Firebrick Mold

Warning! This uses high voltages and high temperatures and can be very dangerous. You make and use at your own risk!

Homemade firebrick recipe:
4 parts Pearlite
2 parts Type S Mortar
1.25 parts Water
I used a yellow plastic cup to measure and it this recipe makes one brick 13cm x 6 cm x 26 cm.

Why S Type mortar? Because it has cement and sand already in it (you don't have to buy each separately) and it only cost me about $6 for a 60lb bag of it. I bought two of the small $5 bags of Pearlite from Lowes. So 8 firebricks cost about $16 and there's over half the bag of Type S Mortar left over.

Let the bricks dry for over a week. Yes, a week. The bricks will be fragile. You can flatten them by rubbing them on your driveway or sidewalk to remove high points. You can cut the brick with a sawsall or sheetrock saw (for mitering). Then you'll want to warm the brick to about 180F (90C) for an hour or two to expel any remaining water before getting it any hotter or steam could b