As we know screeds must dry out before they are tiled on 1 mill a day is the guidline i assume this is to allow for shrinkage and moisture to evaporate, being slightly damp would not affect a cement based adhesive probarbly help a bit because a bit of suction so how is it OK to wet bed, laying on green screed and slurry as the screed will still shrink and the moisture needs to evaporate, just a thought.
Lucius.

The only time I'd lay on a green screed is if I used ditra matting or similar to act as a decoupling membrane. The adhesive would delaminate as the concrete cured (shrunk).
I would only tile on a screed that had been undercover for a min of between 6-8 weeks

Yes bighen i agree but wet bedding is a tried and proven method used by me and some other members of this group just wondered why that is OK for the reasons i gave, cheers Lucius.

Wet bed onto a mature screed is no prob

Wet bed onto a new screed would only be advised if using Dura-CI or Ditra, the structure of these menbranes allow shrinkage / expansion while allowing moisture to escape.

This help

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I dont think anyone is getting what i am saying Gary the Tiler has some photos of the wet bed way of laying tiles same as i do it again i am asking why it can be done this way with no probs for the reasons ive mentioned before. This thread has been moved where?
Lucius.

When you wetbed fix you lay your bed and slurry fix the tile directly to the wetbed as you go then it all sets hydraulicly together as one bed...

To tile onto a new screed after it has start to set is different...the bed has chemically started to set and loose moisture and started to cure/shrink etc...

So then you add adhesive to this which sets at it's own pace against what already setting underneath...moisture comes up and can debond what you have stuck with....

Not hard to understand really??????

No not hard to understand and i knew that anyway so what we are saying is that when wet bedding when the screed dries and possibly shrinks this is quite acceptable and will not affect the finish tiling.
Lucius.

Originally Posted by lucius

No not hard to understand and i knew that anyway so what we are saying is that when wet bedding when the screed dries and possibly shrinks this is quite acceptable and will not affect the finish tiling.
Lucius.

Wet bedding was the standard way of building a house floor in France for dozens of years. There is still a lot done i.e. the tiles pressed into a slurry on a wet screed. This has started to be replaced in the last 15 years or so with the advent of anhydrite flowing screeds and gypsum based tile adhesives. I guess as long as it is jointed sufficiently there is no reason to expect a problem. I guess jointing is the key to controlling curl as well as the bay sizes are relatively small. Placing the tiles in this way will actually help to minimise shrinkage as well becaue they will effectively act as a curing membrane. Remember that all cement based screeds should be cured for 7 days following installation but very few in the UK are so shrinkage is more of a problem than it needs to be. Having said that I am renovating my house at the moment and tried wet bedding 4" quarry tiles.....bloddy disaster. they have all delaminated. Won't do that again in a hurry.

Yea Ajax that was my thoughts that covering a wet screed with tiles would slow down the curing process, As Dave said adhesive is of a different constitution than a drying screed which as he said can cause delamination but then again so is a slurrry as it will have a much higher water and cement content than the screed so will set different and possbly affect the hydraulic bonding, ive never had any problem with wet bedding would be interesting to know what caused your problem.
Lucius.