Help needed underfloor heating on concrete sub floor laying stone flags

[Sars]

Hi,

I have a stone cottage and am having sandstone flooring on the ground floor with underfloor heating due to the stone being so cold underfoot. I have ordered 23mm thickness calibrated sandstone and would like UFH. The subfloor is concrete and is mostly level.

I have read up and would like to fit the UFH myself but then get my stone masons to lay the stone on top. They have said they will be using a cement type mortar to lay the stone the same as outside but I have read that due to UFH we should be using the heat proof stuff.

I know the UFH is costly so I am trying to keep costs down where possible.

My questions are:

Is the insulation board necessary ?

If we use the special heat proof self level on top of the UFH matts can we then lay the stone using concrete mortar. The difference in price is phenomenal. To reiterate we are not using stone tiles we are using 23mm calibrated sandstone so obviously thicker.

We are just looking to basically take the chill out of the stone, not using the UFH as a primary source of heat as we have wood burner and radiator in the room. Plus the living room is only 22m2 of stone being put down anyway.

Any help please as don't want to get into something before we realise its too much work and cost.

 

[Flintstone]

Insulation is a must, or you will be paying to heat the concrete floor! I would advise that they are stuck down with tile adhesive as it’s much stronger and more flexible than sand and cement. Most decent levelling compounds are suitable over underfloor heating

 

[Sars]

Thank you very much for your reply.

Ok so Im sold on the boards makes efficient sense.

So are you saying that we need heat proof tile adhesive the fibre or latex type to lay the stone on top of the self level compound which will of course be the suitable product for UFH?

Then would you be able to grout with normal cement?

 

[Flintstone]

Any s1 rated adhesive will be fine to stick the tiles down. All the main manufacturers make this, its standard flexible adhesive available in slow set or rapid set.

 

[Dumbo]

To be honest as @Localtiler says flexible adhesive , flexible grout and flexible levelling compound . Also I've seen stone masons laying floors and I would be using a tiler .

 

[One Day]

Sand and cement on a heated floor will very likely fail unless they modify the mix with a polymer. They'll also likely spot-fix with blobs, if they're inclined to suggest s&c on a heated floor!
It's calibrated stone so a flexible s1 tile adhesive would be better.
Ditto stone masons and laying floors.
Stone masons are not tilers, and tilers are not stone masons.

 

[Flintstone]

23mm thickness is deffinately within a decent tilers capabilities

 

[Sars]

Thanks so much.

So basically the cost of fitting the ufh is actually turning out to be a lot more than what we anticipated with everything on top such as the adhesive, self level and insulation boards!

 

[Dumbo]

Just to clear something up . Self levelling doesn't self level so I would get someone that knows what they are doing with it .

 

[Sars]

Impish thanks for your input.

The stone masons we use have been doing stone work on our property re pointing with lime etc. Their workmanship is fantastic and they have done a lot of heritage and national trust work. When we told them we were getting a sandstone floor they offered to do it. When I mentioned we would like UFH they didn't seem to think it was necessary as we have GCH and a wood burner.

They have never worked on UFH and so this is what brings me here. It made sense to use them as we are carrying on the stone flooring to the hearth and to top other stone work that they have already worked on with lime mortar.

I will ask them if they can use a polymer to the mix and if not then I will go for a tiler who is more accustomed to the materials required for UFH.

I concur with the stonemason not a tiler, tiler not a stonemason!

I've got a 46m2 space to lay but only 21m2 of UFH just working the costs out.

 

[Sars]

So why is this stuff called self level?

I've heard this stuff can be awkward to use. I think I will need a pro for that part for sure. Might get a quote for the whole job at this rate

 

[Flintstone]

The stone masons aren’t going to be able to fit the insulation, or the heat mat, or do the levelling, or be used to sticking there stones down with a solid thin bed of tile adhesive. Get a tiler in who can do all of these things for you. I know you probably have a good relationship with the stone masons. I’m sure they will understand

 

[Sars]

Well I was going to attempt to doing it myself but the more I look into it the more complex it's getting.
Thanks

 

[Flintstone]

There’s a thread on here by a chap called mp3wizaed called something like ‘how to tile a floor’. Check out his endeavours 😱

 

[Dumbo]

So why is this stuff called self level?

I've heard this stuff can be awkward to use. I think I will need a pro for that part for sure. Might get a quote for the whole job at this rate

To my mind there should be some sort of trade description issue

 

[Flintstone]

It does self level, it’s not water so it’s not gonna perform miracles but if you dig a hole and pour self leveller in, it will set level !

 

[Sars]

Wow localtiler I just read the whole thread you suggested.

Thank you for saving me hundreds if not thousands of pounds. I know of people who have apparently pulled it off but I haven't seen their finished ressult in person and experienced ufh in a previous house that a diyer completed and albeit 6 years later it had to be ripped up and redone.

Mp3wizard was very brave and is a lesson for everyone. Admire his efforts and everyones help on here but i will follow your advice and I will not be attempting this myself, it's an extreme gamble and I'm not into that at the area I am looking to cover.

So next job for me is to get some quotes off the pros and decide whether its worth doing or just wear slippers!!

I am on the Wirral if any of you are interested in providing a quote let me know and we cam discuss over the phone.