Marcia Selsor on mon 10 feb 03
Alistair Gillies wrote:
>> This may be a silly question but, can a plaster mold be used to cast
>> plaster? My husband, a builder, says nope, it'll stick. I, on the other
>> hand, am not so sure. Clay shrinks when cast which helps the removal,
>> plaster doesn't so I assume I'll need some type of release.
>
>
I use vaseline as a releasing agent. On things other than plaster, I
find WD 40 is great. I did a large 24" disc last year and the plaster
would not release from the other plaster mold. A friend suggested
heating the outside to warm up the vaseline. I used a heat lamp and
rotated it every 20 minutes or so. It worked. I heard a kathunk from my
work room. The heat lamp did it.
Best wishes,
Marcia in Montana
--
Tuscany in 2003
http://home.attbi.com/~m.selsor/Tuscany2003.html
Alistair Gillies on tue 11 feb 03
>This may be a silly question but, can a plaster mold be used to cast
>plaster? My husband, a builder, says nope, it'll stick. I, on the other
>hand, am not so sure. Clay shrinks when cast which helps the removal,
>plaster doesn't so I assume I'll need some type of release.
Hi,
This is how mass productions runs of molds are made.
There are many ways of sealing the surface, from the recommended 'soft
soap' through other sealants or even WD40 or at a last resort cling film
- there is probably a discussion on releasants in the archives of this
group.
Actually, most soaps can be used but you should mix the soap with a
'little' bit of water. If you do not have a source of soft soap then
washing up liquid can be very good as it is concentrated, but it should
not, for example, be lemon liquid, as the acid will eat into the plaster
and make a rough surface that holds the new plaster [experience!].
The original plaster should not be bone dry, but be damp whilst
'thirsty' enough to absorb the sealant - if it has been above a kiln
then it is too dry as the sealant would be sucked too far into the
plaster, if it is obviously wet then it will not absorb your sealant.
Paint the soap on for as long as you have the patience - perhaps 10 mins
and be patient after you have poured and before your try to release -
the plaster will have cured after 15 mins but wait an hour - and if the
new plaster has gone down the side then scrape around the edges until
you can see the line of the join
Hope that this helps,
Alistair Gillies
Shropshire, England
If you think that I can help more then feel free to email direct.
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