Expansion Joints & Undefloor Heating

[Tilesponge]

Hi All, my first post, be gentle...

I am having the ground floor of my house tiled with 600 x 600 polished porcelain. It's going to be a continuous job from the sunroom (5m x 7m with plumbed underfloor heating) through to the kitchen (3m x 7m), utility room (3m x 2m), back hall (2m x 2m) and front hall (1.5m x 7m). Adhesive is Technik Rapid Set Flexible.
The sunroom is new and we have been drying out the screed floor slowly for the last month. As expected some cracks have developed.
My first question is whether the porcelain tiles might crack in the same place as the screed when they are laid. Do I need to take any precautions?
My second question is whether I need any expansion joints at the doorways between each of the rooms and indeed in the large tile field in the sunroom?
Thanks for the help!

[jay]

welcome might help if you post some pics of the cracks in question whats the make up of the screed and is there any joins in the floor has the ufh been commisioned yet

[Tilesponge]

IMG_1467.jpgIMG_1468.jpgIMG_1469.jpg

Thanks Jay. The first photo is the entrance between the original house and the new sunroom. I am most worried about the tiles cracking at this joint. The other two photos are the hairline cracks on the sunroom floor. The heating is fully commissioned and has been left on at 18 degrees C for the last few weeks.
The screen is 80mm sand/cement over 100mm of Kingspan insulation board.

[jay]

thanks take it the floor was commisioned straight up to temp or was it brought up slowly

[jay]

by the looks of the pics the first one needs to be an expansion joint carried through to tile finish recommend you cut the screed in a strait line (dont cut ufh be careful) this will help to control the movement the other pics show deff cracks not what i would call shrinkage cracks best bet is to use Ditra matting over all floor area to be tiled (others may be able to recommend other brands) as for other expansion joints best to let your tiler determine were they go
hope this helps

jay

[Tilesponge]

Thanks Jay. The heating could have been brought up a little slower than it was and this probably caused the cracks. Sadly, there is no budget left for Ditra matting over the whole area (100 sq m). So, I'll go for a 'proper' expansion joint at the sunroom entrance and mastic instead of grout at the other doorways. Would a 1m wide strip of Ditra over the joint in pic 1 help? Do you know how long the UFH should be left off after tiling? The Rapid Set bag says 4 weeks but this seems extreme.
PS Just found Tasmania on the map. Amazing to be getting tiling advice from the other side of the world (I'm in Ireland)!

[jay]

wouldn't recommend doing tiling unless you can afford ditra as cracks will more than likley come through best to wait until it can be done right a bit of ditra on exp joint would help but may cause issues with thickness if you dont do the rest follow instructions on your adh they all vary if not sure contact manufacture
yes on other side of globe but always willing to help

jay