Start with wood- or steel-framed flats, covered in 1/4" lauan. Muslin-covered flats will work for the Sculpt-or-Coat and sawdust methods, but you will have better (and more 'solid') results with a 'hard-covered' flat surface.
For methods where you will use masking tape to create the mortar lines, prime your flats the mortar color and spatter with a highlight and a shadow before applying the tape.
After applying tape for the mortar lines, spread Sculpt-or- Coat over full surface. Use sponge to daub at the surface to create desired texture. Pull up tape before the surface dries. Let the surface dry and then paint.
What a cost effective and easy way to do bricks! Cut out desired sizes of brick and glue to the surface with white glue or Sculpt or Coat. Add a light layer of Sculpt or Coat to top surface of bricks to help seal and add an additional texture. Daub with sponge or rag to give surface texture while Sculpt or Coat is wet. Let Sculpt or Coat dry and then paint.
Scene shops often have a sawdust collection system or you may have piles of sawdust around. Save this stuff and recycle it! If you don't have a collection system, keep a clean garbage can with mesh over the top to sift out the larger pieces. Then you will have all the sawdust you need.
After applying tape for the mortar lines, brush full strength white glue over area. Shake sawdust generously over the surface. Pat down sawdust with gloved hands. Elevate and tap surface so the excess sawdust falls off. Remove all masking tape before the bricks dry. Let bricks dry completely before painting.
Drywall Mud Method
After applying tape for the mortar lines, apply drywall mud with a spatula or putty knife, spread thinly over the surface. Use a natural sponge and daub at each brick area to give texture. Adding white glue, Phlexglu, or Sculpt-or-Coat to the drywall mud (about 1 part glue to 9 parts mud) gives the mud a little flexibility and better adherence to the flat.
After the desired texture is accomplished, pull masking tape up while mud is still wet. Let mud completely dry before painting. Remember that when drywall mud is painted the first time, it tends to "tint up". (When the paint dries, the paint will be lighter in hue than the original paint color.)
Foam and Router Method
Use this method for mass production...when you have a lot of square footage to cover.
This method is subtractive, in other words, you will be removing the mortar lines from a 1/2" thick, 4' x 8' sheet of white foam, sound board, or blue foam. Use a 1/2" straight bit to cut your mortar lines. Determine the size of your bricks, using a size that will divide evenly into a 4' x 8' sheet.
Build two different jigs for your router... one for the horizontal mortar lines and one for the vertical. Make the horizontal cuts first, then the vertical passes. Prime the foam with Rosco Foam Coat, Rosco Tough Prime, or Sculpt-or-Coat before painting.
Bricks and Stones to walk on
If you want a brick or stone surface that will take the wear and tear of walking, the Sculpt-or-Coat or sawdust methods will work.
Possibly the best way to get a realistic stone texture that will stand up to abuse is to use 1/2" Homosote (sound board). You can cut the board into stone or brick shapes, then split it into two layers. The raw side exposed by the split has a great texture that reads well onstage and provides some traction for the actors. If you want a smoother stone surface, use the Homosote 'as is' without splitting. Glue the pieces down, then seal with Sculpt-or-Coat or Phlexglu and paint.
For all floor surfaces, you will want to take extra care in sealing the paint, using a flexible sealer such as Plastic Varnish (gloss or flat, depending on the look you want).
After Textures are Dry, Use These Painting Tools
Lay-in Brush: great for laying in mortar color.
Spatter Brush: good for adding visual texture to bricks and mortar.
Natural Sponges: nice for adding visual texture, high and lowlights.
Chalk or Charcoal: useful for adding graffiti and for layout.
Small Lining Brush: helpful for shadow washes and highlights.
Spray or Mist Gun: super for adding visual texture.
Stencil: quick material for mass production.
Paint Roller: fast way to cover large areas.