Hi all,
This is my first time on here & boy do I have a doozy of a problem.
I've purchased electric under floor heating & the insulation sheets (not tilebacker boards, cost being the reason). The first thing that happened is that the adhesive supplied to me did not bond the sheets to the subfloor.
The floor is unsealed and the adhesive was for porous floors. Any ideas what I can use instead ?
Also I would love to hear some positive feedback about tiling on these insulation sheets. At the end of the day, they are just compressed foam, so there is still some movement (compression) in them. Has anybody used these successfully ? Thanks to all in advance.

Yes if its the dense foam used to use X7 on them years ago no probs with them:Pete

I usually stick them down with Ardex X7R or Mapei Keraquick, lay the UFH, SLC with Arditex NA or Mapei Fibreplan, then tile with X7R or Keraquick (subject to the type of tiles being fixed) .

Thanks pjc & Captain slow. I'm just relieved to hear that someone has tiled this way. I am definately going to use flex SLC. Thanks again.

Just a tip......after you have laid the insulation board down.....lay some card or ply over the top. This will prevent you leaving footprints all over it and scuffing it up.

Hi lads,
I poured the Arditex latex SLC 2 days ago. Everything looked good until I got home today. Cracks have appeared in the SLC. I'm worried that it hasn't bonded with the insulation. Do you think it would be still okay to tile over this ? Or do I tear it up ?

First off, tearing it up will probably render your UFH etc, un-useable (bad times). As you opted for insulation boards based upon cost, we need a bit more info please.....

Can you post any pics of the cracks?
How thick did you lay the SLC?
Can you provide more info regards the mixing and setting of the slc, please?
How did you fix the UFH (loads of tape or spray glue etc.)?

Originally Posted by Captain Slow

First off, tearing it up will probably render your UFH etc, un-useable (bad times). As you opted for insulation boards based upon cost, we need a bit more info please.....

Can you post any pics of the cracks?
How thick did you lay the SLC?
Can you provide more info regards the mixing and setting of the slc, please?
How did you fix the UFH (loads of tape or spray glue etc.)?

that sounds like a damned good idea Daryl, have you tried it, and does it work ok?

Originally Posted by doug boardley

that sounds like a damned good idea Daryl, have you tried it, and does it work ok?

Got the tip from Aaron, after he slated me for using silver tape. Yeah it works brill, on plywood, insulation boards and sand cement.....give it a go .

will do mate, I use spray glue for all sorts of little jobs, never thought of sticking ufh down with it tho'

Sorry I couldn't reply any sooner.
The SLC is 4-5mm thick.
I fixed the cable using tape. After the SLC was poured there are some parts of the wire sitting up close to the surface.
Rgds the mixing and setting : The Arditex RS plus powder was mixed with the RS plus latex and poured directly on to the UFH and isulation foam.
On closer inspection this morning the SLC is definately lifting in places.
What is confusing me more than anything is that the hallway is fine, with only some very minor hairline cracks.
Could the cracks be down to heat (quicker drying time) ?
Is there anything I can do to stabalise the SLC before laying the tiles ?

hi could be a couple of probs to much tape (slc cant bond ) spray on ah is good in moderation hot melt glue gun is better. has the slc dried all the same colour also if its loose it has to come up be carful of ufh not to damage

Originally Posted by doug boardley

will do mate, I use spray glue for all sorts of little jobs, never thought of sticking ufh down with it tho'

Hi Doug, get yourself a glue gun, sticks far quicker than spray glue, I use it for battons if the tiles are heavy and for ufh, I use spray glue for mosaics and get them smack on level and straight

hi dont like the look of the second pic is it yellowish in color also whats your substrait looks like it hasnt bonded i would recomend lifting the lot sorry

The SLC has discolouration in some areas.
The substrate is a compressed foam (insulation sheet) from Warmsoles.
Will it be possible to up the SLC without damaging the UFH ? (I bloody hope so).

I don't think the slc was suitable for installation over that type of board......

1: Is the board the type that is soley poly core and no cement facing to it.

2: I also don't see any expansion at the edges to the wall.?

Hi dave,
The boards have no cement facing.
What type of SLC do you think would work ?
Not sure what you mean about expansion edges ?

Are they just a dense foam

Did you prime the boards...?


By expansion i mean a perimeter gap around the external edges of the floor.

They are a compressed foam.
They were not primed, the vendor (Warmsoles) gave no instructions about priming.
I get the expansion edges, but never knew they were necessary.
Are they a must ?

Originally Posted by countryboy

They are a compressed foam.
They were not primed, the vendor (Warmsoles) gave no instructions about priming.
I get the expansion edges, but never knew they were necessary.
Are they a must ?

You need to check the Arditex bag, but from memory I think it does advise that the substrate should be primed prior to laying the slc. As well as sealing, this prevents the slc from curing too fast which can, obviously, cause shrinkage and cracking . I'll be using Arditex NA over thermo boards tomorrow, so will check the specs and can advise tomorrow evening, if you like??

Thanks Captain Slow. Any advice at all is very welcome right now.
I managed to find one of the Arditex bags & have attached a photo.
It does mention about priming. I guess the foam would be porous so that could be where the problem lies, too much suction and therefore cracking.
What I really need to know now is : Is there any solution/remedy ?
Or will I have to take up the SLC and pray to God I don't damage the UFH.
Any advice at all is most welcome.
Also attached is a photo of some of the discolouration & cracking together.

hi looking at photos looks like you may have used too much water when mixing causing it to go yellow and lift check directions on bag norm is between 4.2 and 5 litres per 20 kg bag hope this helpes priming also helpes

Howdy lads, Ive cut my losses and pulled it all up. Thankfullly the UFH wire came away from the SLC undamaged. At least using the loose cable had some advantage. If I had used the UFH mats I would have been screwed. The reason for the cracking was the insulation sheets had come away from the subfloor.
Right now I'm down the cost of the insulation and the SLC.
Next step is to prime the concrete subfloor and re-lay the UFH. From there it's just more SLC.
A serious thanks to all who have tried to help. I've definately learned my lesson.
My word of advice to you is never to use those insulation sheets and pay that bit extra to get the tilebacker boards (cement facing).

Just a quick question..i know it's too late now...

You used arditex slc...Now i thought Arditex was a 2 part SLC and you do not use water..just latex liquid and the powder...

Can you confirm if it was a 2 part mix and maybe you were not sold the right package..?

Originally Posted by countryboy

......The Arditex RS plus powder was mixed with the RS plus latex and poured directly on to the UFH and isulation foam.
......

It looks as though the slc was sold and mixed correctly Dave. I'd hazard a guess that the cracks were due to the insulation boards not being stuck to the sub-floor. Too much movement / flex??

didn't see that.......so i wonder why he has a change in slc colour...????

No worries all pulled up now..

Those cracks look like the SLC shrunk and curled. on unprimed foam boards I guess would have dried very quickly - that would cause both phenomena

the color is due to too much liquid in mix making it to wet normally

I can confirm the 2 part mix of powder & latex (not water).
2 possiblilties/reasons for cracks : 1 = foam not bonded to floor
2 = foam not primed for the SLC.
Ah well. Life goes on.