Leveling cast asphalt screed of varying heights

Hello everyone,

we have a cast asphalt screed that shows about a 5 mm difference in floor heights over a 40 m2 room.

Channels are milled into the cast asphalt and pipes for underfloor heating are laid.

Now our screed person wants to level the floor heights. Filling would be the thinnest method but expensive. He would now apply (calcium sulfate, because the expansion should be like that of cast asphalt) floating screed. However, the total floor buildup would be about 15 mm even at the high points.

My question is, how important is it to use another material to level here and why is the leveling actually so important?

Thank you very much!

For God's sake: Who tries such a thing????
Cast asphalt screeds usually have a thickness of about 35mm in residential construction.
Heating elements are usually about 12mm thick.
Apart from the fact that the heating elements in cast asphalt heated screeds are made of heat-resistant copper and embedded in the brushable bitumen mass, a screed thickness of only about 35mm - 12mm = 23mm results from a non-recommended subsequent installation.
What obviously arises here is a special construction for which there is no evidence that it will work in practice.
Far from the applicable professional rules!!!
What will happen?
Well, bitumen, the binder of every cast asphalt screed, is ultimately always a viscous mass in contrast to mineral screeds, which tends to flow under the influence of temperature.
As soon as milling is done in the bituminous existing screed, predetermined breaking points will be created there!
Reworking with a mineral leveling compound will also "finish off" the cast asphalt screed.
Even if it is – as stated – supposed to be a calcium sulfate leveling compound.
That will not work – floor damage is programmed, the total damage to the entire screed and now presumably newly installed heating technology as well.
What is being planned here – by whoever – is doomed to fail after the first use! Without any doubt.
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In the hope that my lines will be taken into consideration (otherwise we will probably see each other at a court site inspection for evidence collection):
KlaRa

In the hope that my words will be taken into consideration

Even as a non-thread starter, I found the explanation interesting. Are there alternative procedures if there is a cast asphalt screed in the existing structure, or would it usually be completely replaced?

Even as a non-thread starter, I found the explanation interesting. Are there alternative procedures if a cast asphalt screed is present on site, or would it usually be completely replaced?

Certainly, there are solutions!
Depending on the local situation, the cast asphalt screed can be partially removed on both sides by, for example, a total of 30-40 cm.
The "gap," meaning the resulting defect, is professionally and properly ramped.
What sounds so simple is associated with certain craft-related difficulties, because cast asphalt is installed on an insulation layer in residential construction, making the area around the defect ductile. If a filler were simply applied, the flanks on the left and right sides of the cast asphalt surfaces would tear under load. And so-called "nailing" would also be pointless because it cannot work with cast asphalt.
But in this case, as a special construction, the insulation layer level in the defect area could be completely removed, a composite construction to the concrete slab could be made with a reactive resin mortar, and the two cast asphalt surfaces (resting on insulation) could be connected with an approximately 8 mm wide movement joint.
The joint could later be filled with an elastified reactive resin (before the floor covering work).
Disadvantage (if one wants to see it as a disadvantage): The two joints would have to be incorporated into the top covering – not necessarily in the width of the movement joint.
This is also a special construction, certainly, but it would work (unlike the subsequently installed heating elements)!