Things You'll Need
Concrete or clay bricks for models
Wood or plastic box large enough to hold several bricks
Acrylic spray sealer
2-part pourable urethane rubber compound
Clean mixing bucket
You can use the mold box over and over again to make as many brick molds as you like. Cast concrete bricks take several days to fully cure, so the more molds you have the more bricks you can cast and cure at one time. Be sure your brick models are the correct dimensions for your application. For instance, veneer bricks may be less than 1/2 inch thick, whereas driveway paving bricks should be about 2 1/2 inches thick. You can give your brick project a vintage look by molding weathered bricks or even stone blocks.
Pourable urethanes emit toxic fumes as they cure. Be sure to do your mold-making in an area with good ventilation. Failure to seal and use mold release on the bricks and molding box may make it impossible to remove the cured urethane mold without damaging it.
Casting your own paving or veneer bricks from concrete can save you money, but commercial molds are expensive. Making your own brick molds is easy and a lot cheaper. Since it allows you to make lots of molds, you can cast more bricks at once, which can cut weeks or months off your project time.
Seal the inside of the box with acrylic spray sealer if it is made of wood or other porous material. Allow the sealer to dry thoroughly.
Arrange the bricks in the bottom of the box. They should be an inch away from each other and an inch away from the sides of the box.
Spray the exposed surfaces of the bricks with acrylic sealer and allow it to dry thoroughly. Then paint the exposed brick surfaces and the exposed inner surfaces of the box with liquid mold release, using a paintbrush.
Mix the two-part pourable urethane in a clean bucket according to the manufacturer's directions. Then pour the urethane over the bricks, up to one-quarter of the way under the upper edge of the box.
Allow the urethane to cure to full strength; this usually takes between one and four days.
Invert the box to release the urethane mold. Pull the bricks from the mold. Clean away any brick dust that may be clinging to the mold.
Scott Knickelbine began writing professionally in 1977. He is the author of 34 books and his work has appeared in hundreds of publications, including "The New York Times," "The Milwaukee Sentinel," "Architecture" and "Video Times." He has written in the fields of education, health, electronics, architecture and construction. Knickelbine received a Bachelor of Arts cum laude in journalism from the University of Minnesota.