Porcelain Tiling To Calcium Sulfate Based Screeds (Revised Dec 2011) - TilersForums.com

[Luggsey]

Hi has anyone got the text of this TTA technical document I can have a look at?
Tiling To Calcium Sulfate Based Screeds (Revised Dec 2011)
I'm starting my 150sqm porcelain install soon and want to make sure I haven't missed anything.
Cheers.

 

[Ajax123]

I helped write it so what do you need to know

 

[Luggsey]

Hi Ajax, I was trying to be 100% sure I was doing this right.
I have a calcium Sulfate new floor, laid 3 years now (long story) and I have cold UFH, that is pressurised but not hot yet.
I need to crack on and lay some 600x600 porcelain in one room and en suite so part of the house can be used before the rest is completed.
So what I need to know is:
Do I need a expansion gap after xM of continous run? If so what to use? This room through to en suite is 6m.
I have the mapi primer for calcium sulphate and the recommended mapi adhesive and grout. Is there any special requirement for 10mm porcelain laid on calcium sulphate, such as adhesive thickness, is a 5mm gapped trowel OK?
Thanks if you can help me.

 

[Ajax123]

These are general tiling questions and not to do with calcium sulphate. The UFH must be comissioned and run before tiling. The screed needs to be clean and free from loose friable material and needs to be absorbent. This means lightly abrading with a sander and vacuuming.

600x600 will need to be back buttered and grout gaps no less than 3mm. Maximum vay size for the tiles is 40m2 with max bay length of I beleive 8m butthat needs checking. Joints can fe either proprietary formers or dry jointed and siliconed with colour matched silicone.

The screed must be dry below 0.5% or 75%rh and should be tested so.

Not sure of trowel notch size but that will be set by the adhesive nit the screed.

 

[Luggsey]

Thanks Alan, I would have gone with 2mm gaps so will go with 3mm now.
The heating is pressurised but I can't run it?
I was hoping after 3 years there is no moisture there to speak of.
So do you need the floor to be 'warm' to lay the tiles?

 

[Ajax123]

The rules for underfloor heating are the same for all screeds. It should be cokussiobed and run. If you don’t you run the risk of thermal expansion cracking the screed and the tiles.

You say it’s had 3 years to dry… it’s also had 3 years to get wet again.

The heating should run through its commissioning cycle and then switched off for 48 hours before moisture testing. assuming it’s dry and clean tiling can then commence

Given the type of primer and adhesive you have selected there is no room for cutting corners.

 

[Luggsey]

I hope its dry Alan! House has been sealed up tight and is bone dry.
So if I heat the floor and let it cool again what change will that have made?
Do I need to reconsider adhesive brand, is Mapi not a good choice?

 

[Ajax123]

If your screed is going to crack it will do so when you first run the heating. Do you want the tiles to be in place of this happens.

How do you know it to be dry…. You don’t. Floors do funny things especially when fluctuations in temperature occur. You can get cold spots and dew points. Running the heating also eliminates these.

Nothing wrong with Mapei but as I say no room for cutting corners.

 

[Luggsey]

If your screed is going to crack it will do so when you first run the heating. Do you want the tiles to be in place of this happens.

How do you know it to be dry…. You don’t. Floors do funny things especially when fluctuations in temperature occur. You can get cold spots and dew points. Running the heating also eliminates these.

Nothing wrong with Mapei but as I say no room for cutting corners.

OK, I see your point about cracking, I may have to chance this one room then.
I don't suspect any odd differences in the floor, I helped at all stages and insulation and membrane were all 100%. The house is triple glazed with Velfac windows, never seen even a hint of condensation so I hope that will be OK.
Now to find a method of cleaning the floor without water, I ground the utility floor with a grinder and vaccum attachment but what a faff! May look for a broom like a patio weeder steel brush...
Any ideas?

 

[Ajax123]

Simple str sander hire from speedy hire or hss or any decent hire shop. Grinding is too aggressive really. Sand it, vac it