HardiBacker Board - Gap Behind

[cwhaley]

I'm prepping the fireplace in our front room for a new log burning stove. All of the brickwork/mortar is sound but I want to cover in 12mm concrete board (HardieBacker), as this is what I've been advised to do by the local authorities.

First of all, is this gap necessary? No problem at all if so, but I did wonder why as the original bricks were exposed to a coal fire back when the house was built. Secondly, if it is necessary, does anybody have any tips on how to maintain a gap behind the board? I don't want to use wooden battens (fire risk) - just hoping to hear from any body that has put this board up in this type of application.

 

[Blakes]

Hey there!

I'll soon be doing the same as you once my old inset stove is ripped out!

I had to read your query a few times as it's as if you've missed out a chunk of the story!

Anyhow, it's my understanding the this 'gap' you're talking about refers to the distance between the stove, and the hardiebacker board (distance to non combustibles). As far as I'm aware, you don't need to maintain a gap between the original brickwork and the hardiebacker, just use a heat resistant adhesive and 'dot and dab' the boards on.

Blakes.

 

[John D v2.0]

It's possible they just love spiders, But more likely is the gap is necessary to keep whatever is behind cool. The standards are higher nowadays, back then it was mostly natural selection at work, but now you need to aim for guaranteed safety. The building has likely changed since built and what is on the other side might not be as heat safe as before.

 

[cwhaley]

Blakes - it's certainly a great project to do and so worth it (3 family members have done the same). My query is purely related to HardieBacker so I've left out all of the irrelevant stuff

The gap I'm referring to doesn't involve the stove, no. The gap I mean is the gap between the fireplace brickwork and the board itself. I have been advised by many that dot and dab is not a suitable method for fixing, so I am fixing mine with concrete screws and high-temperature tolerant adhesive. Probably going to tile over the top with full body ceramic tiles.

John D - it would be a great home for them, nice and warm too... I'll go with the gap then; you're the second person to say that today. 12mm boards and 12mm gap, which only means an extra inch either side.

Thank you.

 

[DIYedboy]

If there's another house the other side with a chimney stack, there'll be no need for a gap. When I did mine, I rendered the inside bricks with sand/ cement/ lime (one coat) then painted black, three years later no cracks etc with my Stovax standing in front. If you can get logs free great, otherwise log burners are a waste of time, my log burner cost £1500 and £300 a year on logs PLUS the heating has to go on to heat the rest of the house................£300 a year buys a bloke a lot of gas!!

 

[cwhaley]

If there's another house the other side with a chimney stack, there'll be no need for a gap. When I did mine, I rendered the inside bricks with sand/ cement/ lime (one coat) then painted black, three years later no cracks etc with my Stovax standing in front. If you can get logs free great, otherwise log burners are a waste of time, my log burner cost £1500 and £300 a year on logs PLUS the heating has to go on to heat the rest of the house................£300 a year buys a bloke a lot of gas!!

It is a party wall yes. Despite all of the brickwork being very sound and it being a 60" wide chimney breast, I have decided to leave a 12mm gap just to be sure. Thank you for the input though - good to hear you've had no problems.

I do get a lot of logs free yes (friend runs a treecare company), which was part of the thinking behind getting one. However paying for logs is totally worth it. Maybe it's slightly more in the south, but here I can get a pallet full of seasoned logs for £55-60. If burning 4 a day in the evening, they last a relative of mine for 6-8 weeks. As for the heating, it depends on your property... our neighbours have the same build of house and while they have it on upstairs, downstairs (front room, kitchen, dining room) can be heated just from the burner.

Our stove (Clearview, 2 years' old) cost £450 second hand and it's great. Yes it's an initial cost, but it should last many years into the future.