Screed with drying accelerator: warranty?

Hello "Schubbiano". At least cement screeds dry to ready-for-covering maturity under good drying (i.e., on-site) conditions within about 6 weeks. Calcium sulfate screeds are faster; here one can assume readiness for covering within approx. 14 days. Additional costs: marginal. Nowadays, the so-called drying accelerators, i.e., screed additives, have become the "state of the art". Advantage: faster readiness for covering, disadvantage(s): some accelerators work, others do not to the expected extent, and furthermore: they are all special constructions that are not covered by the screed standards (I refrain from listing all of them here)! This means: the client must be extensively informed and give their consent to the installation! The warranty is – as already explained on this topic – naturally present; it is assumed by the screed layer. This MUST also pass on the information to the client, a) according to which method the residual moisture is to be determined, b) how the measurement is conducted, and c) from which achieved value the readiness for covering for which type of floor covering exists. --------------- That the additional costs amount to €1,000, I would ask the offeror again with a steady look in the eyes. Depending on the area size, it could only be that a rapid cement is to be used here. These types of cement are always (significantly) more expensive than normal cement, but also fall under "special screed" (duty to advise and consent of the client). The screed additives mentioned earlier are only added proportionally to the cement and as a replacement for the mixing water during the mechanical mixing process of the screed mortar. The additional costs incurred for additives are also not decisive, as they are relatively low. We will "never ever" reach €1,000 in additional costs there. ------------ Regards and good success: KlaRa

Thank you very much for all your feedback, some of it very detailed. That helps a lot. Great forum! :)

We are also behind schedule and the construction contract specifies cement screed. The general contractor now said that to save time we can also have calcium sulfate screed installed. There is no additional charge. I have read that this screed should not be installed in damp rooms, bathrooms, basements, etc. The problem is that as soon as it absorbs moisture, it will be damaged (turns into gypsum). Does anyone have experience with this or am I worrying unnecessarily?

I have read that this screed should not be installed in damp rooms,

You can do it, but then the professional sealing of the entire floor is all the more important.

We are also behind schedule and have cement screed specified in the construction contract. The general contractor now said that to save time we can also have calcium sulfate screed laid. There is no surcharge. I have read that this screed should not be laid in damp rooms, bathrooms, basements, etc. The problem is that as soon as it absorbs moisture, it will be damaged (turns into gypsum). Does anyone have experience with this or am I worrying unnecessarily?

Answer: We generally do not have damp rooms in living areas. As "nordanney" wrote, in bathrooms (but this does not only apply to calcium sulfate screeds) a surface waterproofing is advisable depending on the water exposure. In the basement, if there is only a floor slab (which also touches the ground and is not waterproofed on the rear side), i.e., NO screed on insulation, a foil waterproofing must be installed before screed installation. It should also be considered that thermal insulation must be installed if the basement space is to be converted from a subordinate use into living space. In most cases, however, this is likely to fail due to the available room height. Because about 10cm of insulation is necessary, plus screed of about 35mm to 45mm (depending on binder and material strength (better: flexural tensile strength)). What must be considered with CA screeds and floor-level shower trays is this: Either a modeling with cement screed must be done (which nobody does!) or a factory-made plastic shower tray is used. The rest of the floor area can then be sealed again with an alternative liquid waterproofing. Regards and good luck: KlaRa