Tiles loose under stair supports

Hello Matthias. The edge chamfers, which ultimately led to a flank tear of the elastic sealant between the baseboard tiles and the tile surfaces, are due to overnight drying of the screed and its associated re-curling towards the insulation layers. You only mentioned in your post that the tiles were hollow. However, with large tile formats, as I can see from the photos, at least when the tiles are laid using the thin-bed method, there cannot be a 100 percent support and thus not a 100 percent backside wetting of the tiles. This would only be possible when laying with the medium-bed method due to the greater adjustment possibilities. This is simply because the tolerance-compliant unevennesses of the substrate argue against it with the larger formats. So if the large-format tiles are only partially (35 % to 40%) hollow, that alone would not be a reason for concern. However, it could become problematic if the tiler did not perform a residual moisture measurement on the screed before carrying out their work. But I do not want to open another issue at this point! It should therefore be noted that the flank tears of the elastic sealant under the baseboard tiles are not a cause for concern and occur in many other new buildings. That is why such joints are also referred to as so-called maintenance joints, the ongoing inspection and, if necessary, renewal of which are the responsibility of the builder or the user of the property.

Hello KlaRa,

thank you very much for your detailed response. However, tearing off the maintenance joints is not an issue for me here. The tiler is supposed to renew them shortly. In doing so, I also want to have this unsightly edge somehow removed.

However, a concern for me is the loose tiles. It is clear that due to the shrinking of the screed, the tiles "sink" relative to the skirting board and the maintenance joints. What is strange, however, is that the first row of tiles directly in front of the front door behaves differently. If you look again at the photos, the first row consists of four tiles. Of these, the ones on the far right and far left (the ones at the back under the stair support) have this edge and are hollow. When you step on them, the tile clearly cracks. You notice this when stepping onto the second step of the stairs.

In my view, the screed and tiles form a panel, so I would expect the shrinking to also affect these tiles. But it did not; instead, they have detached from the screed. From my perspective, this constitutes a defect, as the adhesive mortar does not guarantee sufficient adhesion of the tiles.

A CM measurement was carried out and the residual moisture at that time was below 1.5% in all rooms. The architect then declared the floor ready for covering. Which, in my view, is also acceptable.

Best regards Matthias

This, in my view, represents a defect because the installation adhesive does not provide sufficient adhesion of the tiles.

Without any doubt, this is a defect!

... CM measurement was carried out ... residual moisture was below 1.5% in all rooms at the time.

Well, this value is hard to believe. Because, firstly, you only reach about 1.5 CM-% with a cement screed if it is a heated screed, and if it were a calcium sulfate screed, the value you specified as ready for laying is in any case too high! Furthermore, the flank fractures of the sealant unequivocally indicate that an overnight drying of the screed with re-wetting took place. This also cannot be the case with 1.5 CM-%. So something is definitely amiss. Presumably (as my professional experience shows) it is the CM measurement report which does not reflect reality.... Now several days on a business trip, regards: KlaRa

It is a heated screed. I cannot answer the other question. However, the value would be recorded by the architect in this way. Measurement is carried out centrally in each room via measurement points embedded in the screed. Finally, the question that is actually crucial for me remains. Is there any way to somehow fix the loose tile under the support of the staircase?

The answer is: without extensive destruction of the tile only by injection. However, the cause of the detachments is still unknown, which is why this method is to be rejected. Reason: Without knowing the cause of the damage, a "repair into the blue" is not sensible.

Hello KlaRa,

absolutely understandable. But what possibilities are there to investigate this if I cannot really remove the tile without touching the staircase?

Regards
Matthias