Fire bricks are lightweight, heat-resistant clay bricks often used to line fireplaces, furnaces, kilns and other places where fire needs to be contained. Because of the varying shapes and sizes of fireplaces that people use, it is often necessary to resize a fire brick by cutting it. Cutting a fire brick is no easy task, and is generally done with an electric masonry saw, a fire brick handsaw, or chisel and hammer.
Cut the fire brick with a masonry saw and diamond blade for the cleanest, straightest cut. Use a tabletop masonry saw, as opposed to a hand held masonry saw, when cutting large quantities of brick to save yourself time and effort. If you don't want to purchase a masonry saw, you can rent one from a local hardware or home improvement store. Make sure to wear safety goggle and a dusk mask while you saw.
Use a fire brick hand saw if you only need to cut a few bricks. Fire brick hand saws easily cut the brick because they are made with quality nickel and steel that won't be affected or damaged by the rough and tough fire brick grains. Use a mitre box along with the fire brick hand saw to cut the bricks especially straight. Mitre boxes have grooves for helping saw and cut at 90- and 45-degree angles.
To use a chisel and hammer, first draw a line around the brick where you want to make the cut. Then hammer the chisel along the line, scoring the brick at least half an inch deep. Put the brick in a clamp on a table so that the scored area is just past the edge of the table and give the side of the brick hanging over the table a hard whack with a large hammer - ideally a masonry hammer. Use the chisel to break off any leftover jagged pieces of brick.
Do not use wood or metal saws and/or blades on fire bricks. The bricks are highly abrasive and will easily damage your tools. Work with caution and patience when using potentially dangerous tools such as saws and hammers.