Cutting your own firebrick (or any other square brick or stone) is no big deal - all you need is a hammer and chisel. You could use power tools, I suppose, but if you’re only cutting a few bricks for one project, it’s faster and cheaper to use hand tools. I take great pleasure from learning that I can do easily something I thought was really tough or complicated, and many folks these days are unfamiliar with, and intimidated by, simple tools and rough materials:
“But you have to be an expert in order to cut stone,” you think. “What if I get it wrong?”
Well, if you get it wrong and can’t fix it (OH NO!), then you must:
- Locate and acquire another rock or brick. (I understand these are cheap
and widely available)
- Look at your broken brick and spend a moment thinking about WHY it didn’t work. Then decide what to do differently, feel good about it, and try again.
- Repeat if necessary. I learn something most every time I mess up. I figure that’s worth two minutes of observation and a brick, but you can do the math yourself and decide.
Pieces and Parts
You can improvise with almost any heavy chisel and whatever hammer you like or can find. I have used a cold chisel (a heavy, dull chisel for cutting cold metal) as a substitute in the past with some success, but masonry chisels are usually available at your local tool store for cheap, and trust me, that wide blade (see photo) makes your job much easier. I use a 2 lb. short sledge, and a masonry chisel I bought at a hardware store for $5. Wearing long sleeves and gloves ($4) can help protect you from flying chips, and eye protection (also $4) is essential. I like working outdoors, but you can do this in any well-ventilated area. If you decide to improvise rather than buy a masonry chisel, try not to use the fine-edged chisels that are made for cutting wood or hot metal; cutting brick or stone will tear them up.
Some people prefer to lay the brick on packed earth or sand when scoring, as they believe that it helps hold the brick fast, and transfer momentum from the chisel through the brick more efficiently. I have used a bare wooden workbench or a pile of other bricks in the past without incident. In the photos, I’m using my porch. I should note, though, that the height of your work surface makes a big difference. If you can put the top of the chisel at the height of your hip or so, your hammer will be at a much more comfortable angle for repeated swinging. Experiment and find what works for you.
Measuring and Marking
Before cutting, lay the brick flat on a workbench, measure where you would like to cut, and mark this with chalk or a pencil if you want. To break the brick, we’re going to use the chisel to score it; this will create a controlled, precise crack all the way around the brick, so that the break happens right where we want. If I want a perfectly square break, I generally mark lines, so that I don’t make a chisel placement mistake.
To score, set the chisel against the brick on the marked line and wrap your hand firmly around the straight part of the chisel, keeping your fingers and thumb between the striking surface (‘hammer’ + ‘fingers’ = ‘bad’), and where the chisel starts forming the blade. Hold the chisel upright and steady but don’t squeeze - squeezing will transmit the shock of the hammer blows to your hand and can tire or injure your hand; I find that wearing gloves really helps with this, because your skin doesn’t stick to the chisel. If you’ve never done this before, lightly tap the top of the chisel with the hammer a couple of times, holding the hammer so that the head is a couple of inches above the chisel, and then dropping it. This will give you a feel for what’s going on. Repeat this if necessary until there is a visible mark on the brick.
Smooth and Steady
Try not to cut one spot too deeply all at once; this can cause the brick to break in ways that you don’t want; cut each side about the same. Once the brick is lightly scored all the way around, go around again, striking a little harder. If you haven’t ever used a hammer or chisel before, this is where you can experiment – each time you go around the cut line, hold the hammer a little further up in its arc before letting it fall. Try to get comfortable with how the hammer wants to fall gradually - it may seem tedious, but it will give you much better aim later when you want to swing full blows.
The Right Way to Do Things (cleanly cut bricks, happy hands, and peace on Earth)
The Wrong Way to Do Things (Crooked cuts, flat fingers, and the sound of the Doom Bell)
When breaking stone, the most important thing is to confidently follow through with your hammer. That doesn’t mean that you need to swing hard, but you need to let the hammer transfer all of its momentum to the chisel, and the more relaxed you are when you do this, the more likely you are to strike straight and true, and thus get a straight crack. In my experience, a little confidence helps you relax, and practice gives you confidence, so go hit some rocks (safely). Below, the ragged horizontal break is what happens sometimes if you don't score all the way around (I just pounded the chisel through the top of the brick, and this is what the bottom looks like) and the clean vertical break (with white scoring marks) is what happens when you score evenly; you get a nice, straight break.
If the brick doesn’t immediately break (firebrick usually takes a couple more hammer blows than regular red brick; I think this is because it is made of smaller aggregate, and baked hotter) just put the chisel back in the score line and start digging it deeper, being more aggressive with your hammer blows. It’s important here to keep the chisel straight upright, and to swing your hammer with good control so that it comes down straight onto the chisel; an angled chisel can cause a crooked break.
Cutting stone is not rocket science. The most important thing is to try it, and to not worry. It might go wrong, but I guarantee you that if it does, you’ll be able to figure out why and fix it, and you’ll feel good for having jumped out there and learned a new skill.