Cutting sandstone paving with angle grinder

[treppan]

Hello fellow DIYers.

I'm about to replace a sandstone paving slab that broke recently (thanks to a shoddy installation job from a cowboy builder), the dot-dab mortar crumbled away underneath (extremely sandy mix) and gave way when a car parked with a wheel on it.

I've got a replacement sandstone paver, but it needs cutting down to size. The 600mm width is fine, but I need a straight cut to reduce it to ~400mm in length.

Yesterday I purchased an angle grinder and diamond cutting wheel, and I've already got goggles/gloves/disposable dust mask.

I want to make sure I do this safely, so how would you suggest I go about cutting this? I've never used an angle grinder before.

I was going to mark up the cut with a pencil, place the flag on a bag of sand with the cut hanging over the end. Clamp a wood guide along the line of cut, then use this to score a few mm in with the angle grinder. Once that's done, remove the clamps and keep cutting till about half depth, then hammer the rest off from behind.

Does that sound right? Are there any safety concerns I should be aware of when using an angle grinder? I imagine these can cause some nasty injuries if used incorrectly, so I want to make sure I do it safely.

 

[JohnKay]

Hi treppan

You are very wise to ask. I assume this is a 9 inch grinder. Firstly make sure the disk is installed the right way round, the direction of rotation is marked. Fit the side handle so that when cutting the rotation would pull the machine forward, and the dust towards the rear.
Place the slab on a board, a flat layer of sand, or even straight on grass, not a bag of sand.
Forget the wood guide, good in principle, but could cause problems as the disc rubs on the wood, may even kick back.
Simply mark the slab, you may have to score the surface in order to see the mark. pencil has a habit of disappearing in front of a grinder !
Cut freehand, a very light cut along the line, then another pass to deepen, and then straight through. No hammering off needed.

The important thing is to keep control, make sure the disk is at 90 degrees to the slab, and try not to deviate from the line.
It would be a good idea to get the feel of the thing before the serious work. Not something to be frightened of, but the power of a grinder, together with the gyroscope effect may take a bit of getting used to.

 

[treppan]

Thank you John, I value your advice.

It's a smaller 115mm angle grinder (4,5"), as I thought that would give a deep enough cut and easier to handle as a first go.

I'll stick the slab on the grass and avoid the wood guide... I'm glad I asked about that, as I never thought about it rubbing and causing problems. I should have enough spare space on the slab to make a couple of small test cuts to gauge how it works.

If it does kick back, is it likely to go flying - or am I just overestimating the power? I've seen someone with a nasty injury from one of these, so I've always been hesitant to use one.

 

[JohnKay]

You could cut from both sides. As long as you hold it firmly, and not let the disc bind in the cut, all will be fine.

 

[treppan]

You could cut from both sides. As long as you hold it firmly, and not let the disc bind in the cut, all will be fine.

Thanks, I'll do just that. I'm off to buy the rest of the tools I need and then get started.