25mm sandstone slabs laid onto 50mm of jablite insulation - TilersForums.com

[Matthew77]

Hi all

Am I right to think that this is complete madness. I've been told about a job today that I might have as potential work.

Its a conservatory extension with 50mm of jablite type polystyrene insulation on the floor & then some electric underfloor heating matting laid on top of that I'm under the impression that they want me to lay 25mm sandstone slabs using a flexi addy onto that. this sounds insane to me am I missing something here or what? :yikes:

Wouldn't insulated cement board laid onto floor with electric underfloor heating matting on that then self levelled & stone laid onto the self levelling with a flexi adhesive be the way to go with this? Hopefully the electric underfloor heating is a whopper to heat all that stone?

 

[Rob Z]

Hi Matt, I'm not familiar with that brand of insulation. Is it like Wedi board? If so, maybe it is designed to have tile set on it?

As for the UFH and heating the thick stone above it...the mats we use here are all 12-15 watts/square foot. I have installed UFH on slabs and then use SLC and thick tile and stone on top and never had problems with the floor heating up. Once it reaced equilibirum, it is fine.

With that insulation below the stone on your job, I asume your UFH will do fine with your stone. Do you know the watts/square meter for your UFH?

 

[Matthew77]

Hi Matt, I'm not familiar with that brand of insulation. Is it like Wedi board? If so, maybe it is designed to have tile set on it?

Its made from polystyrene I believe you know the little white bubbles like you used to get in packaging for electrical goods like televisions. My concern would be the movement in the polystyrene insulation. I know that this is often used for floating floors & Ufh with the water pipes with a screed laid on top but, I'm pretty sure it'd move about too much unless quite a thick screed was laid on top? I suppose that would heat up, but wouldn't some thing like DUKKA or WEDI board be a much simpler alternative?

Anyone know what the minimum requirements for screed depth would usually be for screed on top of jablite insulation?

Thanks

 

[Rob Z]

Matt, that helps...we have a backer board panel here in the US that is made of the same stuff, but it is marked "for wall use only". Sounds like your instincts on this one might be correct.

 

[Matthew77]

Matt, that helps...we have a backer board panel here in the US that is made of the same stuff, but it is marked "for wall use only". Sounds like your instincts on this one might be correct.

according to the jablite website the screed should be at least 65mm thick for domestic jobs. then adhesive & 25mm sandstone slabs. That's quite a bit of materials to heat up. Would that not take quite a while to heat up with an electric mat or is that not really a problem?

 

[Rob Z]

Matt, a screed that thick has its own strength and spreads the load evenly over the foam. It sounds like the same method used here in the Northern US and Canada. As for heating all that material up...I think once it gets to an equilibrium it works. That mass of masonry is a heat sink and with the insulating panels below to prevent heat loss, it all comes back up toward the living space. This is the way it has been expained to me.

 

[CBTC]

You have to screed it yes. The 65 mm would be a min I would say.
Whoever suggested the first method hasnt got all their bricks lined up in a row.
The use of electric ufh is'nt going to be the most effective or economic in this situation, no. It will have to be one of the higher rated types in the first place.
Hope they havent planned it missing out the screed lift!!

 

[Perry]

Is it the dence foam ?

 

[Matthew77]

You have to screed it yes. The 65 mm would be a min I would say.
Whoever suggested the first method hasnt got all their bricks lined up in a row.
The use of electric ufh is'nt going to be the most effective or economic in this situation, no. It will have to be one of the higher rated types in the first place.
Hope they havent planned it missing out the screed lift!!

Higher rated as in 200W/m2 or higher?

I wouldn't be suprised if they intended on putting a small screed on top to keep the height down, I'll see in a few weeks when its all ready to tile.

Most of these systems are supplied with there own insulation board I'm guessing so that they work more effectivly, as I understand they don't wack out a great deal of heat.

 

[Matthew77]

Is it the dence foam ?

I've no idea, I spoke to a builder that had been on site & he asked if I was laying the stone, then said they had put down jablite insulation, I then asked if it was hot water UFH & he said no its the electric matting...we both looked puzzeled.
:dizzy2: