Special cement is used to make refractory bricks. You can buy refractory cement at your local hardware store or you can make it from scratch. Making your own refractory cement requires masonry cement in the mixture, which is different than Portland cement. Portland cement will explode in high heat, whereas masonry cement tolerates high temperatures. Building your own mould for the refractory brick will take a little carpentry skill and a few tools. If you do not have the tools to make the mould, you can rent them from your local tool rental store.
Cut the 2-inch by 4-inch studs. Cut them to the length and width needed for the size brick you are making. For example, for a brick slab measuring 24 inches by 24 inches, cut two studs of 24 inches and two studs of 27 inches. Screw each end of the 27-inch studs to the butt end of the 24-inch studs, creating a 24-inch by 24-inch box or square.
Lay the box on a flat surface, such as the floor or table. Cut a piece of plywood to the measurements of the stud box. Screw the plywood to the box, every 5 inches. Flip the box over so the plywood is on the smooth surface.
Caulk the seams where the plywood meets the studs and each corner where the studs meet. Rub vegetable shortening all over the inside of the box, including the plywood bottom. Or, use polyurethane to seal the wood. Lay the box on another piece of plywood, but do not fasten down the second piece of plywood.
Mix the refractory cement. Lay a piece of plastic sheeting on a smooth surface or you can mix the refractory cement on a smooth, concrete surface. Pour out one and a half parts masonry cement, one and a half parts perlite, two parts fireclay and two parts sand. Stir the dry mixture using a shovel until it is thoroughly mixed.
Create a hole in the centre of the dry mixture. Pour a half part water into the centre of the hole and slowly fold the dry mixture into the water until the mixture is crumbly. To test if the mixture is the right consistency, make a ball out of the mixture and toss it up in the air. If the mixture stays together when you catch it, then it is the right consistency. Add more water until the mixture is at the right consistency.
Fill the mould with the homemade refractory cement. Pack the cement as much as possible. Slide a 2-inch by 4-inch stud across the top, back and forth, to smooth out the cement. Make it even with the top of the box. Vibrate the second piece of plywood, using a hammer drill and a scrap piece of wood. The vibration will settle the cement and remove any air bubbles. Continue until the top of the mould is smooth and all of the air bubbles are gone.
Cover the cement in the mould with a piece of plastic sheeting. Tape the plastic to the outside of the mould using duct tape. Keep the cement moist for a couple of days, then remove the plastic and let the cement cure for an additional two days.
Release the brick. Remove the screws from the plywood and the ends of the studs to remove the mould from the refractory brick.