I've read posts about alum, which people say you can apply to wallboard
so that plaster will adhere. This would be in lieu of using blueboard.
All the supplier's I've called haven't heard of alum. Where can I get
it? Is it a powder, you mix with water?

I've also heard of Larsen's Plaster-Weld, for plaster adherence. It's
not cheap, however. A local supplier has it:

1 gal. $23
5 gal. $105

I have no information on it, but would guess that a gallon would cover
250 square feet. I'm thinking of this for plastering certain
non-wallboard surfaces, either finish coats or two-coat.

TIA for any info.

Dan