Granite and honed-slate hearths are perfectly smooth and polished with softened edges. An approximate price for a small to medium-sized hearth is £250 to £400 unfitted. They are reasonable straightforward to fit but are heavy. Shops often offer a fitting service.
Visit a specialist store to find out more about the different materials (there are places that specialise in worktops and hearths).
Sand, cement, PVA.
No. But the dimensions of the hearth will be inspected by Building Control when they inspect the stove installation.
If the stove is to go into a recess it is usual for a granite or honed slate hearth to be in two pieces: the back hearth and the front hearth with a small expansion gap between the two.
When I measure the back hearth I usually make sure it will easily fit in (with approx. 5mm gap at sides and rear). Any gap can always be filled (or if you are lining inside the recess, after fitting the hearth, then the side and rear boards will cover the gap).
If stove is not in a recess then just choose your size and order it.
I always order granite and slate hearths with NO base or upstands – just flat like a counter worktop.
PVA the underside of both pieces and PVA the surface of the floor. Note that there should be NO combustible materials on top of your constructional hearth if you are in a fireplace recess so if a laminate floor impedes into this area cut it back (you can overlap the front and side edges of the front piece of granite/slate hearth onto the laminate (I tend to overlap 1-2cm). Carpet should be rolled completely out of the way at this stage.
Make a sand cement mix (4:1 or similar). It should be wet to medium consistency rather than firm: you want the hearth to end up “hovering” approx. 5mm off the floor, too firm you will not be able to press the hearth down enough onto your mortar to acheive this, too wet and it will compress too much leaving no gap.
It is up to you whether you put the rear hearth down first or the front hearth first. If the floor of the recess is very flat then I would fit the rear first. If the floor is very uneven (sloping or excavated in the recess a little) then the front first. It is the front that is critical (no good fitting the back only to find out that this means the front ends up half an inch off the floor). The problem here is that if you mess up the fitting of the rear peice when you drop it in then it is very difficult to get out again (e.g. if you push it down too much on the mortar and it drops a few mm compared to where it meets the front hearth). I have got this wrong and had to then take the front one up again. The mortar will not have set but it is just frustrating and a little messy.
Put plenty of cow-pat type blobs of mortar on the floor of the recess – about 2-3″ gaps between them at most. Gently lower the hearth onto the blobs. With a spirit level on top of the hearth press it down a little bit at a time untilmit is hovering 5mm of the floor. You may need to press on the hearth and move it around a bit to get the mortar to compress. If your mortar is a little firm you can stand on the hearth. If you cannot get it down enough then you have to choose to leave it a little high or take it up and start again with a wetter mix.
Allow to set overnight. Voila!