When I was preparing a display base for an Airfix 1/24 scale Harrier, I discovered Liquitex Coarse Texture Gel. It can be mixed with any acrylic paint; I used two shades of brown Apple Barrel craft paint. I roughly mixed the three ingredients together to represent well-trodden mud.

I pushed the PSP matting into it while it was still wet, and easily cleaned up the ensuing mess around the edges with a kitchen sponge. (Don’t tell the wife!)

Liquitex also makes a smooth version I think would be great for watery dioramas.

Tip submitted by:
Richard EllisJonesborough, Tennessee