Hello all, I'm just about to lay my first Devimat UFH. The substrates are 18mm floor boards, 12mm ply (all screwed down at 300mm) & 10mm Marmox insulation boards on bathroom floor.

The floor is completely flat & level. Do I still need to use a slc, as the devi instructions say tile straight over with a flexible adhesive.

Reading from other posts, I gather its to protect the wire from damage.

I'm planning to use Mapei Fibreplan, and do I also use the slc over the wet dec in the wet area? I'm guessing not as it may mess up the gradient?
regards

I always use slc over ufh as it does protect the cables, and gives you a nice surface for tiling onto. On the shower deck i would spread a flexible adhesive over the cables,and smooth it off with a plastering trowel, carefully though so you dont damage the ufh.

Hello ap

Definately better to use latex based SLC on top of the UFH Cables - cover them to a flat surface - important to use SLC with latex / highly flexible alernative / mapei fibre plan might ok you'll have to check this out with Mapei or most of the boys and girls on here that use Mapei.

As for the Wet area - deck etc - never lay UFH cable on wet room decks and never apply SLC or anything else for that matter - subject to the type of deck you have. If its a cementous board deck with pre-manufactured fall, don't ever, and the only thing I would consider on a 'solid plastic deck' would be a thin brushed-on sbr primer coat, although this should not be necessary - These decks are all designed to accept tiles / flexible adhesive directly

Thank you for the advice guys, I will use the slc to cover the cable.

Richard, I'm using the novellini Linear Wet dec with a 2 way fall & was hoping to install the UHF onto the deck. The instructions advice placing any UFH atleast 20cm away from the trap to prevent water in the trap drying out.

The tray is white looks cementious and has a preformed 2 way gradient.

regards

You will be ok putting ufh on the deck, as long as you are putting a membrain over it

Apart from above mentioned the other main reason to self level over UFH cables & mats is to avoid creating hot spots.
Hot spots occur when there are air pockets in the adhesive,when used directly over cable or mat.
The cable should be ennitrely covered ( encased )! This is very difficult to do unless self levelled. The hot spots are areas where cable could malfunction or over heat.

Originally Posted by poynton phil

You will be ok putting ufh on the deck, as long as you are putting a membrain over it

Hi Phil,

I am installing the tilesafe membrane, but that will be installed first, and then UFH on top of it, as shown in Impey installation videos.

regards

I dont know much about the tilesafe membrain as i'v ever used it, i have heard that its a ***** to install, if your not used to it though. Me personally would not have the uhf on the deck if not covered with a membrain.

Originally Posted by poynton phil

I dont know much about the tilesafe membrain as i'v ever used it, i have heard that its a ***** to install, if your not used to it though. Me personally would not have the uhf on the deck if not covered with a membrain.

Well, i've bought it now so got no choice but to go with it! I'm sure I'LL be alright as long as I work methodically & not rush the job

Thanks for your input guys, much appreciated.

Tilesafe membrabe is ok to fit if you follow instructions.
Make sure you do not remove protective film prior to tiling,it is so sticky you will get stuck to it. It will also attract & stick every bit of dust & rubbish that is around.
Also, very important to press and roll out as instructed, otherwise you will get air bubbles in the membrane. These can be an absolute **** especially if fixing mosaic tiles.
Make sure you seal all membrane joints with supplied sealant, do not use silicone as this destroys the membrane & invalidates any warranty.
Use supplied primer as directed prior to fixing, all areas should be clean & dry prior to priming. Primer should have been allowed to dry out prior to fixing membrane.

Hi ap

Well some members say its ok to install UFH on the deck and I still say not - pick the bones out of that if u will. Personally I would never do it, apart from the fact that I cannot see a technical / comfort reason to do it and you are spending money on an extra area of matt apart from the increase worry of interferring with the falls - ie from outer to inner on a Lux Cementous Deck its 50mm - 35mm ie the fall is only 15mmm over say 900mm on the largest deck, enough to drain OK but not much to play with if your adding other components before tiling.

