What materials should we use for DIY diorama bases?

[JamesXGZ]

Hi guys, this is something I've always wanted to do, but couldn't find any resources or articles.

What I have in mind was to do some DIY rocky diorama base like (refer to attached) for my one sixth figures.
I have tried using Plaster of Paris with a matte spray sealant across it but the surface is still too 'powdery' for me to display my characters on.

Is Plaster of Paris the correct material for diorama use?
Or is there any paint/ finishing products that helps 'seal' the plaster cast within?

Thank you.

Attached image:

 

[K.bowen]

my brother makes dioramas for 1/18 figures and he just uses big blocks of Styrofoam(cant spell) he made me a stone base for a figure and it turned out great, obviously its time consuming I think he cut the shape roughly then used some sort of tool to add rock texture then coated it in watered down pva glue, I think many home made dioramas for minatures also do the same thing, there would probably be tutorials on the net somewhere

 

[JamesXGZ]

my brother makes dioramas for 1/18 figures and he just uses big blocks of Styrofoam(cant spell) he made me a stone base for a figure and it turned out great, obviously its time consuming I think he cut the shape roughly then used some sort of tool to add rock texture then coated it in watered down pva glue, I think many home made dioramas for minatures also do the same thing, there would probably be tutorials on the net somewhere

Thanks Bowen, I'll experiment with styrofoam. Anymore materials up for suggestions?