How long to wait until tiling onto 75mm screed

[ashurst]

I am having wet underfloor heating installed on top of 150mm insulation. The screen will be approximately 75mm. I will be laying 10mm porcelain tiles. How long should I realistically wait until tiling onto the area as I am reading conflicting things.

I am hoping that 21 days should surfice

 

[J Sid]

commission the ufh, use ditra uncoupling membrane or similar at 21 days I'd do or wait 80 days

 

[Chalker]

Leave 7 days after laying.
Commission ufh and put on low for as long as it takes to dry.
Sand floor to remove latience a few days after heating is turned on ( will set like rock if left any longer) this also helps drying times, a the polymers act like a plastic , trapping moisture.

When it's dry, turn off heating and tile.

 

[J Sid]

Leave 7 days after laying.
Commission ufh and put on low for as long as it takes to dry.
Sand floor to remove latience a few days after heating is turned on ( will set like rock if left any longer) this also helps drying times, a the polymers act like a plastic , trapping moisture.

When it's dry, turn off heating and tile.

sand and cement?

 

[Chalker]

sand and cement?

Never though of that.
TBH, at 75mm it must be sand and cement

 

[J Sid]

Never though of that.
TBH, at 75mm it must be sand and cement

you'd of hoped so but you never know

 

[Spacey]

Good chance it's Anhydrate or simlar

 

[J Sid]

Good chance it's Anhydrate or simlar

why?

 

[hmtiling]

Good chance it's Anhydrate or simlar

very deep for gypsum based. optimum for those is around 45mm i believe

 

[Spacey]

very deep for gypsum based. optimum for those is around 45mm i believe

Yeah doesn't mean it couldn't be though.
It's the most commonly used screed these days over UFH And builders as we know don't always follow the rules.
Could just be a fibre reinforced screed but Id want to be sure what I'm dealing with before laying anything.

In answer to the original question With UFH commissioned and running It's possible to dry it out in about two weeks

 

[hmtiling]

Good chance it's Anhydrate or simlar

better chance it's sand cement at that depth. when's the lino forum back btw

 

[Dumbo]

Yeah doesn't mean it couldn't be though.
It's the most commonly used screed these days over UFH And builders as we know don't always follow the rules.
Could just be a fibre reinforced screed but Id want to be sure what I'm dealing with before laying anything.

In answer to the original question With UFH commissioned and running It's possible to dry it out in about two weeks

You shouldn't force dry s&c screed

 

[Sean Kelly]

If time is an issue and cost is not an issue then use Ardex A38 (Ultra Rapid Drying Cement for Internal & External Screeds).

Screed the floor and tile after 4 hours. I believe it works out at 1.5 times more than the cost of normal screed.

I have not used this product myself, I got the info from asking the Ardex reps at a trade day.

 

[Old Mod]

There are several additives/Hydraulic Binders available that can provide you with a dry screed in 48hrs. Mapei topcem being one of them.
Even you can work on @Spacey After 4 days.

http://www.mapei.com/public/GB/products/207_topcem_uk.pdf

 

[Flintstone]

Bet this chap doesn't know if he's coming or going now

 

[ashurst]

Sorry for not replying earlier to clarify.

It will be a sand and cement mix. I honk I will go with the 21 days and ditra or similar. Bal do something called rapid Matt and it's only 1mm thick whereas ditra seems to be 3mm thick. Similar prices. Which should I use ?

 

[J Sid]

ditra will let water out, bal does not. So must be ditra

 

[hmtiling]

Or durabase

 

[NZ_Tiler]

Generally what moisture content should screed have if a decoupling matt is going over?

Would it not be similar to tiling?

IMO 21 days for a screed that thick is not long enough with regular sand n cement.

 

[Dumbo]

If I remember rightly Schluter claim it can be tiled as soon as weight bearing . I stand to be corrected and if I was doing this I would obviously check .

 

[Old Mod]

If I remember rightly Schluter claim it can be tiled as soon as weight bearing . I stand to be corrected and if I was doing this I would obviously check .

The phrase they like to use is,
'as soon as its mechanically repairable'
Tape the joints for moisture sensitive stone, otherwise not necessary, but certainly doesn't hurt, personally I'd prefer it.
But yes as soon as its load bearing.

To fast track a screed a 'vapour equalisation barrier' must be used i.e.
Ditra 25
Durabase mat

These mats are not for wet ufh obviously, but they still do the same job as above.
Ditra E Heat mat
Variopro ufh mat.

 

[slythetiler]

i treat S&C screed beds over UFH the same way as concrete 1 week per inch to dry, so at 75mm i would leave at least three weeks and not force dry it by using the UFH. I prefer to let it dry naturally. Then go with Ditra or durabase for crack suppression.

 

[gazmcd72]

You could always use bal green screed if time is an issue

 

[Flintstone]

You can tile on a green screed after 28 days using tilemaster ultimate but that doesn't offer any uncoupling if you want that.

 

[hmtiling]

Think bal green screed is 48hours. Most s2 adhesive are good for green screed too

 

[Andy Allen]

Is green screed flexible enough for the ufh..?

 

[Old Mod]

Is green screed flexible enough for the ufh..?

Maybe not on a green screed.

 

[Flintstone]

you could probably used ultimate to stick crack mat down then tile with ultimate on top of that. Cheaper than ditra

 

[Flintstone]

I would Always want to put some sort of uncoupling on a green screed

 

[Old Mod]

you could probably used ultimate to stick crack mat down then tile with ultimate on top of that. Cheaper than ditra

Antifracture mats are not suitable for use as a vapour barrier Andy, needs to be a product similar to Ditra or Dural. They allow moisture to escape via the cavities.