OK how do you lay a hearth stone?

[Simpo Two]

In a couple of weeks a large slab of pre-cut stone (Hartham Park limestone to be precise) 1300 x 760mm x 40mm will arrive and need to be fitted. The existing ground is the solid concrete floor of the room. The stove is a Stovax Stockton 5 multifuel - so under the grate is an ash pan and there's a 4-5" gap underneath between stove and hearth. Whatever the bed is, it will only need to be 5mm thick.

The local stonemason says use a solid bed to transfer the heat. The local builder says dot and dab. Chesney's website says dot and dab. Somebody else said flexible tile cement.

Who's right?

Edited by Simpo Two on Sunday 13th October 11:23

[Little Lofty]

If only 5mm thick then I'd say a solid bed of tile adhesive, but I don't see why it has to be flexible if not on a timber floor.Having said that I think any of your list would do the job.

[Spudler]

For ease of DIY: dot & dab.
Proper job!: solid.

[B17NNS]

Solid bed of mortar.

[Simpo Two]

Thanks guys. The idea behind 'flexible', which makes sense to me, is to cater for any expansion/contraction as it warms and cools. Then again a solid bed would conduct heat straight into the concrete floor... then again dot and dab would give a cavity for the hot air to esacpe by. I can debate it all ways!

The unknown quantity is how hot/warm it will get under the stove - I suspect not as much as feared due to the large gap beneath, and the fact the firebed is over an ashpan.

[Busterbulldog]

Dot and dabbing it will have the same effect as doing it with tiles...drop something heavy in the wrong place it may crack,hence you always solid base a hearth

[Evoluzione]

Dot and dab every time.

You won't be able to find anything heavy enough to break 40mm of Limestone bridged over a few dabs in a house.

Unless someones going to take a wrecking ball in there and drop it from the floor above....

Heat rises, it won't get very hot. Regardless of this whatever it's bedded on won't make the slightest bit of difference to anything no matter how hot it gets.

Go for a solid bed and you'll be lifting it up and down all day till you get it right.

Mortar will be difficult, but not impossible to get to 5mm, tile adhesive easier, but you'll have to mix it thick and place on large blobs.

[bigdom]

Simpo Two said:

The unknown quantity is how hot/warm it will get under the stove - I suspect not as much as feared due to the large gap beneath, and the fact the firebed is over an ashpan.

Not very. We had this when we installed ours 3yrs ago, so many myths, what 'could' happen, very little based on facts. We went for a granite type of stone (cannot remember what its called), this I laid on a bed of mortar.

The walls were rendered in a 3 to 1 strong mix, sits about 5cms from the back, about 25cm each side. Even running it for days continuously (clear view vision 500), there's never been an occasion where any surface has been at a temperature I couldn't hold my hand against it. Its been on since this morning today, the stone is barely warm.

[Simpo Two]

Sound input, thanks all.

It seems there isn't much to worry about after all, apart from dropping it and breaking it during fitting!

I think, bearing in mind that mortar is not my thing and I note the comments about getting it to 5mm, that I might just buy a small tub of tile adhesive, and use my big 10mm-notched trowel, and treat it like a humungous tile - and just get a strong friend in to help.

If the base is level, and the adhesive is applied evenly, then the hearth will be level too. We'll have to place it an inch or two forwards while we get our hands out, then shove it back to the wall.

Level, thin layer, careful DIY job and no need to call in a builder. Sounds like a plan?

[Spudler]

Butter and notch the underside of slab in opposite direction.

[Evoluzione]

Simpo Two said:

Sound input, thanks all.

It seems there isn't much to worry about after all, apart from dropping it and breaking it during fitting!

I think, bearing in mind that mortar is not my thing and I note the comments about getting it to 5mm, that I might just buy a small tub of tile adhesive, and use my big 10mm-notched trowel, and treat it like a humungous tile - and just get a strong friend in to help.

If the base is level, and the adhesive is applied evenly, then the hearth will be level too. We'll have to place it an inch or two forwards while we get our hands out, then shove it back to the wall.

Level, thin layer, careful DIY job and no need to call in a builder. Sounds like a plan?

• If it's level* then yes I'd go with that.

[Roy E6]

My hearth is an inch thick piece of slate, I just used plenty of gripfill it's not as if it's going anywhere when you have the stove sat on it.

[tonycordon]

We laid our 20mm thick, 'T'-shaped, two piece honed granite hearth on a sold bed of flexible tile adhesive. We had two main considerations, first, to get the level correct and horizontal, and secondly to ensure that both pieces were at the same height. The height issue was because we wanted to fit a sold oak floor on top of 14mm ply (though not under the hearth), on top of the screeded concrete floor, we wanted the oak to appear to disappear under the hearth. We achieved the desired result by carefully measuring the various heights and using spacers of the correct thickness imbedded in the adhesive bed (we used pieces of ceramic tile and thin pieces of aluminium to get the correct height). We then lowered the two pieces of granite onto the adhesive and 'wiggled' them about to get them to sit down onto the spacers. It worked very well and we have had no problems over the last 2.5 years.

[Simpo Two]

Hmm.

So I went into B&Q to buy a tub of tile adhesive, enough for 1m2 whch is all I need.

Except that almost every product in the display was called 'grout', and of the two tubs that were called 'adhesive', both said they could only be used up to 3mm thick.

So do I pile the adhesive up ignoring the instructions, or use grout? At the end of the day the slab is flat, it's not going to move anywhere, it just needs to be properly supported, especially in the middle. If anyone has a link to something appropropriate (not a 20kg bag please!) it would be welcome. Instant grab is no good as it will need to be slid back after placing.

[B17NNS]

I don't think you want grout.

I'm pretty sure Wickes do cement based flexible floor tile adhesive in smaller quantities than 20kg.

Does it really matter what bed thickness you have so long as you have a solid bed all over?

[Simpo Two]

B17NNS said:

Does it really matter what bed thickness you have so long as you have a solid bed all over?

Somewhat yes; it needs to be enough to run a 79 strand speaker cable underneath, but not so high that the fire surround reveals the lintel.

I had hoped to use a thinner slab so I could run the cable in a 10mm copper tube, but they said 40mm was as thin as was safe in that size. Hence there's not much leeway on the bed thickness.

[B17NNS]

Could you not put some packers or shims underneath in the adhesive to stop it compressing further than you want?

http://www.screwfix.com/p/assorted-plastic-shims-1...

[Spudler]

Simpo said:

the two tubs that were called 'adhesive', both said they could only be used up to 3mm thick.

Chuck in a small handful of sand and mix in.
Don't use grout.

[New POD]

When I worked as a fireplace fitters mate, he'd use lines of mortar, with a gap to allow it to extrude a bit.

[bigdom]

This should do the job.


http://www.diy.com/nav/build/building-materials/ag...