Marble Floor

[jimbo]

Hi

Would it ok to lay 600X600 Brushed Marble 12mm thick onto a newly laid Concrete floor with Bal Rapid Set Flexible adhesive ? There is underfloor heating. I realise I would have to wait 6 weeks for the concrete to cure.
Any advice would be appreciated.

 

[Tilerbhoy]

How thick is the concrete floor,it's 1 day per 1mm you need to leave it before you can tile on it

 

[jimbo]

The slab is 4 inch on top of underfloor heating

 

[peteablard]

I'd strongly recommend using ditra too

 

[Peter]

Ditra and white slow set flexible would be the way I'd go about it. You'll be able to tile it ASAP that way too.

 

[DHTiling]

You WILL need to commission the screed before any tiling cam commence and this cannot be done for 21 days after screed is laid.

 

[Concrete guy]

I just don't get the idea of using Ditra matting in these circumstances. I supplied tens of thousands of sq/m of marble and limestone over the years for fits of this nature. Only one used Ditra due to the substrate being a little unstable (and it still failed eventually).

The only upside of Ditra in this circumstance is being able to tile on a green screed. The heating still has to be commissioned beforehand.

The downsides are:-

The Ditra acts as an insulation between the UFH and the marble making the UFH less effective.

Using adhesives with flexible additives technically negates the decoupling properties of Ditra Matting. I had more than one very long conversation with Schluter about this over the years. (unless they've changed their minds I can't see how this aspect could have changed substantially).

If I were tiling this, I'd make sure the screed was dry, 1mm per day is a good guide, but if the ambient temperature is below 5 degrees that could be 1mm per 10 days - there's plenty to consider. Make sure it's dry, make sure the heating is commissioned once it is dry, then fit with a suitable flexible white adhesive and suitable primer. No need to uncouple at all. This is a screed, not a boarded floor.

 

[DHTiling]

Ditra does not act as an insulator.. it helps disperse heat through the channels.. and also new cement based screeds can crack as they cure over the first few months especially with heat.

They can and do shrink or curl..

 

[Peter]

The decoupling is a bit of a minefield at times. Have seen stone laid direct to screeds where it's never split at all, and other times where the floor has cracked all over the show. The heated screeds do have a tendency to crack more than unheated though from what I've seen. With an unheated screed and plenty of correctly applied expansion gaps then I'd have a bit more faith laying direct but perhaps only if the floor was down for a long time.

 

[Concrete guy]

Ditra does not act as an insulator.. it helps disperse heat through the channels.. and also new cement based screeds can crack as they cure over the first few months especially with heat.

They can and do shrink or curl..

My statement was based on the technical conversations I had with Schluter when I was supplying large quantities of stone for commercial fits. Albeit 10 years ago now.

I agree that screeds shrink and curl, that's why they need to be dried and the heating commissioned beforehand.

I realise there are a lot of fans of Ditra matting on here and it certainly has some good uses but I don't feel this is a necessary one.

 

[Diggy]

UFH - Natural stone = decoupling mat , no brainer.

Diggy

 

[jimbo]

The floor is approx. 25m2. I have tiled concrete floors before with underfloor heating with no problem without a decoupling membrane,but only 15m2 max.My original question was if Bal Flexible Adhesive would be ok.

 

[DHTiling]

Yes the adhesive is suitable for a fully cured and commissioned screed.

 

[jimbo]

Thanks for that information.

 

[Concrete guy]

I always preferred Ardex S20W for marble, it releases it's moisture (or more importantly doesn't release it's moisture to avoid water staining) in a different manner more suitable for natural stone, particularly if it's a light marble.

Not particualrly cheap though but suitable for UFH.