dry. If it chips it looks like snow in a spot and not really nice.

Dave
 
Like hyrocal, keep the Plaster of Paris container tight to prevent moisture from over time ruining the material. I lost a lot of hyrocal and Plaster of Paris by not storing the material in an air tight container between use.

I also found that there are different grades of Plaster of Paris. Some are intended for patching and others for modeling and crafting. Avoid the patching grade typically found in hardware stores.

I never tried it, but some modelers have suggested to add a little vinegar to the Plaster of Paris to reduce the material's setting time. I'm not sure of the amount to add, perhaps other forum members have tried adding vinegar to Plaster of Paris and can add some adding information.

Thanks.

Greg
 
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