Screed advice please

[Unregistered]

Hi. I am building myself a new house which includes one very large room - 10m x 6m with underfloor heating. I am intending on putting down Porcelanosa Par-ker Venis tiles which are 1.2m x 19cm. I am having conflicting advice as to what screed would be best, what preparation is needed, timescales and whether a decoupling mat is required. Any advice? I will have around 6 weeks between screening and tiling available.
Thanks

 

[bugs183]

Wait for Ajax to look at this, he really knows his stuff!!!!
As for an uncoupling mat, i would always recommend one if tiling a floor with underfloor heating, even with what i guess is a porcelain tile.
I use Ditra, Dural are cheaper, but i'm more confident using Ditra, for no reason i can explai

 

[Ajax123]

FOr a room that size I would have to say anhydrite is the best screed. It works exceptionally well with underfloor heating and assuming you only have one single zone you will not require any movement joints in the screed. In terms of time scales you can force dry the screed quite aggressively after a week and assuming a depth no more than fifty mm I would anticipate that it should be dry by the end of the commissioning phase of the heating. You could if you wish look at the thermoplane underfloor heating system which my company is involved in. This allows a 40mm screed instead of 50mm so you get to further bulk up the insulation for a given zone.

Preparation for tiling would be simply sand the surface Lilly to remove any surface debris dirt and loose laitance that might be present, check it is dry and then tile using a gypsum based adhesive. These generally would not require a primer. De coupling would be optional unless they are natural stone then I would deffinitely de couple. I say it is optional but in all honesty given the size of tiles it would probably not be a bad idea anyway.

Yu say you are getting conflicting advice. What advice are you getting and what is being claimed about the various options you have no doubt been offered.

 

[Unregistered]

Thanks for all of this. One tiler says he never trusts anhydride screed as the tiles often do not fix properly, while another says he only ever suggests it. The first says he always prefers sand and cement, but as this is likely to crack with ufh, he would suggest matting at £10/ metre plus fitting. Considering the amount if tiling, this will add about a thousand pounds to the job. This seems a lot but would pay it if necessary. I did have anhydride screed in my current house and have not had any problems with limestone floor. My new tiles will be ceramic.

 

[Ajax123]

Thanks for all of this. One tiler says he never trusts anhydride screed as the tiles often do not fix properly, while another says he only ever suggests it. The first says he always prefers sand and cement, but as this is likely to crack with ufh, he would suggest matting at £10/ metre plus fitting. Considering the amount if tiling, this will add about a thousand pounds to the job. This seems a lot but would pay it if necessary. I did have anhydride screed in my current house and have not had any problems with limestone floor. My new tiles will be ceramic.

I would suggest that the fact that your existing house is anhydrite with no issues speaks more about the tiler than it does about the screed. Sticking to anhydrite is smple provided you follow simple guidelines. One of those is to use non cement based adhesive. If you are using ceramics there is o absolute need to uncouple although Id say this would be very belt and braces. Sand cement screeds do crack and should be reinforced to help limit the cracking. They should also be cured under polythene properly which also limits cracking and curling. If you go anhydrite I would be happy to support you technically.... I am technical and specifications manager for the largest manufacturer of these screeds in Europe. I sort of hope I know what i am talking about generally. I would also happily offer my services technically to the tilers as well. Of course if you go sand cement that is your choice and I will still advise through the forums anyway.

For me though the decision between sand cement and anhydrite in a project ofthis size and nature is a no brainier...... Anhydrite every time. It will also save you money on your gas bills in the long term

 

[adros88]

Hi. I have a two week old sand and cement screed (75mm deep) with wet underfloor heating installed. I'm currently getting quotes to tile it. I've read that a de-coupling mat should be used but as with the original post on this thread I have had different opinions. We have chosen a porcelin tile. The only thing that is agreed on is that the screed isn't a great level so they all want to latex it first.

Any advice on drying times and the use of a matting would be really helpful.

Many thanks