How to Make a Plaster Mold
Here's how we made our plaster molds.
Supplies:
* Drop sheet for painting. We cut ours in half so can use the other half later. This is to cover the work surface and can be thrown out later (had plaster spillage etc). I try not to make waste like this but didn't want plaster anywhere in my workshop.
*clamps or duct tape
*plastic garden edging 150mm
*new plaster (we used an older bag first, it was yuck)
*reclaim clay
*gloves
*measuring jug
*foam balls from a local emporium. The emporium were a lot cheaper than Spotlight (the other half is now a hump mould). Could use any form though using this method.
*bucket
***I've done it this way because now I have the supplies to make moulds when I want. I've kept everything separate to use for mold making only including a bag of reclaim clay***
ETA: If wanting to making a mould of something that's not round you could also use corflute (try nab an old real estate sign) and duct tape. Just make sure to seal any gaps with clay.
Sample of foam attached to a board (this was my last one which I stupidly didn't cover with clay). If you cover it with clay it will be much easier to release the mold.
Sample of foam attached to a board (this was my last one which I stupidly didn't cover with clay). If you cover it with clay it will be much easier to release the mold.
Sample of biggest foam ball used. I didn't use clamps here, used duct tape instead. Found this a bit easier to handle.
Sample of seal on the outside of the edging.
Mix plaster as per the ratio's on the bag.
I used an old yoghurt container to get the ball and base covered first before pouring in the rest.
Lightly tap the sides to release air bubbles.
Just be careful so nothing moves. I found I needed an extra pair of hands for the bigger mold to hold it while I poured in the plaster but the smaller were fine on my own.
Look no leaks lol
Leave until the plaster is firm, the edging will come away easily once the plaster is firm. I used a needle tool to get out the clay around the rim of the form to help release it. There was a big of wiggling etc before it released but I got all three out eventually.
Sand and wipe down any rough edges.
We found it best to cover the foam ball with reclaim clay. I did one without and ended up with little spiky bits all over the bowl area. These sanded out but can be easily avoided covering the form with clay. I also found it easier to get the foam out.
Sand and wipe down any rough edges.
We found it best to cover the foam ball with reclaim clay. I did one without and ended up with little spiky bits all over the bowl area. These sanded out but can be easily avoided covering the form with clay. I also found it easier to get the foam out.
Leave to dry out for a couple of weeks before using.
I have a bag of clay I use for mold making. Once used you can't use it for anything else because there will be plaster in it and I believe that will explode in the kiln.
I have a bag of clay I use for mold making. Once used you can't use it for anything else because there will be plaster in it and I believe that will explode in the kiln.
Posted: Thursday 11 September 2025