Ama Menec on fri 27 may 05
Thanks every one who posted on this, your replies have been so useful. I
never thought plaster would warp and Debbie, Jeff and John you're absolutely
right, the first pour has warped. It has a long slow curve to it that
shouldn't be there, and the second poured half is fine, so it has warped
after opening up and being cleaned out, more than 24 hours after pouring the
plaster! Wow, I didn't think that was possible. I had noticed a hairline
crack up to a plastic natch half way along the mould and wondered why it was
there; now I know, it's showing the stress it's under.
I've never seen Hydrocal for sale here in the UK, but I have used a white
Portland cement called 'Snowcrete', I wonder if this is the same thing? I
know a local sculpture company here that casts Herculite mixed with
Snowcrete into rubber moulds to make their sculptures. I think this mix is
50/50 but I'll ask them and check. Would this be a good mix to build up a
mould, adding layers of fibreglass matting as I go to make a say 1/2" to 1"
shell? Maybe thicken the edges to be able to clamp them? Does this sound
like the way to go? Has any one tried Jeff's suggestion of re-soaking the
warped mould and clamping it? Thanks so much.
Less bemused Ama of Totnes.
Email: amamenec@lineone.net
Website: www.amamenec.co.uk
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Debbie on fri 27 may 05
Hi Ama,
To do a lay up mold you need a plaster specially formulated to set very
slowly. Check with your local suppler to see what they recommend for this.
Just for example, I'll mix up a batch of what I use (Forton MG) and be able
to do about a 1/4" thick lay up (several layers of fiberglass matt) on a
model about 2' x 2' before that batch will set off. Two more such layers and
that section is done and just about 1" thick (the first layer being regular
plaster w/o reinforcement). I recommend you make yourself some samples first
to see what thickness & degree of strength will work for your application.
Although I've never tried to force a set plaster mold to change (I do
everything in my power to see that they do not need to be changed!) it is my
understanding that once cured, plaster can't be re-warped.
Best Wishes, Debbie
> -----Original Message-----
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Ama Menec
> Sent: Friday, May 27, 2005 3:20 AM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: 2 Large Scale Plaster Mould Conundrums
>
>
> Thanks every one who posted on this, your replies have been so useful. I
> never thought plaster would warp and Debbie, Jeff and John you're
> absolutely
> right, the first pour has warped. It has a long slow curve to it that
> shouldn't be there, and the second poured half is fine, so it has warped
> after opening up and being cleaned out, more than 24 hours after
> pouring the
> plaster! Wow, I didn't think that was possible. I had noticed a hairline
> crack up to a plastic natch half way along the mould and wondered
> why it was
> there; now I know, it's showing the stress it's under.
>
> I've never seen Hydrocal for sale here in the UK, but I have used a white
> Portland cement called 'Snowcrete', I wonder if this is the same thing? I
> know a local sculpture company here that casts Herculite mixed with
> Snowcrete into rubber moulds to make their sculptures. I think this mix is
> 50/50 but I'll ask them and check. Would this be a good mix to build up a
> mould, adding layers of fibreglass matting as I go to make a say
> 1/2" to 1"
> shell? Maybe thicken the edges to be able to clamp them? Does this sound
> like the way to go? Has any one tried Jeff's suggestion of re-soaking the
> warped mould and clamping it? Thanks so much.
>
> Less bemused Ama of Totnes.
> Email: amamenec@lineone.net
> Website: www.amamenec.co.uk
>
>
>
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