Finch039
2023-11-13 08:21:34
- #1
The discussions, as I see it, always drift further away from the original question of the asker.
Basically the following:
In the bathroom, especially with timber construction of the building, the floors must be sealed so that in the event of an incident no water can penetrate under the floor construction. Just imagine the damage that would result if water flowed over the wall surfaces into the lower floors.
Now, as the asker explained, we have a walking surface made of gypsum fiber elements. The inspection and duty of care of the floor installer (here: tiler) therefore specifically refers here to a substructure which deviates completely from a usual mineral screed.
Such a construction must certainly be sufficiently and appropriately checked for possible deflections under point loads.
After all, in the event of damage, proof must be provided of which inspections were carried out according to which procedure – and what results were evident at that time.
Later simply being able to state "Everything was fine" will certainly not serve as an exonerating argument for the tiler in case of dispute.
In the simplest case, you place a longer straightedge on the unloaded surface of the dry screed elements and then load the surface with body weight. Deflections of a significant extent must not occur.
However, since there will definitely be deflections, especially with a wooden beam ceiling, the manufacturers of the lightweight construction specify the maximum tile size as 30 cm x 30 cm and recommend a flexible adhesive together with a flexible grout compound.
That about ceramic floor coverings.
Now let us turn to the preparatory work.
This consists of sealing the entire bathroom area, regardless of the water exposure class, with a suitable liquid sealant.
Anyone who at this point comes up with the idea of using a bituminous sealant should quietly sit in a corner and continue to passively follow the further discussion on this topic.
A bitumen sealing membrane indoors, especially on gypsum fiberboard (prefabricated screed), is a no-go!
After the floor area has been given its first sealing coat, the transitions to rising surfaces are integrated within about 12 hours into the second application of the liquid sealant using corresponding sealing tapes and system corner solutions. This application usually has a different color than the first coat so that any defects can be quickly noticed.
A decoupling mat mostly serves only the craftsman’s business because they like to pass on the costs involved to the frightened and thankful client.
That decoupling mats are only used for critical screeds should at least be mentioned here.
A floor level based on a (naturally suitable) gypsum fiberboard is not a critical substrate!
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So to sum up:
A seal, for example based on a brush- or roll-applied liquid sealant, together with sealing tapes on rising wall surfaces is absolutely necessary in timber frame construction of the building.
A decoupling mat is by no means one of the necessary building materials if new gypsum fiberboards are used as a "dry screed."
Flexible auxiliary materials such as tile adhesive and grout are also necessary purchases.
The tiles must not be larger than 30 cm x 30 cm; otherwise, with the unavoidable deflections (in dry screeds as timber beam ceilings), there is a significant risk of breakage or cracking due to usage loads.
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I hope I have been of service again with these hints!
Regards: KlaRa
Thank you very much for this detailed and above all question-related answer!
The dry screed elements were primed, then the decoupling mat was glued in flexible mortar. The inside and outside corners as well as the entire wall surfaces were sealed with a blue sealing tape. So everything is in order. The connection to the shower tray was also carried out properly.
I am only concerned about the deflection of the subfloor. It was sometimes already about 2–3 mm. I pointed this out to the tiler. His statement was: Everything is fine. The flexible adhesive adds so much stability to the subfloor that it doesn’t matter.
The tile format is now (unfortunately) 60 x 60 cm, laid with flexible adhesive in 5–8 mm (height differences) and grouted with flexible grout.
And I have my doubts whether this will hold permanently (and had already expressed these before). I hope we will see.
In case of damage, I only wanted to know whether I have claims if it does not hold.