ᐅ Exterior wall brick + interior walls calcium silicate blocks

Hello,

Our detached house is being built monolithically with exterior walls made of brick. It was originally agreed that the interior walls would also be made of brick, as it seems that certain disadvantages can occur with the "red-white" combination. However, the interior walls have been constructed with calcium silicate blocks instead.

I am now wondering whether this supposed rule—that one should use either "red-red" (brick-brick) or "white-white" (aerated concrete-calcium silicate) combinations, but not mix "red-white"—is actually a common misconception, or if there are indeed real disadvantages and medium- to long-term issues (such as cracks) to be expected.

We are still at the shell construction stage, so in principle, significant changes could still be made with considerable effort. However, the ceilings have already been poured with concrete, which makes replacing the interior walls quite difficult.

Thank you for your assessments.

Augustus

Hello Augustus,

“Agreed upon” sounds fine, but what does the contract say? There should be some kind of building specification that includes more details than just “1 house,” right?

Calcium silicate blocks are not something bad, but they have different properties compared to bricks (I assume Poroton or similar). If the interior walls are decoupled (slip joint) and not interlocked with the exterior walls, differing expansion won’t cause any problems. That’s a matter of the construction method.
In general—and without knowing the exact blocks—the calcium silicate offers better sound insulation due to higher mass, but poorer thermal insulation. However, what really matters is what was agreed on contractually.

If there are already such “misunderstandings” here, how about the masonry technique? Were the blocks laid wet (thick mortar bed) or with thin-bed mortar? What does the block manufacturer specify? In principle, the construction company is obliged to follow the “rules of the trade,” which includes proper installation. Do you have a building inspector or expert on site?

Regards,
AallRounder

Hello Allrounder,
thank you for your reply; I just noticed that I had phrased it incorrectly.
The contract states that the load-bearing interior walls are made of brick, and the non-load-bearing walls are constructed as gypsum board walls.
Yes, the exterior walls are made of Poroton. The interior and exterior walls are not interlocked; only these metal strips (I don’t know what they’re called) are installed to hold the two walls together.
What do you mean by a sliding joint?
We had considered hiring an expert.
However, after some “collisions” to put it mildly with one we engaged for a recently completed project, we decided against it for this project. The additional input the expert could provide was very limited. When I then received the offer for the requested supervision of the current project, the decision was quickly made.

So far, so good. The problem now is that the ceilings are already resting on the load-bearing walls...
I can hardly have the walls demolished anymore, especially since structurally it would never be the same as if the ceiling were cast directly onto the wall (you can never achieve the vertical compression prestressing in the load-bearing wall again).
I am currently trying to get an overall picture and assess how strongly I should “push the issue.”
On the one hand, I do want to set an example to ensure that from now on all contractual agreements are honored.

Regards,
Augustus

Hello Augustus,
only these metal strips (not sure what they are called) have been installed: those must be the sliding joints!

I don’t understand the part about the ceiling resting on something: it should actually only concern non-load-bearing interior walls here, meaning nothing should be resting on them. Because using gypsum boards as load-bearing walls would be problematic. For the load-bearing walls made of calcium silicate blocks instead of clay blocks, no changes should be possible anymore.

Compared to calcium silicate blocks, gypsum has better moisture storage and regulation properties. Either you have the non-load-bearing walls removed again or make some kind of deal, for example thicker interior plaster to compensate for the inferior properties of the calcium silicate blocks mentioned above plus a compensation payment. That depends on your negotiation skills. After all, the company did not stick to the contract.

Regards
AallRounder

Hello Allrounder,

So, what is contractually fixed is:
Load-bearing interior walls made of brick (these are already in place, but are now built with sand-lime bricks).
Non-load-bearing interior walls as drywall partitions (these are yet to be installed).
Of course, the load-bearing interior walls (actually sand-lime brick) were built, the ceiling was laid on top of them and then concreted, since the ceiling rests on these walls for support.

Regarding the wall connection:
About 15mm (0.6 inches) wide metal strips were inserted into the joints of the brick exterior wall, which then interlock with the joints in the sand-lime brick interior wall. I assume this was simply to secure the interior wall against tipping over. (Although I actually believe it wouldn’t move anywhere anyway, and if it wanted to, these few strips wouldn’t stop it.)

What I took from your first response, and which makes perfect sense, is that the joint at the plastering stage must be separated.
This could be done as follows: The inside surface of the exterior wall is plastered first and ends at the interior wall.
In the next step, once the plaster on the exterior wall is set, the interior wall is then plastered, and where the plaster of the interior wall meets the plaster on the exterior wall, a separation joint is installed. There is a material for this, which I can’t recall the name of right now, but it looks a bit like cork.

I think that should prevent any cracking. Or are there even systems using plaster beads or something similar?

Regards, Augustus

Hello Augustus,

Augustus schrieb:

Metal strips about 15mm (0.6 inches) wide have been embedded in the brick exterior wall joints, which then interlock with the joints of the calcium silicate block wall.

As I mentioned earlier, these are the movement joints I referred to, meant to decouple the walls.

The plaster can be separated in different ways: either the profile projects slightly into the plaster thickness, so plastering only reaches up to that point; or a permanently elastic joint is created; or simply a scratch coat cut is made. Your masons should know this better.

If you’re no longer planning to take action regarding the non-compliant calcium silicate blocks, you should at least supervise the installation of the gypsum boards. Calcium silicate is not ideal for the indoor climate (see my earlier response comparing calcium silicate and gypsum).

Regards,
AallRounder