ᐅ Calcium silicate block with cavity: Which fasteners are suitable for a balcony solar power system?
Created on: 8 Jan 2026 10:53
F
Felix571
Hello.
These blocks are supposed to have been used in my building. When drilled from the inside or outside, there is a cavity after about 4 cm (including plaster) deep. The drill dust is white, so it is probably calcium silicate brick. Unfortunately, I did not measure the depth of the cavity. I also asked our local building materials supplier what these blocks might have looked like back then, but they had no knowledge about that. And whether the blocks shown on the internet represent the original structure?
It would be great if someone could help me with this.
The reason for my question is that I want to install a balcony solar power system on the wall. With such a large cavity, this might be difficult.
I am also unsure about the mounting options for the solar power system. I have been in contact with many sellers regarding the wall mounting. They send drawings that do not provide any clear information. After further inquiries, they go quiet. Does anyone have more details about the mounting points on the wall?
These blocks are supposed to have been used in my building. When drilled from the inside or outside, there is a cavity after about 4 cm (including plaster) deep. The drill dust is white, so it is probably calcium silicate brick. Unfortunately, I did not measure the depth of the cavity. I also asked our local building materials supplier what these blocks might have looked like back then, but they had no knowledge about that. And whether the blocks shown on the internet represent the original structure?
It would be great if someone could help me with this.
The reason for my question is that I want to install a balcony solar power system on the wall. With such a large cavity, this might be difficult.
I am also unsure about the mounting options for the solar power system. I have been in contact with many sellers regarding the wall mounting. They send drawings that do not provide any clear information. After further inquiries, they go quiet. Does anyone have more details about the mounting points on the wall?
11ant schrieb:
Your picture and description don’t match – I recommend consulting an architect experienced in renovating existing buildings before continuing with what sounds like extensive remodeling work. You described drilling into a calcium silicate hollow block stone of size 300, so according to your description, you would have encountered a cavity after about 4 cm (1.6 inches) of material.
However, the photo shows a rather unusual free-standing construction (note the shut-off valve in a riser pipe through a lintel (?)) of a wall leaf made only of stretchers in a 2DF format. That does not sound like hollow blocks but rather almost solid bricks with just a lifting hole, and a double-leaf wall. That could easily reach the mentioned 28 cm (11 inches), and depending on the drilling location, you could indeed have hit an (egg-shaped) lifting hole after 4 cm (1.6 inches). Even a 15DF hollow block would not have a chamber and web structure similar to a porous brick but rather an oval cylindrical lifting hole plus several circular cylindrical hollow chambers. So, you should have your house examined by a structural engineering expert rather than relying on the original building description. Blondi may not be bricked in there, but it definitely sounds like a Pandora’s box. A 30 cm (12 inches) thick external wall would be almost avant-garde for the building year, as would building it from calcium silicate hollow blocks. If built monolithically from calcium silicate, it would most likely be made of 2DF stretchers and 3DF headers. On the other hand, your picture only shows 2DF calcium silicate stretchers and you mention bricks and an overall thickness of 28 cm (11 inches). This suggests a double-leaf construction, likely with 2DF brick stretchers on the outside, 2DF calcium silicate stretchers inside, and between them an (unfilled?) 5 cm (2 inches) air gap. So, as you see, it’s worth a detailed investigation—not just to hang a few small fixtures. Why not show the drawings from the building files? First, for clarification: The house was built in 1955 (with 30 cm (12 inches) calcium silicate hollow blocks), and the extension we’re discussing is from 1958 (using 24 cm (9.5 inches) hollow blocks). I acquired the building some time ago. It was originally constructed by a father and son, both masons, who were quite resourceful with using leftover materials and so forth.
Since there was originally a balcony above this section of the wall, it’s possible that the upper courses of bricks are made from different bricks than the lower ones. In any case, the wall is about 29 cm (11.5 inches) thick, including plaster on the exterior (not smooth plaster) and interior. If I wanted to investigate the wall structure, I would likely have to remove some plaster first. The fact that I consistently encountered a cavity after 4 cm (1.6 inches) drilling might, of course, just be coincidence.
11ant schrieb:
The photo shows a rather unusual free-standing construction (note the shut-off valve in a riser pipe through a lintel (?)) That is not a shut-off valve; it’s an electrical outlet that was there. The cable doesn’t come from above but from the side (extension from 1958!). There is no lintel above; that is Heraklit (a type of insulation board). Although, it’s possible that the Heraklit is hiding a lintel behind it. Originally, there was a large window planned up to the right wall, and why it was newly plastered (mortar category 3??), I have no idea.
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