Re: [ATM] Dental stone for tool

[Mark Holm <mdholm@telerama.com>]

Making the dental stone tools is so easy, I can't think of a good reason
not to make one, with tile, for grinding and one, without, for a lap base.

Elite Rock is a product of Zhermack  http://www.zhermack.com

Water / Powder ratio 19-20 ml/100 g
Mixing time (by hand) 60”
Mixing time (under vacuum, 240 rpm) 30”
Working time 12’
Setting time (Vicat) 14’
Setting expansion (2 h) 0.08%
Setting expansion (48 h) 0.19%
Compressive strength (1 h) 52 Mpa (530 kg/cm2 – 7.542 PSI)
Compressive strength (48 h) 81 Mpa (826 kg/cm2 – 11.748 PSI)


Zhermak also makes Elite Stone

Water / Powder ratio 23.5-25 ml/100 g
Mixing time (by hand) 60”
Mixing time (under vacuum, 240 rpm) 30”
Working time 8’
Setting time (Vicat) 14’
Setting expansion (2 h) 0.08%
Setting expansion (48 h) 0.09%
Compressive strength (1 h) 42 MPa (428 kg/cm2 – 6.092 PSI)
Compressive strength (48 h) 60 MPa (612 kg/cm2 – 8.702 PSI)


and Elite Model

Water / Powder ratio 28-30 ml/100 g
Mixing time (by hand) 60”
Mixing time (under vacuum, 240 rpm) 30”
Working time 7’
Setting time (Vicat) 12’
Setting expansion (2 h) 0.04%
Setting expansion (48 h) 0.07%
Compressive strength (1 h) 29 MPa (296 kg/cm2 – 4.206 PSI)
Compressive strength (48 h) 62 MPa (632 kg/cm2 – 8.992 PSI)


These each come in various colors.  The color won't matter too much to you.

I think I would go with the Elite Rock for it's higher strength and
longer working time.  It takes longer to mix up the amount you need for
a tool than it does to mix up the small amount dentists need for a model
cast.  7 or 8 minutes working time is not much.  12 would add
significant margin.

Mix vigorously for 5 or 6 minutes, pour, shake to rough level, poke down
your tiles with a bamboo teriake skewer to make sure they haven't
floated up, shake once more, then let it set up.  When it feels
reasonably hard, unmold, take it out to your driveway and grind the back
flat against the concrete with a bit of water for lubrication.  Don't
forget to bevel the back edge against the concrete too, your hands will
thank you later.  No need for epoxy, polyurethane or any other sealer.
By avoiding that, you make up some of the expense of the dental stone,
and save time and a smelly, sticky job.

See more thorough, illustrated instructions at
http://www.gotgrit.com/make_tool1.php?osCsid=501d4d3bd04d7b5655c039eca83f3325
click the Next Page links to progress through the tutorial.  The only
thing it doesn't mention is the water amount.  Try to be close to what
the manufacturer recommends or a bit more water.  Add the powder to the
water, not the other way round, and stir like crazy.  You will need a
strong stirring stick.  I used a plastic paint stirring stick.  Add
powder and mix till it is about the consistancy of very thick, stick
mud, the kind you have to work hard to scrape off of your shoes.  Have
everything ready in advance and work fast.  Remember that 12 minute
working time.

It is a lot easier than it sounds. After my first time, I was almost
giggling over how easy and quick it was.

-- 
Mark Holm
mdholm@telerama.com

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