Electric mat installation

[1animal1]

Hi

I am in the process of fitting a new En suite out and have recently bought a 2m2 heat mat with digital timer. So far I have chased through the walls, ran the electric feed to a fused spur (3A - it's only 150w rating) and ran conduit to the floor ready for the mats cables. The question I have is around the process and a couple of niggles.

The plan is to use the supplied thermal primer compound to prep the newly laid wooden T&G floor boards
(I have enough for 10m2 so thought i'd use that instead of buying something similar), then use a flexible tile adhesive to lay 10mm insulation boards, filling any gaps with adhesive. I'll then prime the insulation boards with the thermal primer before laying the mat, testing the mat, then screeding over ready for tiling with 10mm 60x60 polished porcelain.

I have asked this on another part of the forum and had 1 answer, but the instructions are a bit vague. The cold/hot feed bulky connection that needs setting in tile adhesive? My plan was to hide this in the lower wall, sunk in tile adhesive then a wall tile on top (I've made a recess of about 30mm) - presume the recommendation to sink in tile adhesive is to spread the heat about. Another forum member suggests cutting into the insulation board and screeding over but the instructions say specifically not to do this due to overheating and premature failure, the insulation board obviously retaining any heat the connection gives off. What do you chaps do?

Second query is around the door trim. I am going to buy a chrome z door trim that can be hammered down (with a lump of wood), to accept 25-30mm given the 10mm board, screed, mat and 10mm tiles. Luckily i have a decent depth carpet on the other side to hide this - are there any other trims worth looking at? I'm conscious that it may look tacky in chrome? or is this standard....I am also wondering what to do when screeding, do i put a piece of wood in place of the door trim to screed up to then remove to fit the door trim once tiled?

Thanks in advance and sorry for all the amateur questions

Tim

 

[Flintstone]

I think it was me who mentioned about the bulky connector. I have used that method for many many installations without a problem, you just need to dig out about 3mm of the insulation board to make the cold tail connector sit at the same height as the rest of the wires, then it ensures that it all gets coated in levelling compound. Putting the connector in the wall risks having an area that's not properly covered somewhere between the floor and the wall. That's my opinion anyway !

 

[Old Mod]

Who's UFH system is this?
I have always sank a small amount of the large cable in to the substrate partly.
You have to, otherwise you're looking at a massively thick layer of slc.
If it's a timber floor, I'll chisel it out, if it's insulation boards I'll cut a channel.
And if you didn't then a small part of the heating cable would have to be left exposed, because of the transition between the two, and that's not right.
I can't see a problem with this, I'd be interested to read their instructions.

 

[jobdone]

As above chanel out the boards for the cold tail and the flexible conduit for the probe. I find it best to always use conduit for the probe as it can then be changed if it fails, I even do this with ditria heat.
Trim the edge of the tile in to the door way then the carpet can be finished into it leaving a neat finish imp.

 

[Dumbo]

Unless I got this wrong most if not all ufh manufacturers state that join between heating cable and cold tail should be encapsulated either in adhesive or levelling compound .

 

[1animal1]

Hi, sorry for the late reply, the brand is Nass boards. I'll try and take photos of the instructions tomorrow. As mentioned above though they state that the connector should be under the tiles, encased in adhesive or screed... With an important note to not just cut out the insulation and cover with tape as it risks overheat. That must be the element I missed.... As it wouldn't be encapsulated in adhesive or screed.

Regards the door, do I just use a piece of wood to replace the trim for now until the jobs complete?

 

[1animal1]

Local, I think it was you that commented mate, on reflection my question is void thank so much for the advice... Same to everyone else who's commented. I've already ran the conduit but have another piece spare that goes to the floor past the void I've carved out. Fingers crossed it all works when powered up! Any thoughts on using the thermal primer to prime the floor boards, it should be OK shouldn't it?

 

[jobdone]

Have you tested the mat ? A simple resistance test at each stage in best
Out of box
Laid out
After covering with slc

 

[1animal1]

I was just going to put the Avo across it, and test the resistance as you say.

I'm still a couple weeks away from installing so it's just a matter of priorities atm.

 

[Old Mod]

I was just going to put the Avo across it,

Now I've not heard that term in a very long time!

 

[1animal1]

I had an old teacher

 

[Old Mod]

I had an old teacher

Haha that'd explain it!

 

[Qwerty]

Yes, channel out boards to accommodate the end of the mat and the transition between cable and mat.

Here are some photos of them channeled in (apologies they were at the edges of the original photo so I had to zoom in) and then self levelled.

 

[1animal1]

That's brilliant, thanks for the pictures. Really helpful....

Is it not a concern regards air pockets forming under the tape holding the cable down?

 

[Dumbo]

Yes it is . But the fact he has taped it in strips it should allow leveling comp to get in .

 

[1animal1]

Problem solved I didn't know how fluid the screed would be.

Thanks again chaps for all the advice

 

[Qwerty]

Yes it is . But the fact he has taped it in strips it should allow leveling comp to get in .

Spot on! I always leave a big enough gap around it to allow the slc to fully encapsulate it hence it being strips holding it down. Means no air pockets

 

[1animal1]

Thanks JCR, much appreciated

 

[1animal1]

Right, I have the boards down, heating mat down and tested and one layer of Mapei screed...trouble is, the screed only partially covers most of the cables after a few have risen about 2mm above. I know i can use adhesive on the porcelain tiles when laying which will obviously remove the risk of cutting the cables - but i am more worried that the job isn't being done properly - the conductive properties of the screed, depth (which is 5-6mm), the fact that i can't apply adhesive to the floor etc.

Question is, with the total thickness in mind,can i get away with applying adhesive to the tiles - or am i an idiot for not chucking another bag of screed down?

 

[Flintstone]

If it's just the odd wire poking up a couple mm just tile as normal but be a bit carefully when trowelling around the wires

 

[1animal1]

That's what I was hoping you'd say! the cold connection is out about 3mm too after reviewing this morning... will this be ok or does it need to be fully encased in the screed

 

[Flintstone]

As long as it's fully encased in screed or adhesive that's fine. 3mm is quite a bit, be careful and be carefull not to rub coating off the wire when trowelling or bedding a tile down

 

[1animal1]

Will do and thanks - I was going to navigate around the wires then back butter the tiles to be safe....

 

[SJPurdy]

Will do and thanks - I was going to navigate around the wires then back butter the tiles to be safe....

be careful by the wires but make sure they are covered by/encased in adhesive, so don't navigate "navigate away from them to far.
back butter all the tiles to ensure a solid bed.

 

[1animal1]

Noted - this is going to more long winded than thought as i've 3 bags of rapid set.... thankfully only 6 600x600 on the floor and 66 600x300 for the walls! reckon i'll get 2 or 3 laid per mix?

 

[Flintstone]

You will probably get 3m2 out of a bag

 

[1animal1]

I'm more worried about the 10 minute lay time

 

[Dumbo]

I'm more worried about the 10 minute lay time

If you can take them back and get some slow set .

 

[1animal1]

Possible if i wasn't a smart a***, buying some Mapei porcelain and stone split bags from Tradepoint @ £16 for 2 (notice how cool i am not shopping at B&Q ).

I've also got a bag of Weber from a bathroom fitter mate - but reckon i'll need some more before the jobs done, i'll get some slow setting next time.

 

[Time's Ran Out]

You spend all that money on tiles then half inch the adhesive!