Bedding hearth onto suspended floor

[gOBO81]

Hi folks,

 

We are looking to install a balanced flue gas fire, this one in particular. This will be installed into a "false" chimney breast that I will construct and be housed within one of these chambers.

 

The hearth and surround will be Agean Limestone and the issue I have is bedding down the hearth.

 

Our floor is a suspended timber joist floor with 22mm tongue and groove chipboard. The joists run parrallel with the wall the fire will be sited against and there's about 5ft between floor level and the ground underneath. Ideal for running services in under there but not really possible to build up a solid base if there was only a couple of hundred mm under there.

 

As chipboard is far from the best substrate my initial thoughts are to bed down some 6mm HardieBacker boards, cut to the exact size of the hearth, with a cement based flexible tile adhesive before screwing down. I could then bed the hearth onto this with the same adhesive (or sand/cement? not sure which would be best?).

 

I would aim to strengthen the floor prior to starting any work by adding dwangs/noggins under the fireplace to aid minimising movement in that area, and screwing down.

 

Any thoughts or advice on this approach would be greatly appreciated.

 

Rough SkecthUp below minus any additional dwangs.

 

Cheers

 

 

[nod]

A bag of flexi tile adhesive 

Make sure you seal the back of the limestone Two coats 

[TonyT]

Personally I wouldn’t fit one, we had a living flame fire in our lounge 20 years ago and the gas meter spun like mad, it fairly consumed the gas and heat output wasn’t great

 

we ripped it out several years later and installed something else..

 

 

[gOBO81]

11 minutes ago, nod said:

A bag of flexi tile adhesive 

Make sure you seal the back of the limestone Two coats 

Great thanks. Would this be with or without the 6mm HardieBacker?

 

12 minutes ago, TonyT said:

Personally I wouldn’t fit one, we had a living flame fire in our lounge 20 years ago and the gas meter spun like mad, it fairly consumed the gas and heat output wasn’t great

 

we ripped it out several years later and installed something else..

 

 

Appreciate the thought Tony. The room will still have it's CH radiators as the primary heat source. 

[ProDave]

You are over thinking it. The stove only weights 100Kg.  Just lay your chosen tiles or other hearth, e.g a nice bit of stone, onto the floor.

 

Our wood burning stove that is MUCH heavier plus the weight of the flue pipe, sits on a granite hearth just carefully laid on the floor boards and held in place with gravity.

[TonyT]

As did mine, but in the shoulder season when you want some heat and lean towards the feature fire, and then figure out it’s cheaper to heat the whole house.

have fun whatever you decide to go with and good luck with the build!

[nod]

No backer needed 

But as with tiles you need to be careful of anything bleeding through limestone 

Use a tile sealer or SBR Ideally on two separate days If not allow a couple of hours between coats 

[gOBO81]

4 hours ago, ProDave said:

You are over thinking it. The stove only weights 100Kg.  Just lay your chosen tiles or other hearth, e.g a nice bit of stone, onto the floor.

 

Our wood burning stove that is MUCH heavier plus the weight of the flue pipe, sits on a granite hearth just carefully laid on the floor boards and held in place with gravity.

Overthinking....me? My wife would like that comment

 

I think in this instance the hearth we have chosen has upstands on the underside such that there will be hollow areas that will need bedded down the fill the hollows.

4 hours ago, TonyT said:

As did mine, but in the shoulder season when you want some heat and lean towards the feature fire, and then figure out it’s cheaper to heat the whole house.

have fun whatever you decide to go with and good luck with the build!

Thanks Tony. 

 

4 hours ago, nod said:

No backer needed 

But as with tiles you need to be careful of anything bleeding through limestone 

Use a tile sealer or SBR Ideally on two separate days If not allow a couple of hours between coats 

I hear you on the sealer and it was something that was on my radar. I'll go with that then. Cheers!

[gOBO81]

Well, after a long saga having our defective Aga stove replaced due to rust on the door i'm just getting around to making a start on this.

 

Below is a pic of the underside of our boxed and lipped back hearth.

 

I have a bag of Mapei Keraquick flexible addy and I was just wondering how exactly I should bed it down i.e. a full depth and complete bed OR maybe laid in some slightly higher ridges with some troughs between to allow the addy to spread out as the hearth is laid on top.

 

Any pointers before I tackle this tomorrow would be great. I'm just applying 2 or 3 coats of SBR to the back throughout today, giving it time to dry between.

 

 

[Temp]

Ive just installed stone on the walls and floor of a bathroom. I used a trowel with a big notch to get a uniform depth to the adhesive. Eg spread a layer then use the notched trowel to get uniform height ridges. Lay stone and put a spirit level on top. Tap it down and level if necessary.  Clean up any squeeze out around the edges.  

Edited June 18, 2023 by Temp