Solid house: Which stone? Poroton, Liapor / expanded clay, Ytong?

Good evening,

I vaguely remember that you should stick to one type of stone and not use various kinds.

You remember correctly

Mixed masonry should be avoided whenever possible if you want to prevent cracks and thermal bridges. The building materials differ in their material-specific properties as well as in their shrinkage and creep behavior. The consequence of this is stresses in the plaster substrate, and due to differing thermal conductivity values, condensation can form on the interior walls.

Rhenish greetings

Construction expert was faster. 

We were advised against the aforementioned combination.

We are now building with Ytong. The walls are either load-bearing and accordingly in thickness or 17.5'. Only two walls were executed in 11.5 (shower/bathroom/laundry room and office/bedroom on the upper floor). Now that the interior plaster is applied, there is hardly any more sound echo. The drywall on the ceiling in the upper floor is still missing; it will be installed only after the screed has been laid and dried. We therefore do not expect major problems with the sound.

I have had painful experience with Poroton and sound insulation, as well as thermal bridges. If you simply screw a window or a door into Poroton or aerated concrete, the frame is insulated, but around it a perfect thermal bridge forms with a risk of mold. With calcium silicate bricks, more thermal energy is lost at local weak points in the insulation due to good thermal conductivity, but there is rather no local cooling of the wall and thus no mold. In addition, the window frame is usually integrated into the ETICS with overlaps. That does not mean that you can't do it properly with Poroton or Ytong, but special attention must be paid to this.

I would be interested to know if it is really as critical with Poroton and aerated concrete as it is presented here?

Different thermal conductivity values can cause condensation water to form on the interior walls.

You have to explain that to me. It is obvious that different mechanical behavior can cause cracks. Although I suspect that mechanical stresses can also occur within one type of building material (e.g., due to different loads and different RH or due to the different average temperature in the exterior walls). But if I build an interior wall of aerated concrete (KS) on an aerated concrete exterior wall, where should the condensate come from? The interior surface of the exterior wall is roughly 1 degree colder than the room air. The KS wall is about as warm as the interior air (assuming there are no thermal bridges at the floor slabs) and thanks to good thermal conductivity, the interface between interior and exterior wall is also roughly room temperature. So there is only about 1 degree temperature variation, and accordingly no condensation water. It would look different only if I built aerated concrete inside on a KS exterior wall.

Hello,

in advance - the language of the Internet is "Du"

You have to explain that to me ... But if I build with KS on the inside of a aerated concrete exterior wall, where is the condensation supposed to come from?

I consciously wrote "can" because, on the one hand, from my point of view, it belongs to a comprehensive answer. On the other hand, because there are aerated concrete, Poroton as well as KS with different thermal conductivities (depending on raw density). If you want further explanations on this, you will find plenty of information online; among others on Chemie.de, Fraunhofer Institute or also the University of Bochum. I am currently not a natural scientist, nor do I have access to this rather difficult language; "legal German" on the other hand is child's play for me.

I can assure you for our work that we always try to avoid mixed masonry; with the avoidance of cracking being the main focus. Those who absolutely insist on KS should in my opinion do so with full consequences and get used to an insulated exterior wall. Those who prefer a monolithic wall structure and are sensitive to noise can use proven lightweight construction in the attic, which additionally facilitates later conversions. With a 36.5 cm exterior wall - whether aerated concrete, Poroton, pumice or expanded clay - we hopefully are no longer talking about missing sound insulation.

To be honest, I don’t really understand this whole discussion about the material mix either.

Rhenish greetings

If you want further explanations on this, you’ll find plenty of information on the web; among others at Chemie.de, the Fraunhofer Institute, or also the University of Bochum. I am not a natural scientist right now,...

And I am a natural scientist and wonder about some things that are unnecessarily complicated on the technical application side.

On the other hand, since there are aerated concrete, Poroton, and KS with different thermal conductivities (depending on bulk density)

You will almost always have a higher thermal conductivity for interior walls than for exterior walls, and the (insulated) exterior wall will almost always have about room temperature on the inside. Therefore, I cannot imagine how condensation could form there. In addition, with Poroton, you usually use a denser clay brick on the inside, with better thermal conductivity. The only construction where one could deliberately cause condensation with an interior wall in butt joint (which is what we are talking about here, I thought) would be if a thick aerated concrete or Poroton wall is butt-joined to a thin uninsulated KS or brick exterior wall. That could possibly happen if someone installs aerated concrete inside a bathroom during an old building renovation.

I can assure you for our work that we always try to avoid mixed masonry; with the prevention of crack formation being the primary concern.

But a dumb question: What about non-load-bearing interior walls? Those can be decoupled, right? And theoretically, lightweight walls are mixed masonry anyway.

Anyone who insists on KS should, in my opinion, do so fully consistently and learn to accept insulated exterior masonry.

Which, in my layman’s opinion, is anyway the most consistent construction method (ideally combined with a ventilated curtain facade, which is of course not quite cheap) since you can best avoid thermal bridges.

Whoever prefers a monolithic wall construction and is sound-sensitive can resort to proven lightweight construction in the attic, which also facilitates later remodeling.

Or at least with Poroton inside one should build with smooth bricks RDK 1.4 or even soundproof bricks RDK 2, and also not skimp on load-bearing walls; unless you want to acoustically share everything from music to sneezing, coughing, and toilet use to lovemaking with all the house residents.

With 36.5 cm exterior masonry – whether aerated concrete, Poroton, pumice, or expanded clay – hopefully we are no longer talking about missing sound insulation.

At least not with exterior masonry in a quiet residential area.

A dumb question I don’t quite understand: Why do people always talk only about mass in sound insulation? Ultimately, it also depends on the damping by the material and the overall structure. Regarding the latter: If, for example, I have a load-bearing ceiling across the entire width of the house, structure-borne sound spreads much better than if I have a load-bearing interior wall. And a very stiff wall transmits sound better than a more damping material; a decoupled double-shell wall much less (can’t you do that at least with lightweight walls, with separated stud frames for both sides?).