[ATM] Tool Tiles

["Bill Wheaton" <junkwheaton@gmail.com>]

I'm getting close to finishing hogging my 12.5" mirror (blog and more
videos<http://pythiashat.blogspot.com/>).
It's a little faster than I meant to do, but I am hoping to take that out
about 4 or 5 inches to f/5.5 or as close as possibly can.

I have a few specific questions now that I am at this stage, and possibly a
challange of the state of things.  All of you guys are really good at
sheparding tyros like me, and at the same time getting into some really
interesting conversations on advanced things that I find fascinating to
read.   I'm putting them away in my mind for my next project.

At any rate, I went to Lowes at lunch today and got a 12" x 12" square of 1"
tiles to create a fine grinding tool .  It's been suggested all over the
place to use the "hard" type of tile.  Well, it's all hard as far as I can
tell.  The flat I got is an off color brown-grey porceline with a thin flat
glaze to it -- not white though. Does that matter?  Each tile is very
square, with sharp corners that is, its not rounded like old gloss bathroom
tile.  And its flat -- hardly any texture.  I think it will lay down on my
mirror quite well when pour.  The backing of the tile is a thin pasteboard
mesh in contact with the tile, and a thin fiber open mesh netting - like for
scrubbing, but with holes that are > .1" inch diameter.  There is little
space for fluid flow, and I'm a little afraid if I use dental stone, that it
won't get down in all the crevases if I make the rather thick recommended
mixture.  Am I worrying too much?

Everyone says to use "dental stone", not "dental plaster".  I did online
research, and indeed there are big differences in hardness.  The other
reason to use dental stone is because it has small grain and its purity
won't induce large scratchy objects the way that grout might.

Here is my challange to you all.  Wouldn't concrete poured and vibrated into
the "dam" work as well, and then afterwards use some of that "non-sanded"
polymer grout do the same thing, especially with some of the sealants I've
seen lately?  If not, then why not?  What about a combination -- .5 inch of
dental stone and 2.5 inches of reinforced concrete?

Also, when grinding the tile, won't be as risky of getting big scratchy
things from the tile than from the dental stone?  Or even more so?  Wouldn't
that negate the whole "fine partical" rationale behind using dental stone?

In otherwords, I want to know if the use of dental stone is due to inertial
"we have always done it that way" forces, or if less exotic materials were
tried and found wanting, and how long ago was that, and has technology
changed since then?

Thanks

-Bill Wheaton
Decatur GA.
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