Message text written by "BP - \"Is this the list with all the ivy
haters?\""
>Actually, I'm pretty sold on Rockhard for small plaster repairs. It's a
gypsum-based mix anyway. It's convenient but expensive compared with a 50
lb. bag of plaster patch. It doesn't shrink on small repairs that I've ever
noticed.<

My first serious chemical engineering job, 26 years ago, was with a little
outfit which now goes by the name USG, and so I've seen a little gypsum in
my time. For a while I was seeing 50 tons per hour of it. There are lots of
interesting things about gypsum, more than I will ever know, but a few
things I do remember.

Gypsum plaster doesn't shrink, it expands. Gypsum remains water sensitive
and should not be used outdoors unless you live in the Gobi desert. You can
make gypsum stronger and more weather resistant if you mix it with Portland
cement, and indeed, all portland cement contains a little gypsum. As for
feeding it to the parrot, this may be a better idea than anyone imagined.
There is a series of products USG sold under the Hydrocal trade name which
was gypsum plaster treated in an autoclave with acid. The product was
harder than concrete and was used as bridge deck repair mortar prior to
topping with asphalt. Lousy adhesion, though. 

As for mixing latex paint with repair mortar, that sounds like one of those
stunts audiences should be cautioned against trying themselves at home.
Latex modifiers for cement are not the same as latex paints, and results
using paint would be highly unpredictable.

 Mike E.