Build a brick wall against chimney stack

[Lars-Göran Lindström]

Hello

We have a chimney breast that exposes aerated concrete towards the outside. We are planning to brick it with bricks recycled from a demolished cottage that stood on the property.

It is specified that there should be a 5 cm air gap closest to the aerated concrete.

I wonder:
- how do I build the air gap? Material choice, etc.?
- how do I attach the brick to, as I assume, the "panel" for the air gap?
- calculate the amount of cement required for a brick wall that is 140x400 cm
- what else should I consider

 

[Claes Sörmland]

Is that air gap to cool your chimney flue in aerated concrete, your "murstock"? If so, it must be open at the bottom and top for the air to circulate.

Otherwise, I don't see any need for any sheet material. You build your brick wall in front of the murstock with a 5 cm gap. At regular intervals, you position a brick so that the header side of the brick is supported against the murstock, meaning a header brick in the masonry.

 

[Lars-Göran Lindström]

The air gap, is it to cool your smoke channel in lightweight concrete, your "chimney"? If so, it must be open at the bottom and top for the air to circulate.

Otherwise, I don't see any need for any sheet material. You build your brick wall in front of the chimney with a 5 cm gap. At regular intervals, you place a brick so that the head side of the brick is supported against the chimney, essentially a header in the masonry.

Yes, it is prescribed to be open at the top/bottom.
Cooling? Not really sure

How do you prevent the brick wall from falling outward?

 

[Claes Sörmland]

Yes, it is prescribed to be open at the top/bottom.
Cooling? Actually, I don't know

Then it's about cooling. So that the smoke channel doesn't overheat. You should leave gaps in the brick at the bottom and top.

How do you prevent the brick wall from falling outward?

Tie it to the back wall. Is it possible to screw, for example, steel studs into the "chimney breast," meaning the part where there is no flue behind? Then you can tie the wall from these steel studs.

 

[Lars-Göran Lindström]

Then it's about cooling. To ensure the flue does not overheat. You should leave gaps in the brick at the bottom and top.

I use the term chimney for lack of a better word. The house is built of light concrete.
Inside my so-called chimney, there's a corresponding chimney with a built-in Jøtul stove. The construction is made of some fire-resistant material and clad in the same brick that we want on the outside. The stove has a steel pipe that leads out through the roof. The pipe is free-standing and the "chimney" there is ventilated.

So we have a stove construction of fire-resistant material + brick facing the room and light concrete on the outside.

 

[Lars-Göran Lindström]

I checked with the constructor.
He admitted that as the construction developed and with the chosen stove solution, an air gap is not needed. A relief for me.

However, he wanted to leave air holes in the brick wall. These are made by omitting mortar between the bricks (short side) at regular intervals. (Will be able to see the lightweight concrete behind).

The suggested interval was 0.5 m horizontally and 1 m vertically.

Now it's about finding wall ties that work on lightweight concrete.

 

[RassellCrow]

Leaving that 5 cm air gap has worked well for me before, and I just tied the new brick skin into the sides with metal wall ties so the whole thing stayed put without stressing the aerated concrete. I also kept the reclaimed bricks damp so they didn’t suck the mortar dry too fast. I once had Emerson Chimney & fireplace New Jersey https://emersonproservices.com/new-jersey/chimney-fireplace/ check a similar setup, and their tips on ventilation clearance kept things trouble free.