"plaster casting" Topic

Anyone have a good link to tutorials on casting in plaster. I have some plastic packaging that I want to use to make something out of.

Ditto… every time I try i end up with a "thing filled with plaster", or a pile of not-yet-dry plaster that falls apart when i try to release it

Try the Hirst Arts page. link

Three of my own tips:

Add some washing up liquid to the mix – reduces surface tension, fewer air bubbles.
Add some PVA adhesive – stronger, less likely to crumble or shatter as easily.
Add appropriate paint to colour it – then if you you lose a few bits, the broken parts don't show in glaring white.

The biggest tip I can offer is to make sure that you use the right sort of plaster for the application and get the correct amount of water. It is surprising how many people fail to realise how critical the ratio of plaster to water is.

Adding anything to a plaster mix risks changing the properties of the result – most plaster manufacturers say not to add any liquid paint but dry pigment or dyes. Adding PVA to the mix water (no more than 5% – 1-2% will improve strength but not impact resistance) is useful and gives a waterproof result but the castings dry more slowly.

Don't add any more than a very small amount of surface tension breaker to the mix water (a couple of drops in a pint is enough) – using too much can reduces the strength of the casting. Do use a weak solution of washing liquid to rinse the moulds and use them still wet after a quick shake. That does really help with air caught in the details of the mould.

Don't use cheapo soft plaster – get decent hard stuff from a good craft shop or supplier.

If you get crumbling plaster or stuff that fails to set then either the plaster has gone off (i.e. absorbed water from the air & partially set so useless) or you have the water ratio wrong.

You might try googling Alex Tiranti – they have some very good leaflets and may have some on-line tutorials too.

Never has any issues with this stuff.

link

I have cast some very fine and delicate models with it.

Just mix with water until gloopy, added nothing else and bingo.

Use hydrocal plaster, the stuff they make lawn ornaments out of, good and strong and cheap when purchased at home supply stores. I use Rit dye mixed in with the water, use the liquid dye it's easier. Then chips don't show up as white spots. Use chocolate, or orange for different dirt colors.

Mike Bunkermeister Creek
Bunker Talk blog

I've made some small press castings using those clay-like polymers that never harden.

Holds the detail well, can be bent a little to get the original out, as well as the finished plaster castings.

No mold release is necessary.

Just make sure the plaster is totally dry/cured, before removal. I used plaster from a hobby shop.

If you are casting plaster into a thin, rigid plastic form like food packaging, don't expect to get more than a couple of good casts out of it. The heat from the plaster will probably deform the plastic. Either way, you will benefit from using some sort of oily coating- soap, vaseline, wax, etc… to assist in releasing your plaster.

Thanks for all the help!!!!!

@Angel Barracks. Would that resin plaster pick up this sort of detail?

It should pick up that detail. I do see some undercuts but they don't look too bad. Your mold should be flexible. Make sure the plaster sets before removing the casting from the mold.

Matthew

Yes Steve.
I used it back in the early days on my 6mm stuff and it picked up all sorts of details, including the mistakes in the model!

Hobbycraft sells it.

Thanks Mike.

Here Steve, this was made by getting one of my normal wall moulds and casting a resin plaster version:

Once the resin plaster came out of the mould I just bashed it up a bit to make it a damaged section.
You can see all the texture that the resin plaster had on it.

Angel Barracks… can't seem to find a US supplier of that stuff… anything equivalent? (not interested in paying 39 GBP shipping that that site seems to want for one kg of the stuff!)