Splitting Large Stones

When we bought our current house it came with the mother of all rockeries. I kid you not this thing was built to survive a direct nuclear hit. The largest stone probably weighed in at 150kg and perhaps more than that. It took both the wife and myself to shift it a couple of meters across the garden and that was after I’d built a sled to make it easier to move – it only went a couple of meters because it crushed the sled which was made out of 2×4.

The rocks sat in a large pile in the garden for about 18 months while we did other things but I decided the other day that it was about time we got rid of them. Due to the difficulty we would have moving them we had toyed with the idea of just making another rockery but that felt defeatist to it was time to break them up.

The type of rock makes a big difference, fairly even grained rocks seem to break easily and cleanly. I was mostly dealing with an oolitic limestone (Cotswold stone I think) which has a sort of intertwined grain running through it which makes it much harder to split.

You might think that breaking rocks is fairly easy but let me tell you it’s bloomin’ hard work and you’ll discover there’s a good reason they made prisoners break rocks as a punishment. Smaller rocks, up to about what an average (modern) man can lift are fairly easily dealt with using just a sledge hammer. Rest them on something hard with one end propped up and whack them a few times and you should find they split.

Unlike the smaller stones the larger stones require a little brain power as well as muscle power. Rather than just trying to better your way through the stone which will never work get out your trusty SDS drill (you do have an SDS drill don’t you?) and drill three 12mm holes about 150mm deep. Drill the first hole roughly in the centre of one face of the stone than drill two more about 50mm either side in a straight line. Why three holes? I tried with a single hole and some stones split and some didn’t. I then tried with numerous holes, also known as chain drilling, and it didn’t make the job significantly easier. With three holes I found I got a good clean split for the minimum of effort.


Once you have your three holes drilled get out your chisel. Mines about 40mm diameter and 350mm long and perfect for this job. You need something big and strong as your going to be giving is a really walloping. You want your chisel to be about twice the diameter of your pilot holes. This allows your chisel to get started but also means it can split the stone.

Place the chisel in the middle pilot hole and hammer on the end until it’s seated in the stone. use a 2.5kg lump hammer or something like that. Once the chisel is in the hole you can hit with with whatever you like. I’d normally use a 3kg sledge hammer but mines broken so I used an old 5kg lump hammer I found. If you use a lump hammer be careful of missing the chisel and catching your fingers – you won’t get a chance to do it twice!

With any luck after a bit of hammering you should have a cleanly split stone like the one shown here. I got lucky with this stone and it split into three pieces.