How to make plaster of Paris sturdier

[bullfrog]

Have been trying to knock out several mold sets of small cobblestones to paint and have trouble with the plaster being chalky and breakable. Does anyone know any additives to make it sturdier? I might try a bit of PVA glue both painted onto the final product and mixed into the plaster mix. I wanted to know if there are any other alternatives.

 

[mjs101]

Hirst Arts has some advice. I'd search for key words "hirst arts molds"; towards the bottom of the page is a link to casting instructions, with a section on materials. My casting, personally, has been resins. Best of luck.

www.hirstarts.com/casting/casting.html#material

 

[clarke]

Hi mate,

I've always added a small amount of model hobby glue to the mix and don't have any issues. I only add a two-three drops for a small model stand. Also I've had a similar issue with an old batch of paris, was over 4 years old. Cheers Clarke

 

[bullfrog]

Thanks for the responses. I'll check out the Hirst Arts site. It might be due to the age of the plaster as mentioned because the bag is a few years old by now. Never been opened but still,old.