Clay plug building question

So I am planning to build a plug and (from that) mold with a process similar to that in this video:
http://youtu.be/dBoXmqG5YBQ
The differences are that the plug will have a large melamine flange (for infusion) and I would like to use clay instead of sheet wax to create the necessary gap. This will be my first time working with clay to this extent and I am not sure which of the MANY options out there will roll out to a 1/4" thick sheet and conform well but still be hard enough to support applying the surface coats and fiberglass mold. Any tips on choosing the right clay (before I buy 40lbs) or what to expect from this plan would be greatly appreciated.

Hi mattman, any idea what he’s brushing on / wiping on @ 0.57 sec

I may not be following you corrctly but why don’t you just build your plug to the finished size?

It might be PVA. When I create counter molds with sheet wax, I use PVA to act as a release.

Roger, like in the video, I have a part to start from that I need to create a slightly oversized/offset shell of. The clay (like their sheet wax) is being used to oversize the original part.

After a lot of reading I am inclined to go with WED clay for its affordability and ease of use.

Gotcha. I can’t really help with the clay questions. I had to look up WED clay. It’s certainly cheap enough although I don’t know how well it will work as a calibrating material. Good luck with the project. Post when you do it. I’d like to hear what you have to say after using it.

I have no experience working with WED clay but i’ve worked with sheet wax just like what the guy is using on the video. the only difference is that after applying the wax i apply a layer of clearcoat so that i get a smooth layer which i can then apply my release agent on. hope this helps. note that you can get sheet wax in different thickness. try http://www.freemansupply.com/

What is that on 1:09 he is brushing? Resin with coloidal silica or something else?