Re: ATM 18" mirror Progress and Dental Stone question

["Herb Kasler" <h.kasler@worldnet.att.net>]

Ken,

FWIW, you can make a perfectly good tool without getting dental stone. The
folks at the Chabot workshop here in the Bay area use plain old concrete,
sealed with marine epoxy. They've made countless mirrors with it.  I used
something called pourstone, which is a cement for anchoring fenceposts, to
pour the tool for my 16" mirror. I sealed it with polyester resin (the stuff
you get for marine fiberglass) to keep any gritty bits from escaping and to
adhere the tiles to the face. The stuff is just a mixture of portland cement
and plaster of paris. It is really, really hard. You won't be able to break
it unless you take a sledgehammer to it or drop it off a 5-story building.
It also resists moisture quite well, though the sealing makes that a moot
point. I had no problems with it whatsoever.  I bet you can get it at just
about any hardware store in Australia, and it's a lot cheaper than dental
stone, too. I paid $20 for enough to make my 16" tool. You might have to buy
another $5 worth to make your 18"er. In the time it would take you to get
your dental stone, you could be done grinding.
Later,
Herb.