ᐅ Exterior walls made of aerated concrete and interior walls constructed from brick?

Hello everyone,

Recently, we signed our house construction contract. Originally, the exterior walls were planned to be brick with external thermal insulation composite system (ETICS).
Instead, we chose aerated concrete (with an additional cost).

The material for the interior walls remained as stated in the contract (brick). We overlooked this. There was also no advice from the builder suggesting that using the same material for both interior and exterior walls would be recommended.

If we keep it this way: is there a risk of cracking? Does this kind of "mixed masonry" meet current technical standards? Is there any relevant DIN standard or just common sense that speaks against it?

According to the contract, we will receive a house built according to the state of the art. Preventing possible cracks using mesh tape (applied in the corners) should not be a solution, right?

What do you think?

Thank you in advance!

Hi
wait about a year or so, then I can report back.
We will have aerated concrete on the outside and calcium silicate bricks on the inside. It’s part of a program for barrier-free living, designed to ensure that reliable support points for grab handles or rail systems and similar aids are available later in life or in case of disability. Regarding cracks, we were told that the interior plaster can generally develop microcracks, for example, around window reveals. We originally planned to paint directly onto the plaster, but were advised against it because of these microcracks. Nothing was mentioned about cracking due to the different types of masonry. Since indoor temperatures vary only slightly throughout the year, I don’t expect significant risk there. We will have a fiber fleece applied and then paint over it, which will mask the microcracks. The same applies to the drywall ceilings.

Aerated concrete more expensive than brick masonry with external thermal insulation composite system (ETICS)? That's new to me. And reinforcing mesh applied in corners is supposed to prevent cracks. Well!? Are the interior walls built in bond with the exterior walls?

ennos2 schrieb:
Hello everyone,

We recently signed our house construction contract. Originally, brick and external thermal insulation composite system (ETICS) were planned for the exterior walls.
Instead, we decided to go with aerated concrete (additional cost).

According to the contract, the material for the interior walls remains the same (brick). We overlooked this. There was also no advice from the builder that using the same material for both interior and exterior walls would be recommended.

If we leave it as is: is there a risk of cracking? Does this kind of "mixed masonry" comply with current building standards? Is there any relevant regulation (e.g., DIN) or just common sense that argues against this?

According to the contract, we are to receive a house built according to the state of the art. Preventing possible cracking with mesh (applied in the corners) shouldn’t be the solution, right?

What do you think?

Thanks in advance!

Don’t worry, this is quite common since sand-lime bricks have more mass and therefore provide better sound insulation, which is only beneficial for interior walls. Also, the thermal insulation advantage of aerated concrete between interior spaces is usually irrelevant, whether we are talking about an aerated concrete, timber frame, or Poroton exterior wall.

Aerated concrete does have disadvantages when it comes to fixing nails and plugs—you either need to use special aerated concrete anchors or pre-compress the hole with a thicker nail (there are also expensive templates offered by manufacturers for this). In other words, you don’t drill out the hole but compact the material around it to create a secure grip for a standard plug.

By the way, an 11.5cm (4.5 inches) aerated concrete interior wall has worse sound insulation performance compared to a wall made of laminated timber beams (KVH) with OSB/gypsum board and mineral wool filling (which we researched for our project).

Regarding cracking, you don’t need to worry because, as mentioned, the temperatures affect both materials almost equally from the inside.

The fact that aerated concrete is more expensive than ETICS may be due to the builder’s company philosophy — for example, if they have favorable agreements with the supplier for sand-lime bricks or work with prefabricated modular walls, or if they simply do not source aerated concrete often and therefore have no good purchasing terms. Since we don’t know what kind of ETICS was offered, it’s hard for us to judge—maybe the insulation values were also different after all?

Good evening,

Illo77 schrieb:

Don’t worry, this is often the case because calcium silicate blocks have more mass and thus provide better sound insulation, which is an advantage for interior walls. Furthermore, the thermal insulation benefit of aerated concrete between interior rooms is usually irrelevant, whether we are talking about an aerated concrete, timber frame, or clay block exterior wall.

First of all, the discussion was about aerated concrete in combination with bricks; I haven’t seen any mention of calcium silicate here.

Illo77 schrieb:

Aerated concrete also has the disadvantage when it comes to fixing nails and anchors: you either have to use special aerated concrete anchors or precompact the hole with a correspondingly thick nail (there are expensive templates for this from the aerated concrete manufacturers). This means you don’t drill out the hole completely but compress the material around it to secure a standard anchor.

Interesting – are special anchors not needed for hollow bricks? Or would you need a hammer drill for calcium silicate blocks?

Illo77 schrieb:

By the way, an 11.5 cm (4.5 inches) aerated concrete interior wall has worse sound insulation values than one made from kiln-dried structural timber with OSB/gypsum board and mineral wool insulation (we researched this for our build).

That’s correct!

Illo77 schrieb:

Regarding cracks, you don’t need to worry since, as already mentioned, the interior temperatures affect both materials almost the same way…

I would be interested to have your contact details so I can send any claims for damages directly to the right address?

Regards, Bauexperte

Interesting, no significant contribution to the original poster’s question at hand, but waiting to criticize others without providing a meaningful answer...

I simply assumed sand-lime bricks since I am not aware of any red aerated concrete blocks, and it is generally known that you should never combine red and white (or even yellow and white) materials, meaning no aerated concrete exterior walls combined with Poroton interior walls, for example, due to their different shrinkage behaviors. I expect the contractor to be aware of this... if not, he should consider selling lingerie instead. Sorry for not explaining this in detail... you can get the address, but I would rely on the general contractor carrying out the work according to the original poster...

The shrinkage behavior of aerated concrete and sand-lime brick is the same (at least for a well-known manufacturer like Xella). When building the aerated concrete exterior wall, leave flat anchors protruding for connection to the interior wall; if forgotten, use Wakai connection anchors afterwards (usually called aerated concrete drive-in anchors).

Apart from that, most sound usually passes through the door.