Cutting slate

[Kit Jackson]

I've got a new slate hearth for the fire. It's 20mm thick but unfortunately it's a bit too big and I'm planning to use a stone cutting blade on an angle grinder to cut it to fit. The slate will sit recessed inside an existing marble surround so the edges don't have to be particularly smooth but they do have to be straight.

First question - should slate be cut wet or dry? Do I have to provide a stream of water directed at the point of contact. Next - are ordinary angle grinder blades OK to use wet or will the blade disintegrate. Would I be better using a diamond blade instead? Finally - does anyone have any tips for keeping the cut dead straight?

Kit Jackson

[Andy Burns]

I cut a slate hearth down in size with a segmented diamond blade, didn't wet it, cut was OK, similar to yours my edges weren't on display.

[newshound]

Not slate, but I had no problem cutting up sandstone paving dry using a diamond disk in a 9 inch angle grinder last year. I also did some nibbling with a 115 mm blade. You would probably be OK using this size if you take it slowly.

Don't try to make it too close a fit in the first cut, it's difficult to take small amounts off neatly if it is too tight. The opposite to the usual rule for timber products!

[tabbypurr]

Upto you. Wet is better.

Never wet grit discs, it can cause them to fail. And angle grinder disc explosions are really not a good thing.

oh yes. Faster neater cleaner quicker safer, and over time cheaper.

I doubt you will without some equipment designed to.

NT

[John Rumm]

It will cut dry with a diamond disc. (slate is not particularly hard anyway). (with skill it can also be worked with hand shearing tools, but I don't think I would try that without lots of practice!)

Stick to diamond. Most masonry cutting tasks are far easier, faster and cleaner with a diamond disc. The continuous rim discs like some of the Norton ones will also give a very smooth polished cut.

Use a timber batten clamped onto the work to run the side of the blade along.

[Dave Plowman (News)]

Don't suppose you have a wet tile cutter? Larger ones will cope with 20mm. If the edge is already square, the fence on that will keep the new one square too. A wet cut with a diamond blade done carefully will give a superb cut.

[tabbypurr]

With a diyed sled you could get a good cut. Without I can't imagine holding a big heavy piece of slate steady enough all the way through to get a clean cut.

NT

[The Natural Philosopher]

dimond,water, dunno/

[Dave Plowman (News)]

You'd need to make sure the tile cutter was fixed down to something and have skilled help to move the slab. But if you are skilled with an angle grinder you could probably do it with that. I'm not.

Other way might be to fit a diamond blade to a circular saw?

[tabbypurr]

then run it along a batten.

NT

[Jonathan]

Jonathan

[Huge]

[15 lines snipped]

[Files that away as useful, since I have vague plans to make a turntable plinth out of slate.]

[Dave Plowman (News)]

Then I really would use a wet tile cutter. As I said you get a beautiful edge with those. I cut some concrete paving with one - slow, but I'm not happy with angle grinders. The edge looked wonderful with all the cut and polished aggregate. Even although it would never be seen again. ;-)

[Dave Liquorice]

Do it outside, slurry spray if done wet, dust if done dry...

Diamond blade, perhaps hire a decent sized machine. Even then I don't think I'd attempt a hand held, single pass, full thickness, cut.

A batten very firmly clamped to the slate to guide some rigid part of the body of the machine, not the blade directly, should give the straightness for the exposed corner. This cut done fairly shallow, slowly and carefully then turn over and do multple passes from the back to cut through the thickness, guide batten to start. The two cuts don't have to be exactly opposite each other, I'd probably go for the kerf larger for the cuts from the back.

[John #9]

I've found that having a dust extractor guard fitted to the grinder makes that sort of thing much easier:

[John Rumm]

That looks quite handy - half way to being a wall chaser.

[DICEGEORGE]

Bosch PMF (or £20 clone from aldi this week)

[Kit Jackson]

Job done last weekend. I'd just like to say thanks to everybody who replied.

In the end I used a stone grinding wheel to produce a scoring cut on the face, then the main cut using a diamond wheel on the reverse. The grinding wheel produced a better edge than the diamond wheel where I got some breakout on the cutting side, maybe because I used a segmented blade which just kicked the lip of the cut off a bit. Or maybe because I'm not very good at using the angle grinder. I did run the blade up against a piece of small angle iron to help keep a straight line as well. All the cuts were done wet.