Hi folks 

I need to cut down a 20mm thick slate hearth. One cut edge will be against a wall at the back once installed,  but a cut along a side will be visible so needs to be pretty god.

How best to make a nice neat square cut? Can a suitable disc be fitted a circular saw?

Thanks 

clamp timber to it to use as a guide for the blade, cut slow and plenty of water.

OK. Do you mean with an angle grinder or circular saw?

would have thought a 9 inch grinder and new diamond blade would make short work if it. You can buy a bull nose wheel for the grinder as well to soften and smooth the edges after. The lads who did our hearth had one made a lovely job of it.

Cut with an angle grinder. Ebay will get you a set of diamond polishing pads for a small angle grinder. Go down using the grades and you will get a perfect finish. I have a set that i have used a few times on granite for window cills etc. A perfect polished finished to a meter long cut takes about 10 mins.