Can exterior Poroton masonry and interior lime sand masonry be mixed?

Hello everyone,

for a 3-story monolithic construction, we are planning our house with a 42.5 Poroton exterior masonry. Either the S7 or S8, that is, a filled brick with increased web thickness and thus improved sound insulation, which is important to us.

According to our architect, although one tries to stay within the material for the interior walls because of the shrinkage and expansion behavior, calcium silicate bricks contribute to improved sound insulation inside. Therefore, he recommends calcium silicate bricks for the load-bearing (24) and non-load-bearing (11.5 and 17.5) interior walls.

I would be interested in your assessments/experiences on this:

1. What are your experiences with the combination of Poroton outside / calcium silicate brick inside?

2. Are there special constructive measures to be considered when implementing this mixed construction "Poroton / calcium silicate brick" in order to prevent possible crack formation?

3. The direct sound insulation index Rw for a 24 calcium silicate brick is 60.5 dB (see attachment), whereas it is 56.1 dB for a 24 Poroton hollow brick plan T. Is a difference of 4.4 dB significant?

Thanks and best regards!

Exactly that happened to us once. I then saw the damage that occurred. It is such that KS-MW shrinks, but fired bricks do not or hardly at all. At every junction of interior wall to exterior wall, cracks appeared in the plaster. You could tell from the cracks that the KS wall had given way due to shrinking. If you are not planning to use wallpaper, then I would avoid mixing the building materials.

Hello everyone,
for a 3-story monolithic construction we are planning our house

... unfortunately only with a single question, although this forum community can help better holistically.

1. What are your experiences with the combination Poroton outside / KS stone inside?
2. Are there special constructive measures to be considered when implementing this mixed construction method "Poroton / KS stone" to prevent possible crack formation?

I have no personal experience with this mixed construction method (tenant in a homogeneous pumice building), but I know it has been widely used by both general contractors and builders for a long time (which argues against problems). Constructive measures include, for example, mesh tapes in the plaster, but also expansion joints, which I personally do not consider a big deal, especially since they do not necessarily have to be conspicuous in terms of color.

3. The direct sound insulation index Rw for a 24 cm KS stone is 60.5 dB (see attachment), while for a 24 cm Poroton hollow brick flat T it is 56.1 dB. Is 4.4 dB a big difference?

The scale is not linear, which leads to misinterpretations. Practice and data sheets have so little in common that I advise my clients to avoid data sheets widely (and to trust the practitioners – also in the sense of not suggesting new methods to them).

We have 42.5 aerated concrete exterior walls. Inside we have aerated concrete of various thicknesses and [Kalksandstein] walls. [Kalksandstein] walls for the granny flat. I find [Kalksandstein] really excellent acoustically. I would use it throughout the whole house next time.

Furthermore, we have a soundproof door. It only cost an additional €200 and is really great. Note that it has a different frame and a bottom lip. Consider this beforehand as everything would need to be replaced.

If you are interested in soundproofing, you should also look into the concept of decoupling for [Rollladen] etc. You can hear those throughout the whole house.