Fitting a new fireplace surround

I'm about to fit a new limestone fireplace surround, the centre part where the hearth is to be placed was already concreted but the hearth is too long and the edges rest on the wooden floorboards.

The hearth has sections underneath that make contact with the floor as seen in the second picture, the middle two supports would rest on the solid concrete, the outer two would be on the floorboards.

Do I need to concrete the whole area underneath where the hearth sits, or could I use some other sort of adhesive to make the base strong enough to avoid cracking should someone stand on it?

I'll only be putting an electric fireplace in there.

Thanks.

The hearthstone looks to have been designed such that only the supports are intended to be grounded, so as long as they are on firm/level footings (of whatever material) you should be good. Perhaps you could lay some timber of an appropriate thickness between the supports to be safe. Depending on its weight you may not need much adhesive. Concrete would be a bit permanent, and difficult if done wrong or you ever fancy a change!
Presumably the stone has a facing on the other side.

does the fire surround sit on the hearth? if its limestone im guessing its pretty heavy, (last one i did weighed a ton)
in which case you do need a firm base, if the floorboards are pretty solid they should be ok but make sure all 4 supports are in contact with the ground, use packers underneath as required.

Halitosis said:

The hearthstone looks to have been designed such that only the supports are intended to be grounded, so as long as they are on firm/level footings (of whatever material) you should be good. Perhaps you could lay some timber of an appropriate thickness between the supports to be safe. Depending on its weight you may not need much adhesive. Concrete would be a bit permanent, and difficult if done wrong or you ever fancy a change!
Presumably the stone has a facing on the other side.

Click to expand...

Thanks for the reply, I'll lay some timber underneath between the supports, I'll make sure the floorboards are nailed down tightly too so that there's no movement. Do you reckon standard builders adhesive will be sufficient?

Yes the stone has facing at the front, so anything I put underneath will be out of sight.

kazuya said:

does the fire surround sit on the hearth? if its limestone im guessing its pretty heavy, (last one i did weighed a ton)
in which case you do need a firm base, if the floorboards are pretty solid they should be ok but make sure all 4 supports are in contact with the ground, use packers underneath as required.

Click to expand...

Yep, the surround sits on the hearth and it is bloomin' heavy. I've got a bag of assorted packers, so I'll make sure it's nice and level and supported. Thanks.