ᐅ Installation height of HT pipes and aluminum composite pipes in the screed

Hello everyone,

I am facing the following problem:

I want to lay screed in the bathroom of my ground-floor apartment in a multi-family building from 1971, without underfloor heating. Unfortunately, the plumber has installed aluminum composite pipes and a DT50-HT pipe on the existing concrete floor. For the HT pipes, he slightly raised the concrete ceiling, but not for the aluminum composite pipes. The total floor buildup is about 8.5 cm (3.3 inches) including the tile surface. I planned to lay 6.5 cm to 7 cm (2.6 to 2.8 inches) of screed and then install a decoupling membrane from Schlüter, followed by the tiles. At the HT pipes and the overlaps of the heating pipes and the hot water line, the highest buildup is approximately 3.5 cm (1.4 inches). That would leave only about 3 cm (1.2 inches) for the screed layer. Below me is an unheated basement.

Now the question is how to best solve this. I have been thinking about it for days and trying to find solutions, but I can’t seem to make progress.

• PE foil + fast-setting screed applied directly up to 6.5 cm (2.6 inches), partially with screed mesh? Normally not allowed since pipes would be embedded in the screed.
• Insulation up to the top of the pipes + screed foil + screed? Probably won’t work because of the layer thickness — maybe with reinforcement mesh or screed wire mesh to prevent cracks, then decoupling membrane for the tiles? The concrete ceiling is also a bit uneven — I read that sandblasting would be necessary and quite elaborate.
• Bound gravel fill + reinforcement mesh + thin self-leveling screed?
• Bound gravel fill up to the top of the pipes and then foil with fast-setting screed? Probably not a good idea because of the thin screed layer.
• Bound gravel fill + screed boards? I don’t feel comfortable with that...

Composite screed is out of the question anyway. Maybe someone here can help me? I would be very grateful!

I would choose number 5. Why do you have concerns?

nordanney schrieb:

I would choose number 5. Why do you have concerns?

Thank you for your assessment! My concerns are about the long-term strength and durability.

I have another proposal after re-measuring:

6. Bound fill + PE foil + fast-setting screed, approved for a 30mm (1.2 inch) layer thickness on a separating layer.

I would fill the bound fill to a level that allows a 3cm (1.2 inch) screed to be applied, which would also just cover all the pipes.

Still prefer option 5?

I don’t see why a proven system shouldn’t be used!? Dry screed on a leveling layer is standard practice and has been used tens of thousands of times.

nordanney schrieb:

I don’t see why a proven system shouldn’t be used!? Dry screed on insulation is standard practice and has been used tens of thousands of times.

Even in the bathroom? Probably because of the waterproofing that you do anyway, right? I was more concerned about the tiles (30x60cm (12x24 inches)) and the shower tray.