How to clean mold release off plaster mold for Slip Casting??

[Emeraldmaker]

I'm making slip cast molds from pottery plaster #1 from a wax original.. I've always used clay originals before without this problem and the wax Sculpture details are grabbing chunks of the plaster when demolding. (waited 24 hrs for cool plaster to demold). 

What can I use on the wax as a release agent that won't inhibit the absorbtion of plaster later?? I looked into pure lube/potters soap/green soap but saw that bonds permanently so can only be used on mold seams, I have petroleum jelly that I normally use to release the seams, but am wondering if that will seal the inside and create absorbtion issues.. Same with Murphys Oil.. 

I saw someone mention cleaning with vinegar? Will that work for petroleum jelly or Murphys oil??? 

Thanks! 

[Min]

Vinegar works well for cleaning mold soap off the plaster. I think the plaster is probably softening the wax as it heats up during the curing and that's what is causing the chunks of plaster attached to the wax. It's just getting too hot.  Plaster does expand ever so slightly so I've found it's best to remove whatever is being cast as the plaster is cooling down rather than waiting until it's cooled right down. Mold soap / Murphy's oil / mold lube etc don't bond permanently, sealers do though.

[Chilly]

Interesting.  I have a list of what to use as mould release for various master substances.  Wax is not on the list.  Wood, which is absorbent, says one coat polyurethane, two coats soapy release.

I think @Min is right about it heating up as the plaster cures.  Vinegar works great at removing mould release.

 

 

[Mark C.]

Use pure lube on the wax orginal-its made for that and will not get into the paster.You can coat any item before pouring the plaster .Green soap will also work

stay away from oils-like petroleum or Murpheys

[neilestrick]

Plaster molds are not typically made directly from the wax original. I would consider making a silicone rubber mold from your wax original, then make a plaster model from that, and then make your plaster mold from that. It's a couple of extra steps, but you'll avoid the problem of the wax softening and get a better looking piece in the end. Plus you'll have a rubber master mold that you can make more plaster molds from in the future.

[Stewart Smith]

It's been awhile since I used plaster, but when moulding off wax I'd splash on a thin surface coat of plaster, then let that set up some.
Then do your main plaster mix and pour on. This will ensure the detail on the surface of the wax and it won't matter how hot the rest of the plaster gets. Of course, the law of making moulds requires that unreleased surfaces will not stick and that carefully released surfaces will stick forever. so don't let that surface coat set too long, or the layers of plaster might want to separate.