Casting plaster rocks on a steep surface

[Bob]

I will shortly try my first large scale attempt at casting plaster rocks on to a styrofoam base.  The slope will be steep, so my question is whether the plaster will adhere sufficiently well, or should I put screws or nails into the styrofoam slope with the heads sticking out some to give the plaster something else to grab hold of?  I will eventually cast rocks to make Maryland Heights (see first page of my Cumberland Subdivision thread) and this will be both steep and large, and I don't want landslides to occur!  Anyone have experience with this?  Thanks!  Bob

[wvgca]

best off letting the plaster get 3/4 hard, so that it will still somewhat conform to the surface .. i used this method on my layout eight years ago, and so far it's great

[Scottl]

I purposely leave the styrofoam surface rough to help adhesion.  Nails or screws would work too but might be awkward with some molds.

[CRL]

Do what the stucco guys do. Apply a scratch coat to the surface.

[MetroRedLine]

Cast them outside the layout, then use adhesive caulk to glue them to your styrofoam scenery base. Use sculptamold to fill in any cracks/gaps. Paint everything over with a coating of artist's gesso, then stain/paint as desired.