Kitchen floor, underfloor heating, screed and DPM

[qwertyking]

Hi All,

I am soon to 're do' my kitchen floor and wanted to run a few things by you.

My kitchen will be having damp proof work done to it soon and will have tanking at the bottom. The kitchen floor has been dug up and it appears as though we have hot soil/screed (doesn't look as though there is any concrete any more.

My plan is to lay a DPM on the concrete which will join with the tanking to form a seal. Insulation boards will then go on the DPM, followed by 2 inches of screed, then electric underfloor heating and finally slate tiles.

e.g.

Tiles
---
Underfloor Heating
---
Screed 2 inches
---
Insulation
---
DPM
---
Concrete - 4 inches


Does this sound ok? Is it ok to lay the DPM on the concrete with insulation boards on top?
I can only raise the floor by approx 6/7inches due to head room.

Would it be better to lay the concrete first then the DPM? Can I put insulation boards on DPM?

Thanks all

 

[Ajax123]

What type of screed is it going to be?

 

[qwertyking]

What type of screed is it going to be?

Bog standard 4:1. Do you recommend something else?

Thanks

 

[Ajax123]

Not necessarily. You could use anhydrite screed at that depth without too much of a problem but if you use 1:4 sand cement you are well below the minimum requirements for the material so if you don't do things perfectly you could have some problems with cracking and curling at that depth. The screed should be minimum 65mm (more commonly 75mm with underfloor heating) if sand cement. Anhydrite will go down on underfloor heating at 45mm so 50mm is fine. It can be much better with underfloor heating but can open its own set of issues when tiling. These are easily dealt with but you would need to know a bit about them to make it work properly.

 

[qwertyking]

Thanks Ajax. I've done a quick read on Anhydrite Screed and that stuff looks pretty good. But it probably isn't suitable for me as I have a fairly damp kitchen. So 75mm of sand cement screed it is. (The underfloor heating will be of the electrical type which in effect will be bonded between the screen and tiles by the adhesive.

Any thoughts on having insulation boards below the screed?

Thanks

 

[spooner68]

I've seen a lot of heavy cracking in 4:1 sand cement screeds which have caused grout or tile cracking above. Very difficult to fix if cable UFH is under the tiles and the mat is laid staright on the screed. Insulation boards under the mat and SLC on top before tiling should work as a de-coupling layer and reduce the potential problem whilst improving the efficiency of the UFH mat.

 

[Ajax123]

I've seen a lot of heavy cracking in 4:1 sand cement screeds which have caused grout or tile cracking above. Very difficult to fix if cable UFH is under the tiles and the mat is laid staright on the screed. Insulation boards under the mat and SLC on top before tiling should work as a de-coupling layer and reduce the potential problem whilst improving the efficiency of the UFH mat.

I just typed almost the same as that and my post has disappeared????? must be going senile or something. The other issue with sticking the mat straight to the screed is that the screed will act as a heat sink and will take ages to heat up and will cost a fortune to run. Insulate the top of the screed as well as the bottom. You can reduce the depth of the insulation underneath by the depth of that on top.

 

[spooner68]

Yeah yeah, just copy me why don't you Ajax

Insulation on top of DPC, screed, Marmox (or similar), UFH, SLC, RSFA, Tiles, QED

 

[Ajax123]

Yeah yeah, just copy me why don't you Ajax

Insulation on top of DPC, screed, Marmox (or similar), UFH, SLC, RSFA, Tiles, QED

immitation is the best form of flattery

 

[qwertyking]

Haha. Is there an echo. Brilliant advice guys - Insulation on top of DPC, screed, Marmox (or similar), UFH, SLC, RSFA and then tiles.

Thanks. Very much appreciate it... will stick up some pictures when I get round to it!

Have a lovely evening...

 

[spooner68]

Aok ttfn