As regards the novellini Linear Wet - I cannot comment as its not a system I use, but clearly the manfacturers instructions are gospel.

Good luck with it - perhaps post a couple of 'in process ' pics if you can - I would like to see how this deck system compares

Hi Richard, Thank you for the reply. If I decide not to fit it under the dec
I will end up with extra UFH cable, as when I bought it, I accounted for the wet dec. The kit may be slightly larger for the room now.
Can I just run the excess red cable along the perimeter of the room, keeping 50mm gap from other wires to prevent overheating?

I will get some pics up of the install as soon I get down to fitting it.
I think this dec is made by Impey (Linear -flo dec) for Novellini, as its resin filled and allows upto 3 traps to be fitted.

Many thanks also to Yorkshire tiler, for the advice & tips on laying tilesafe.

Originally Posted by Richard Edwards

Hello ap

Definately better to use latex based SLC on top of the UFH Cables - cover them to a flat surface - important to use SLC with latex / highly flexible alernative / mapei fibre plan might ok you'll have to check this out with Mapei or most of the boys and girls on here that use Mapei.

As for the Wet area - deck etc - never lay UFH cable on wet room decks and never apply SLC or anything else for that matter - subject to the type of deck you have. If its a cementous board deck with pre-manufactured fall, don't ever, and the only thing I would consider on a 'solid plastic deck' would be a thin brushed-on sbr primer coat, although this should not be necessary - These decks are all designed to accept tiles / flexible adhesive directly

There are UFH cables that are suitable for wet floors.
This is the only instace where I would not self level prior to tiling. Instead I would screed over carefully with a flat trowel, following the fall in all directions. Have done this on numerous types of wet floor without a problem or call back. Ok providing a suitable adhesive is used.

Thanks Yorkshire T, appreciate the photos you've put up, great finish on that job
I checked the specs with Devimat & its totally waterproof including the cold tail. Im gonna be using Mapei keraquick flexible rapid set adhesive for the tiles so it should be fine.

Just a curious question, why isn't it wise to use slc on the decs? Is it because it would not maintain the preformed fall of dec an try & set horizontally?
regards

Originally Posted by ap222

Thanks Yorkshire T, appreciate the photos you've put up, great finish on that job
I checked the specs with Devimat & its totally waterproof including the cold tail. Im gonna be using Mapei keraquick flexible rapid set adhesive for the tiles so it should be fine.

Just a curious question, why isn't it wise to use slc on the decs? Is it because it would not maintain the preformed fall of dec an try & set horizontally?
regards

That is correct

Originally Posted by ap222

Thanks Yorkshire T, appreciate the photos you've put up, great finish on that job
I checked the specs with Devimat & its totally waterproof including the cold tail. Im gonna be using Mapei keraquick flexible rapid set adhesive for the tiles so it should be fine.

Just a curious question, why isn't it wise to use slc on the decs? Is it because it would not maintain the preformed fall of dec an try & set horizontally?
regards

Hello AP

Re Not using SLC on a preformed wet room deck - This is as you have said. SLC wants to run dead level and unless you are very clever with it its not recommended as it will run to the drain and the fall will not be a fall at at all . Why interfere with the fall and gradients of a preformed deck - You buy these things to save you having to create the fall - Some decks are very low in gradients and being out by as little as 10mm can mean it will not work as a free draining shower but will resemble a continous puddle.

Re Excess cable - You could 'loose' the excess cable as you say - running it around the edge of room - ie outside the matt line as long as you do not reduce the 50mm clearance between cables - even cold tails.
The Devimat is in my opinion, the best or one of the best on the market - we always use them if we can.

Re Waterproof cables - suitability in wet rooms . Yes they are and are most suitable for wet rooms - no problems with that. I know YTS Yorkshire Tiling Services has posted an interesting and worthwhile post on how it can be done using flexible addy or a mix etc. I have no issue with that and only last week did a major remedial job on a 'disabled wet room' for a contractor who thought his lads could do it - and they clearly could not, and used the same / similar method as our YTS member. That said, I think that skimming a deck with heating cable under it is not recommended unless you have some experience. - Now, I still cannot see why anyone would want to install UFH on the deck ! It becomes warm the minute the shower is on and retains enough heat to dry it out afterwards.

