Re: [SGII] Modular Starship Terrain AND CASTING

>I just bought a couple of pounds of Polytek - Plastil 71-30 Silicone
>RTV and it is heat-rated enough to work with melted lead...

Yep, this is the same stuff I picked up this last weekend.  I have yet
to 
bust the seal on it though.  I am REAL, REAL cautious about new
techiques.  
Especially when I get only one chance to do it right, and it will cost
me 
$5-10 a shot.

It's not a fortune, but then again I am pretty 'anal' about some things
(I 
am told <g>).  Heck, I just re-built one of my masters last night
because I 
did not like the way the seam was going to lay in the first one.

That is another thing.	I am new to this casting stuff, and one of my
first 
molds is going to have to be a two part mold.  I have read how to do it 
(about a dozen times), but I am still a little worried that I have no
way to 
de-air my RTV or my plaster when I cast.

Do you de-air your RTV, plaster or resins before your use them?

>This assumes you don't have an inside line on some good cheap resin,
>of course.

The prices I can get locally are about two or three times (or more) then

what I will pay for my dental plaster.	From what I hear the right kind
of 
dental plaster can be thrown against a concrete floor and not crack. 
It's 
drawback is that it is heavy and more expensive than PoP.

>And if you use some kind of mould-release, it can help the mould life
>quite a bit.

I will be using Vasiline.  I have been told that if you heat it a bit
and 
rub it on it works well.  And it is dirt cheap.

>Now, having rambled on about all that, if you *like* your dental
>plaster and if it's good for the purpose... tell us about it!	Let us
>know how it goes.

I have yet to pick up the dental plaster, but again from what I hear it
is 
what I need.  I do I will let you know.

Scott Clinton
The Grumbling Grognard

>From: adrian.johnson@sympatico.ca
>Reply-To: gzg-l@csua.berkeley.edu
>To: gzg-l@scotch.csua.berkeley.edu
>Subject: Re: [SGII] Modular Starship Terrain AND CASTING
>Date: Tue, 16 Oct 2001 02:54:18 -0400
>
>The plaster I have here is labelled "LePage's - Poly - Plaster of
Paris".
>I've done plaster terrain bits, and it's worked fine.
>
>My caveat:  don't bang them around too much.  They will take some
abuse,
>such as found in normal play and decent storage.  If you toss them off
a
>table onto the floor, they *might* break or chip.  If it cracks, you
can
>glue it and repaint - not difficult.  If it shatters, well, make
another 
>one.
>
>These are *not* as strong as a cast resin piece, but a *lot* less
>expensive.  I'm satisfied trading off the strength for the cost, and
then
>taking a bit extra care in the "care and feeding" of my terrain.  If
your
>wall sections are really thin, you might want to stick to resin, OR use
a
>reinforcing method such as glass fibre, plastic mesh (like you'd use
for a
>window screen), gauze, etc.  That will at least stop the part from
>shattering all over the place if it drops from too high up or at a
funny
>angle.  Also, as I said before, depending on the size of your piece,
the
>plaster sets up to a point that you can demould pretty quickly.  While
I've
>got some odourless 2 minute resin, that stuff costs a bundle.	Some
other
>non-stinky resin I've used in the past is great and available in large
>quantities, but is pricy and takes up to 24 hours to setup properly
(unless
>you boost the reaction by cooking it, but that's tricky to do properly
-
>you have to use a hot-air "oven" or the temp gets too hot).  And there
are
>resins available like polyester resin for fibreglass, commonly
available
>all over the place, but it stinks a LOT to use and is hugely toxic.
>
>The plaster hardens with an exothermic reaction, but won't get hot
enough
>to damage your moulds unless you have unusually soft RTV (or RTV with
*lot*
>heat tolerance) UNLESS you make huge parts that are very thick masses
of
>plaster.  Then the heat can build to dangerous levels.  For the kind of
>stuff you're talking about, you won't have a problem.
>
>I just bought a couple of pounds of Polytek - Plastil 71-30 Silicone
RTV
>and it is heat-rated enough to work with melted lead, so for plaster
it'll
>be fine.  I imagine that is going to be common to a lot of the stuff
>available.
>
>This assumes you don't have an inside line on some good cheap resin, of
>course.
>
>And if you use some kind of mould-release, it can help the mould life
quite
>a bit.  If you have a plastic supplier anywhere nearby, you can check
and
>see if they carry a spray-can type mould-release suitable for RTV. 
Though,
>I've done a bunch of resin casting with my 2-minute setup stuff (great
for
>hobby purposes - it's odourless, it mixes in a 50:50 ratio so it is
*easy*
>to measure accurately, and you can demould in 2 minutes or less) and my
>moulds are all ok without using mould-release at all.
>
>Now, having rambled on about all that, if you *like* your dental
plaster
>and if it's good for the purpose... tell us about it!	Let us know how
it
>goes.
>
>
> >From: "Scott Clinton" <grumbling_grognard@hotmail.com>
> >Subject: Re: [SGII] Modular Starship Terrain AND CASTING
> >
> >>...plaster actually labelled "Plaster of Paris" on the container is
> >>what you want.  It is used for outdoor garden statues and
> >>architectural mouldings, so it is quite strong.
> >
> >Hmmmm, I did not realize PoP was that strong.  I was intending on
using
> >dental plaster.  From what I have seen it is very strong and it is
also
> >cheaper than resin (and a lot easier on my molds).  I can get the
dental
> >plaster pretty cheap, but it is still a bit more than PoP.
> >
> >I have two masters done (both walls) and got my RTV...making
progress.  
>:-)
>
>
>
>********************************************
>
>Adrian Johnson
>adrian.johnson@sympatico.ca
>

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