Tiling over new screed

[simon87]

I'm new to the forum so apologies if this is an old topic of discussion.
I have just had a kitchen extension floor screeded (sand and cement screed ) to a depth of 75mm. There is underfloor heating which has been pressure tested and is still under pressure at the moment, but not yet fully commissioned. My question is how long before it is safe to tile over the floor? I have read that drying times are 1mm per day which would mean 10weeks. What would happen is tiles were laid before the screed was fully dry?
I have also seen on a few threads that Ditra mat may mean that tiles could be laid earlier. How much earlier?
BTW: the tiling needs to extend into the old kitchen which is part screed floor part suspended timber floor.
Any advise much appreciated

[suave]

[Ajax123]

You must comission and run the heating first this can be done after 21 to 28 days. You can use fast track methods to tile earlier but ideally the screed should be dried. This as you say takes about 10 weeks. Tile before the heating is run and you will be dealing with a failure

[Mike]

you will also have to have a transition joint/expansion joint where the wood floor meets the concrete floor. you may be able to disguise this as your grout line and use colour match silicon for the joint

[simon87]

You must comission and run the heating first this can be done after 21 to 28 days. You can use fast track methods to tile earlier but ideally the screed should be dried. This as you say takes about 10 weeks. Tile before the heating is run and you will be dealing with a failure

Why is this? How long duseoes the UFH need to be run for? At normal work temperature?

Will running the heating not dry the screed out too quickly?

Thanks

[Dave]

As long as it is 21 days old or more then you can commission the heating, this is to put heat into the screed which in turn when heated will expand.. a new screed with in-screed heating needs to be heated firstly to allow this to happen, you do not want a screed expanding with a newly tiled installation and thus blowing the tiles off the surface with shear stress..

Once the screed has had it's first initial heat and any stress associated with first heating of it will be dealt with and thus tiling can commence.

But is it worth bearing in mind that cement based screeds are also prone to curling within the first few months so the use of an anti-crack/uncoupling membrane is worth thinking about.. taking the stress out of the installation..

Also once the 21 days are up then no.. using the heating will not premeturely dry out the screed, as at 21 days it will be fully cured to allow the heating to be turned on and this process also has to be done slowly.. turn the heating on at lowest point, that is normally room temperature and then you increase this in increments of 5dgs a day till at operating temperature recommended by manufacturer and then run at that for 3 days before allowing to cool down..

[simon87]

Thanks for the great advise.
Not to labour the point, but just to make sure I've got it clear; after 21 days and I've heated the screed up as described and let it cool, I should be 'safe' to tile. Even though the screed hasn't had its 10 weeks to fully dry?

Am I correct in assuming the un-coupling membrane mentioned is Dirtra mat (or similar)? I take your point re a stress free installation, I'm all for a stress free life!