concrete setting times?

[RockCeramics]

Could do with some info if possible relating to concreting.
A contractor is reinstating a concrete slab infill of 40m long and a depth of 350mm before a screed bed for tiling.
they are insisting that the screed bed will be fixed in 24hrs after concreting??
Now i assumed that the concrete would need to set before tiling, 1 day per inch is this correct, or are we looking at a longer period (3 weeks?)

 

[Ajax123]

If I understand this correctly they are laying 350mm of concrete then leaving it to set overnight before screeding. Assuming it is a 65mm (or thereabouts - Minimum 50mm) screed then what they are doing is ok provided there is a reasonably good key to the concrete surface and it is hard enough to take the traffic to lay the screed. The cement in the surface of the concrete will still be relatively reactive at that stage and so will promote an excellent bond with the screed. It will also still be relatively wete so will not pull the water out of the screed too quickly to prevent a bond failure.The one draw back with what they are proposing is the drying time as the screed going over the top of the concrete will impede the concrete drying and they will have to wait quite a long time for the whole system to dry.

The other thing to make sure of is that there are joints in the concrete reflected through the screed. At 40m long I would recomend at least 5 joints at around 8m spacings.

 

[DHTiling]

So they are asking for you to wet fix whilst screeding..?

Have you fixed this way before and also there is the probs with Efflorescence in the grout joints..