Different screed method for ventilation system?

  • Erstellt am 2016-03-23 12:59:29

Bauen15/16

2016-03-23 12:59:29
  • #1
I hope you can help me. We had our central ventilation system installed on the concrete floor for structural reasons. Now the screed should be poured. As we learned from the screed layer last week, he has to apply the screed in layers, one centimeter each day. This is due to the many pipes of the ventilation system. It is a flowing screed. Then the underfloor heating is installed on top, followed by screed again. When I was at the construction site yesterday, I saw that 7 centimeters of screed were poured at once. When I asked the employees, they said they always do it this way. They had never heard of [Zentimeteraufbau]! When I tried to reach the boss, he said he was not there when the [Zentimeteraufbau] was mentioned. When I explained my concern, the employee said everything was fine. There is no other procedure. I must have misunderstood something. How can one misunderstand something like that? Unfortunately, our site manager is no help either. He gives the same answer, everything is correct. Now we are afraid that the screed was poured all at once due to time pressure. How was it done for you?
 

nordanney

2016-03-23 13:04:32
  • #2
The pipes were laid in the concrete ceiling with us, there was already a lot going on with the ventilation system, electrical work (spots + cables), and reinforcement. Everything was concreted in one go. I can't quite imagine now why screed should be applied cm by cm. What I also don't understand is why screed + underfloor heating + screed.
 

WildThing

2016-03-23 13:30:05
  • #3
Hey,

well, I've never heard of "centimeter-wise" screed either. For us, like at nordanney, the round ventilation pipes were laid directly on the concrete ceiling and poured over with concrete all at once.
Our floor structure on the floor was then as follows:
- Concrete
- Only in the basement bitumen membrane
- Empty conduits from the electrician and supply pipes for the underfloor heating
- Styrofoam (the pipes were cut out)
- Impact sound insulation + underfloor heating
- Screed, which flowed between the underfloor heating pipes and still covered them by a few centimeters.

How is the structure with you? Similar??
 

ypg

2016-03-23 13:43:43
  • #4
With us: ventilation ducts on the concrete ceiling, styrofoam, foil, underfloor heating pipes... Then the screed in one go – never heard of screed layers!
 

KlaRa

2016-03-23 13:57:03
  • #5
Hello questioner. The core question is certainly not "How was it done at your place?", but rather: Does the procedure correspond to a proper installation? Maybe you misunderstood something, I at least do not want to rule that out. Let's start like this: One screed is not equal to another screed! For example, if pipes and other installations lie crisscross on the raw ceiling, then that does not correspond to a situation on which one can pour a screed as a usable level and load distribution layer. It is possible that the lower layer was a so-called lightweight or leveling screed. This is made with cement, sand, and lightweight materials such as polystyrene additives. With this, the (of course firmly fixed to the concrete ceiling) installations are "buried" and a uniform level is created. On top of this (on the insulation layer) the "real screed" can then be poured or constructed. But neither the support screed nor the upper load distribution layer is poured "centimeter by centimeter"! In the case of underfloor heating, it may very well be that 70 mm nominal thickness was specified. We need 35 mm screed coverage for a CAF (which is a flowing screed based on calcium sulfate) over the high points of the heating elements. The minimum thickness for a heated CAF would be about 35 mm + 12 mm = 47 mm to 50 mm. If 70 mm thickness was poured, then this only affects the drying time and later the time until the heat "arrives" in the room after starting up. Actually, for this last reason, one gladly refrains from unnecessary extra thicknesses in heated screeds. --------------- Only if it is necessary, i.e., in individual cases, can screeds also be "layered" in slices. That means: after grinding the screed surface, prime it and pour 1 more screed layer. But this is only done if the load-bearing capacity of the load distribution layer - for whatever reasons - is not given - and the height necessary for layering is also available on site .... ------------------- I hope to have shed some "light into the darkness". Best regards: KlaRa
 

Bieber0815

2016-03-23 22:08:45
  • #6
More importantly: What is the planned floor structure for you? For us, from bottom to top starting at the raw ceiling: 8 cm insulation 3 cm impact sound insulation Foil Underfloor heating pipes on clips 7 cm screed around and above the pipes. In the 8 cm insulation layer are the flat ducts for ventilation (5 cm high) as well as electrical and water lines. It was a major effort to convince the tradesmen to work properly so that nothing protrudes beyond the 8 cm, preferably stays below (crossings are unavoidable). In the end, it was important that the impact sound insulation lies evenly and completely on the insulation layer and that there is no direct contact with installation elements below. Any empty spaces in the insulation layer were filled with bonded loose fill. The screed then goes on top, AFAIK with at least 45 mm coverage over the pipes (cement screed). This was met by us, just about.
 

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