A few questions about sculpting on top of plaster

Hey there, I'm working on my first sculpt and have run into a few things I have questions about.

I'm working on making a Deatheater mask from Harry Potter. I used tinfoil to take a negative impression of my face, then poured plaster of paris into it (so that I could have a good base to work off of - like I saw in SpaceCowboy's http://www.therpf.com/f62/pota-inspi...-masks-144349/ post.

I made sure to wipe as much of the vaseline off as I could before sanding, and waited until the mask was cool to the touch (5 hrs, and I allowed it to sit in the sun to help it cure) before starting to sand. But as soon as I started sanding, I noticed the pad on my sander was coated in an almost wet layer of plaster.

I'm wondering if I should have left it to cure longer or if the vibration from the sander (it's one of those Corner Cat detail power sander things) re-liquified the plaster somehow? Has anyone run into this before? I got it smooth and then set it back out in the sun in hopes it would dry out some more, because I don't want to start sculpting on top of it while it's still feeling damp.

Second, I was wondering if when using clay (either Super Sculpey or Chavant NSP, I haven't settled on one yet) it was necessary to seal the plaster with like, a coat of primer or something, or can I just put the clay right onto the plaster?

I eventually want to do a silicone mold and do resin pulls, if that helps...I'm just wondering what is up with the plaster? Any ideas or tips and tricks? I'd appreciate it a lot. Thanks everyone...

Your plaster was just not cured. If you poured the plaster into the negative of your face, rather than brushed in a thin coat, something of that thickness can take quite a while to fully cure. Couple of days probably.

The plaster won't affect Chavant NSP any, though it might be a good idea to seal it anyway, just to make it easier to remove the clay afterwards. I hate sculpey, so can't advise you there...

You can kinda 'speed dry' hydrocal (if that's what you used) by putting it in an oven set real low (100-150 max). You'll know when its getting dry because it will lighten (weight) a good bit.

It's been so long since I did anything with plaster, I didn't think to let it cure longer than the old 'make a handprint in sand and fill the void' crafts of days gone by. Makes sense. I'll let it sit for a few days before I try doing anything with it.

And thanks for the tip about the oven. If I get desperate (or if it refuses to dry, which with the SURPRISE NEVERENDING RAIN we've decided to get to up the humidity) I may try that. I appreciate it!

As for sculpting on top, remember whatever you use cannot have a sulpher base or the silicone won't set. I love Super Sculpy, but if the area that is to be built up will be more than a half to three-quarters inch thick Super Sculpy will crack when you bake it.

Do you want to keep it so you can take several moulds off it, or were you thinking just one silicone mould? If you just want to sculpt, mould, mother and cast, then you could use sulpher-free plasticene or clay. Probably cheaper, too.

If you want to do something up that will last, maybe ApoxieSculpt or even plumbers putty - something that sets up on its own.

As for sealing it, I'm meh on that. We did a Vincent mask and just slapped the Roma Plastanina on the plaster.

I picked up something called Plastalina (by Van Aken) that is sulfur free. I'm looking at probably just one pull of a silicone mold and then make a mother. It seems like it's pretty firm - I'm not looking for SUPER sharp details that I'd need to machine in.

The plaster seems to be drying better as it sits, so I think it'll be okay without sealing it by the time I actually get around to breaking out the clay (Sunday).

If you have trouble with the clay sticking to the plaster, put a little vaseline (petroleum jelly) on the surface. the clay will stick better. Also you can heat the first layer of the clay so it grabs better. This works if the plaster is either too wet or too dry and powdery.

I'd definitely recommend Aves Apoxie Sculpt. It's a two-part self-hardening resin product that works somewhat like super sculpey firm, but doesn't need to be baked. The trick with it is to get the shape right, smooth with water, then let it sit and then you can do detailing - if you do that too soon it will be like trying to work through a plastic bag and you'll get curved impressions instead of scribed lines, as it is rather elastic and sticks together while curing.