Damp cement base limestone and UFH, DPM, Ditra questions - TilersForums.com

[1960bus]

Hi,

I'm new to the board and I wasn't sure where to post my questions as they seem to cover a few forums.

I have a tiler coming to lay some 825x550x20 Mandarin Taj Grey Limestone tiles but we have a problem with one of the rooms the tiles are going to be laid in. The room has a damp floor of original flagstone covered with a sand cement screed and no dpc.

To complicate things we also have some Screwfix electric underfloor heating to go under the tiles. I don't want to try and save money and get the preparation on this wrong and have 20m2 lift or crack.


We can't afford to increase the floor hieght anymore than we already are doing so...

I have been recommended to use:
grout ardex dpm
ardex 82 primer
ardex 7001 adhesive white or grey
ardex mg grout

Should I be using Ditra matting as well? Or could I use the Ditra on top of the damp floor and not bother with the DPC? Should the UFH go on top of the Ditra or underneath?

Thanks,

 

[basshunter]

Hi,welcome etc

Has the s+c screed been laid ontop of the flags recently?if so,why?... confused

 

[White Room]

And with no membrane, flag stones where normally laid on earth.

How old is your property

 

[1960bus]

The screed is about 10mm on top of the flagstone. (The flagstones were laid in earth.) It was laid recently (4 weeks ago) by a builder to level the surface before we realised there was a damp issue.

 

[White Room]

The 10mm screed will be no use at all, there's a good chance it will break up and cause more problems.

What is on the the other floors

 

[1960bus]

The flagstone and screed is on 5m2 of the area the other 15m2 is a 20 year old concrete slab (200mm deep I would guess) that I assume has a dpm beneath as it doesn't appear to be damp. The 10mm screed must have had some additive in it as it was black drying to grey (latex?) the damp bits remain black.

 

[White Room]

Some photos would be handy, the screed could have a heavy cement mix which make it appear very dark

 

[Time's Ran Out]

If its a seperate room you could have lifted the flagstones and put a decent screed with damp course down.
A 10mm (1cm) sand and cement screed over flags is asking for problems and is most likely breaking up as we type!
Ardex 7001 is a very good adhesive and excellent for natural products with its fast drying however it is primarily for TIMBER substrates so Ardex S20 in white/grey would be better suited.
Ditra matting as a waterproofing and de coupling product is one of the best I have used and should be used where stress/movement is expected.
The electric ufh can be used above or below the Ditra.
Visit the web sites of all the products you've mentioned for a full explaination.
However you need to sort your sub floor 1st.

Timeless John.

 

[stevee]

hiya mate ,if its only 5m2 ,why dont u take em up ,and as said above start again in this area?

 

[grumpygrouter]

If its a seperate room you could have lifted the flagstones and put a decent screed with damp course down.
A 10mm (1cm) sand and cement screed over flags is asking for problems and is most likely breaking up as we type!
Ardex 7001 is a very good adhesive and excellent for natural products with its fast drying however it is primarily for TIMBER substrates so Ardex S20 in white/grey would be better suited.
Ditra matting as a waterproofing and de coupling product is one of the best I have used and should be used where stress/movement is expected.
The electric ufh can be used above or below the Ditra.
Visit the web sites of all the products you've mentioned for a full explaination.
However you need to sort your sub floor 1st.

Timeless John.

Ardex have recently reformulated and reclassified 7001 as a general purpose adhesive IDEAL for timber substrates but can now be used on other surfaces too.

It gives surface prep info in their data sheet.

broken link removed