Advice sought on new screed, uncoupling membranes etc

[mpphillips]

Hi everyone,

This is my first post and I'm seeking opinions regarding the formation of the gradient in a wetroom, uncoupling membranes and UFH so it probably falls between this forum and the UFH one. Hopefully I'm in the right place!

I guess some background would help: I'm planning the total refurb. of our bathroom which is downstairs at the back with a concrete floor (typical late Victorian end of terrace). I've got a builder coming-in to move the doorway and relocate the soil pipe, so we're going back to bare brick and taking up the existing screed down to the subfloor. We're not convinced that there's a reliable DPM or insulation below the screed so they'll both be installed before laying a new screed. My background is Engineering, so other than the heavy building work, I'm planning to do most of the work myself.

We want to go down the wetroom approach. The room has primary (central) heating but we want to install electric under-tile heating and I want to minimise warm-up time - with the implication that I need insulation immediately beneath the heating cable. I've got a bit stuck between to different approaches. Should I (i) Form gradients when laying the screed, use an uncoupling membrane (probably Dura-CI) then lay loose wire heating, self levelling compound and the tiles? or (ii) Lay a level screed, fit a pre-formed tray and butt-up tile backer boards to it, then the Dura-CI, heating, SLC etc?

I'm drawn to the first approach given that a new screed (sand and cement) will be going down and it'll save on materials and time, but will the absence of tile backer boards mean that too much heat goes down into the screed? Or does Dura-CI act as an effective thermal insulator and reflect the heat upwards into the tiles?

Also, while I'm here, a couple of other things:

If I opt to heat the floor at 200 W/m2 do I significantly increase the risk of cracking over (say) 150 W/m2? and,

When laying SLC, do you tackle the gradients (with a stiffer mix) first, let it dry and then do the rest of the floor? Or lay/pour both sections one straight after the other?

Thanks in advance
Malcolm

 

[grumpygrouter]

You really need the uncoupling membrane above the UFH to isolate the tiles from the thermal load if you are going this route and I would definately go down the thermal backerboard route underneath for efficiency purposes.

As for the screed questions, I am not experienced enough to answer those, someone else will answer though, I am sure.

 

[DHTiling]

Another option is to use a loose cable system built into the screed .... A few manufacturers are offering this system now...

This one supplier who you will get great prices from and free advice on the installation..and will be a better primary heat source..

In-Screed Underfloor Heating | Electric | Uheat

then you can form your falls in the drain area and still use durabase ci for tanking...

 

[wetdec]

The better faster warming heat saving direction would be a 150w wire over a thermal board. Putting a 200w cable in the screed will mean heating the screed to temperature over jabolite so your heating minimum 50mm screed before the tiles imo.



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[wetdec]

You really need the uncoupling membrane above the UFH to isolate the tiles from the thermal load if you are going this route and I would definately go down the thermal backerboard route underneath for efficiency purposes.

As for the screed questions, I am not experienced enough to answer those, someone else will answer though, I am sure.

Dura-CI is there to protect from the screed deflection m8 so if used would go under the ufh cable.

Same on wood..........

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[mpphillips]

Thanks for the (very fast) replies so far.

Dave: I've looked at in-screed cable, but as Wetdecs says it'd heat-up the entire 50mm (or so) of screed plus the tiles. I'm not keen on dumping several kW of heat into the screed for a few hours just to warm up the tiles in the morning (and possibly the evening).

I found a wetroom site somewhere (can't find the URL now) which stated something along the lines of product xxxx "is effectively a tile-backer board on a roll". It didn't refer to dura-ci but it was the same type of product. Does that some feasible? Or is it safe to say that if you want fast warm-up times for the tiles, you need a thermal backerboard - with the implication that you should lay a flat screed and form the gradients using a former?

Cheers
Malcolm

 

[wetdec]

email me the details and I take a look at the product for you if you need some help...............

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