I can still remember the first time that I saw someone use a chisel on stone. I was still in heavy construction at the time, working on bridge decks,expansion joints..stuff like that. Occasionally, the company would have granite curbing that needed to be set on the bridge parapet wall and it was always the same crew. I always want to learn new things, so when the opportunity came for me to work with them I grabbed it. The crew was mostly made up of Peruvians and they had a knack for working with the granite. I watched as a line was traced on the stone with the chisel….up and down, up and down. Then they would slide a 2×4 under the curb and to one side of the line. Next, they would tap the line and then POW! One sharp hit and the stone broke in half, right along the line. This was new to me since the only stonework I had seen done was fieldstone work and no chiseling at all.
It was about a year later that I started apprenticing for a stonemason. I got to use the chisels, learn different techniques and made a lot of rubble while learning. We did mostly granite work and so I had plenty of practice..he even let me take a chisel home and practice.
Before I discuss some basic technique lets look at a few of the more common carbide chisels you would find in a stonemasons tool bag.
From left to right:
Masons chipper – Angled carbide designed to trim, square off or rock face. This is one of my primary chisels.
Heavy Hand Point – For roughing out and knocking off high spots…works similar to a jack hammer with a pointed bit. Four sided carbide with a center point.
Hand Set – This is another trimming chisel but more suitable for flat surfaces. Trim,square or rock face. Square carbide with two edges.
Tracer – For splitting or scoring a line. This is another primary chisel for me. Carbide is ground to a center edge.
Hand chisels – They both have a carbide grind like the Tracer. For roughing out, carving and shaping. I have been using these a lot lately…enough to be considered primary.
Small Hand Point – Same as the Heavy, just smaller.
Carbide Bush Hammer – One side has 36 teeth for fine work the other 16 for roughing out. It has many uses, knocking down high spots, roughing out (gasp) saw cuts, adding texture to smooth surfaces.
Since the focus of this post is splitting, the Tracer is the one we are using.
First you need to examine the stone you want to split or trim. Look for weakness in the stone like fissures or cracks. If you have stone with defined grain structure and it has cracks and fissures running through it, chances are that this stone will end up in the rubble pile if you try to split it. Tracing a line along veins or grain will give you the best chance of success.
Starting your line is next. Light hits are in order now, because you are trying to make a small groove for the carbide on the stone. You do this for two main reasons. One, if the carbide isn’t fully in contact with the stone then you risk breaking it..and these things are not cheap! Second, you want the full force of the heavier hits to transfer along your line, down into the stone. It wont happen if your chisel is bouncing or rocking.
Now that your line is established start hitting with controlled force along your line but ease up when you approach the corner or edge…balancing finesse with force takes practice. Don’t rush. Most bad breaks are because of impatience…trust me on this. There have been many times when I was thinking ” Just SPLIT already!!” swinging away, only to have a bad break ruin the stone. Hold your chisel so that it doesn’t bounce when you strike it. You are sending a “message” into the stone…. a shock wave. Keeping your chisel in contact allows the full transfer of energy to travel into the stone, along your line and hopefully meeting the “messages” you sent from the other sides. If you are not yet bored by this geeking out, read on.
As you are tracing around the stone you will see hair cracking along your line (you hope). If not, all is not lost. If a crack is just starting off your line, just trace your line where it started. It means that the stone is still connected along the line. If the crack wasn’t large to start with, the split will still be successful. Ideally when you trace around a stone, your lines will match up to each other…like sliced bread. Once you get the hang of it or you have been doing it for a long time, this doesn’t become as critical. Look at the stone below..
The line isn’t straight and doesn’t line up. I was splitting along a bedding plane and it didn’t run parallel with the sides of the stone. By going around and around, I was able to make adjustments to compensate and I got what I wanted. Two good stones.
The best thing to do is just have fun with it and practice before you are doing a project were every split counts. Its expensive if you turn good stone to junk and even more painful if you bust a bunch of $100 chisels.
Welcome to Splitsville, population – You!