ᐅ Very thin screed with soil underneath – what to do?

In an old building (part of a farmhouse), the rear section is being renovated. After chipping out parts of the walls, especially in the bathroom, it became clear that there is approximately 8cm (3 inches) of screed. (Apparently, this consists of three layers, as it breaks in layers when chipped: two layers of about 4cm (1.5 inches) each, seemingly made of the same material, and a top layer of about 1cm (0.4 inches) – presumably a leveling compound.)

Since removing the floor to dig deeper and install insulation would be a lot of work, this option is being discarded. Installing insulation on the existing floor and then adding another screed layer would be possible given the room height of 3m (10 feet), but this is also avoided due to the effort involved. Since we manage around 30 hectares (74 acres) of forest and do not need to economize on wood chips or firewood, any potentially higher heating cost is not a concern. That is my current reasoning.

In the bathroom (7m² (75 sq ft)), the entire floor will be removed and redone because too much has been chipped out there. An electric underfloor heating system will also be installed beneath the tiles.

Here are my main questions: Is heating without insulation effective? What is the best floor structure for tiles? Is a simple screed (how thick?) with a decoupling membrane sufficient?

In the other rooms, there are some minor uneven spots. Should the floor be ground down or is it enough to apply a leveling compound?

Murkoff schrieb:

In an old building (part of a farmhouse), the rear section is being renovated. After some chipping out, especially around the bathroom lines, it was revealed that there is approximately 8cm (3 inches) thick screed. Apparently, it consists of three layers, as these break up in layers during chiseling: two layers of about 4cm (1.5 inches) each, seemingly made of the same material, and then a top layer of about 1cm (0.4 inches) thick—presumably a leveling compound.

To me, that sounds more like rammed concrete, and screed in the modern sense would only be what you refer to as the leveling compound.

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Murkoff schrieb:

Since it would require a lot of work to remove the floor in order to dig deeper and install insulation, this option is being skipped. Installing insulation on the existing floor and then adding another screed layer would be possible with the room height of 3m (10 feet), but this is also being avoided due to the effort involved.

You already have a huge amount of effort just to achieve a barely decent fix. So why not do it properly? Especially since you have the ceiling height to allow it. Where exactly is the additional big effort?

nordanney schrieb:

You already have a huge effort just to get a somewhat decent patch-up job done. So why not do it properly, especially when the ceiling height allows for it? Where exactly is the extra major effort?

Well, technically the patch-up is already there. So how should the new screed be installed on the rammed concrete? Floating? As thick as a standard screed? What layers and materials should be used?

Murkoff schrieb:

Well, strictly speaking, the botched work is already there.

You can't really say that, because depending on the house's construction date, that was the standard practice at the time. However, from today’s perspective, it can only be considered botched work if it is knowingly left as is, especially when you are in the process of renovating.

The main issue is the lack of a moisture barrier. This is not good for the building structure with normal heating habits. Depending on the region, such a construction can be extremely cold underfoot. It’s hard to compensate for this just by heating. You could install tiles at most, which would make the floor feel even colder. Electric underfloor heating is pointless without insulation.