ᐅ Ytong vs. Aerated Concrete Blocks – Construction Manager Pushes for Ytong Due to Incorrect Order

Hi everyone,

We are currently building our single-family house. The exterior walls are made of Hebel/Ytong 36.5cm (14.4 inches) aerated concrete. Originally, we planned to build all the interior walls with calcium silicate bricks. However, the builder pushed us to use aerated concrete for all the walls on the ground floor and only calcium silicate bricks on the upper floor where the bedrooms are located.

I wanted calcium silicate bricks mainly because of their high density and sound insulation properties, as I want good soundproofing between the bedrooms (3 girls).

Now the site manager clearly ordered Ytong, even though calcium silicate bricks are specified in the structural plan. Specifically, it states: KSL-P 12-1.60/DbM SFK12, raw density = 1.5 kg/dm³ (94 lb/ft³), compressive strength sigma0 = 1.80 MN/m² (261 psi), fk = 5.50 MN/m² (797 psi).

His mistake seems quite obvious. He now wants to sell the Ytong instead. He said that the PPF 0.5 Ytong actually has a higher density and provides better soundproofing than the calcium silicate bricks.

I’m not really familiar with this and would like to hear your opinions. Should I insist on using calcium silicate bricks?

Thanks.

Swoti schrieb:

He wants to sell with the Ytong now, of course.
He said the Ytong with a PPF 0.5 actually has a higher density and is better for sound insulation than the calcium silicate blocks.
Should I insist on the calcium silicate block version?

I wouldn’t even argue about it or worry about the specifications and so on. It all seems a bit obvious. He’ll probably come back with the "time factor" if rejected – reordering would delay everything, etc.

I would stick to what’s planned.

Thank you! You are actually right. It is also specified in the structural engineering plan. Even though it only concerns the interior walls on the upper floor, everything has been calculated accordingly. For this reason alone, I would rather not change it just like that.

I am sure that the local building materials supplier still has a few pallets of sand-lime bricks in stock, and the quantity should not pose any transport issues for a structural builder.

Swoti schrieb:

We are currently building our single-family house. The exterior walls are made of Hebel/Ytong 36.5cm (14 inches) aerated concrete. Originally, we planned to build all the interior walls with sand-lime brick. The builder then pushed us to use aerated concrete for all the ground floor walls and only sand-lime brick on the upper floor where the bedrooms are located.
I wanted sand-lime brick mainly because of its high density and sound insulation properties, as I want good soundproofing between the bedrooms (3 girls).
Now the site manager obviously ordered Ytong, although the static structural plan specifies sand-lime brick as well. [...] Should I insist on the sand-lime brick execution?

Definitely: yes!
Even though it might be a bit unclear in https://www.hausbau-forum.de/threads/weisse-wanne-wassereinwirkungsklasse-w2-2-e.45288/page-3#post-625370, the principle is quite simple: you should not put something heavy on something light. This applies especially where walls do not line up exactly on top of each other (and also considering that some of these are non-load-bearing walls).
Aerated concrete and sand-lime brick clearly do not have equivalent properties in the sense that they can be freely swapped.
The builder wants to build something different than what the structural engineer approved. This is not a minor offense. Aside from that, they must deliver exactly what you ordered according to your building contract. Nothing else — even if it were the same price — should be supplied by their subcontractor.

Even if it sounds harsh, it cannot be said often or clearly enough: the contractor’s “site manager” is, from an interests perspective, an opposing site manager. Their job is to protect their employer from delays and complaints—which from their point of view can come at unlimited cost to your interests. If you were unwise enough not to appoint your own site manager as the client’s representative against the contractor’s site manager, you should at least now set firm boundaries and enforce strict adherence to the building contract. Call fouls—issue yellow cards. Not acceptable!

It’s best to book two additional inspections with your independent building expert immediately. From experience, this will probably not be the last attempt to test your uncertainty and/or goodwill.

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For soundproofing alone, I would insist on using calcium silicate blocks.