Hope this gives you the answers you were looking for.

Thank you Richard & YTS for the extremely constructive comments and invaluable advice. Its really goes to show how little I know & how much more I can learn from experienced members like you on this forum

Before I joined, I knew little about tiling methods, substrate prep & so on, its being a great help joining this site.

regards

Originally Posted by Richard Edwards

Hello AP

Re Not using SLC on a preformed wet room deck - This is as you have said. SLC wants to run dead level and unless you are very clever with it its not recommended as it will run to the drain and the fall will not be a fall at at all . Why interfere with the fall and gradients of a preformed deck - You buy these things to save you having to create the fall - Some decks are very low in gradients and being out by as little as 10mm can mean it will not work as a free draining shower but will resemble a continous puddle.

Re Excess cable - You could 'loose' the excess cable as you say - running it around the edge of room - ie outside the matt line as long as you do not reduce the 50mm clearance between cables - even cold tails.
The Devimat is in my opinion, the best or one of the best on the market - we always use them if we can.

Re Waterproof cables - suitability in wet rooms . Yes they are and are most suitable for wet rooms - no problems with that. I know YTS Yorkshire Tiling Services has posted an interesting and worthwhile post on how it can be done using flexible addy or a mix etc. I have no issue with that and only last week did a major remedial job on a 'disabled wet room' for a contractor who thought his lads could do it - and they clearly could not, and used the same / similar method as our YTS member. That said, I think that skimming a deck with heating cable under it is not recommended unless you have some experience. - Now, I still cannot see why anyone would want to install UFH on the deck ! It becomes warm the minute the shower is on and retains enough heat to dry it out afterwards.

Hope this gives you the answers you were looking for.

great post Richard, well explained

I asked Impey Tile safe technical dept this question last week. "can I lay ufh on top of tile safe"? the answer was "no" yet I have read somewhere that you can

Originally Posted by Phil Hobson

I asked Impey Tile safe technical dept this question last week. "can I lay ufh on top of tile safe"? the answer was "no" yet I have read somewhere that you can

I guess it depends which UFH you install. Impey only recommend the Devi 100W, as other more powerful mats may damage the membrane.
When I emailed their technical, they advised me that it can be laid under the tilesafe, so long as you keep the mat 200mm away from the trap, as it could otherwise dry out the water within the trap.

Originally Posted by ap222

I guess it depends which UFH you install. Impey only recommend the Devi 100W, as other more powerful mats may damage the membrane.
When I emailed their technical, they advised me that it can be laid under the tilesafe, so long as you keep the mat 200mm away from the trap, as it could otherwise dry out the water within the trap.

Sorry chaps, my post should have read "it can be laid over the tilesafe" and not "it can be laid under the tilesafe".

Hi guys, need some advice, i have laid ufh mats and covered with Sika latex, i know have discovered i should not have put this compound directly over the mats, rang Sika and they have told me the levelling compound may crack, any advice?

Originally Posted by wooferdog

Hi guys, need some advice, i have laid ufh mats and covered with Sika latex, i know have discovered i should not have put this compound directly over the mats, rang Sika and they have told me the levelling compound may crack, any advice?

Stick to your original thread Wooferdog otherwise you will get dizzy flicking between the 2 for your answers.

Originally Posted by grumpygrouter

Stick to your original thread Wooferdog otherwise you will get dizzy flicking between the 2 for your answers.

Not Sure if its OK to help you with this as Grumpy has put a caution there. Normally we would use Latex based SLC over heating mats so I am puzzled by Sika's Technical advise. It might be that they are being a bit over cautious - not sure. ! I would probably run it up to normal operating temp over a few days [increase by 10 C per 24 hrs as max, ] and allow a day to cool and as long as there are no major cracks and delamination I would tile over.

I have run the heating and no visible cracks so far, just to be over cautious i have laid ditra matting so if in the future it does detioriate the tiles have a chance of staying put or thats the theory.

thanks