This is an economical way to get large areas of Rough Slates. 

Prepare the surface using Covent Garden Primer [see Primers and Adhesion Promoters in the Paints Section]. Putting Covent Garden Primer in subsequent paint will promote the paint's adhesion and make it more scratch resistant. Use a flexible paint like Rosco Supersaturated [See Rosco Paints] because these sheets can be rolled up  for transportation. Once the basecoat is dry, the topcoat can be textured and the mortar accentuated by employing texturing materials. Joins can be disguised with muslin. Staple to ply clad flats, see stage braces.