Self levelling pre tiling

[CC45]

Looking for some advice....

 

22mm P5 floor in timber frame.  Laid by a chippy who must have left his level at home that day so the floor has a wee hump in it.  I took as much off with a sander as I dared but still a bit there.  I had laid ditra matting and eufh cables and I was going to compensate for the floor using more/less adhesive under the tiles.  Her in doors called around today and suggested self levelling compound  - seems sensible - as long as I can get it to flow and settle level then it would make tiling easier plus it would protect the eufh cables as I put the adhesive down.  

 

Good / bad idea?

 

If its a good one - what would be a good recommended product to use to self level the floor?

 

Cheers.

[PeterW]

Yep done this. 

 

Make it quite liquid - another half a litre per bag - and make sure the floor is wet too. 

 

I’ve used Mapei but wasn’t overly happy - it doesn’t cover what it says on the bag. Also used Wickes own brand and that was fine too. Make sure it’s the flexible one though..!

[nod]

39 minutes ago, CC45 said:

Looking for some advice....

 

22mm P5 floor in timber frame.  Laid by a chippy who must have left his level at home that day so the floor has a wee hump in it.  I took as much off with a sander as I dared but still a bit there.  I had laid ditra matting and eufh cables and I was going to compensate for the floor using more/less adhesive under the tiles.  Her in doors called around today and suggested self levelling compound  - seems sensible - as long as I can get it to flow and settle level then it would make tiling easier plus it would protect the eufh cables as I put the adhesive down.  

 

Good / bad idea?

 

If its a good one - what would be a good recommended product to use to self level the floor?

 

Cheers.

You shouldn’t  use self leveller on top of crack matting It sort of defeats the object 

[Nickfromwales]

There are very few flexible self levellers around, and if you try this I almost guarantee you'll end up with a floor that has build up, but is not as level as you'd think it'll end up as. A proper 2-part self leveller is a dream to work with, but AFAIK there are only water based 'builders screed' type levellers available which just dont flow anywhere near as well as you'll need. You will find the high points just get a little higher, which is the opposite of what you want. 

If it were me, I'd identify the high points with a 6' level, and note the bad ( low ) bits. I'd then mix up some tile adhesive and use that to fill the dips making sure to add nothing to the high points. Use a straight edge and level the adhesive off flush to the high points but not above them. Dont worry about the UTH wire, as long as your not wearing stilettos you'll not hurt it. Then apply the SL, mixed ( and added to as I say below ).

 

3 minutes ago, PeterW said:

and make sure the floor is wet too

Ditramat is down and UTH wire too !

 

If you want to use a flexible SL then Ultra is a product I'd recommend as I've used a LOT of their gear over the last 10+ years without a single issue. I'd recommend spraying a dilute solution of Ultra flexible primer / water with a Hozelock bottle immediately prior to laying the SL, and I'd also mix exactly the quantity of water they state on the bag. Once thoroughly mixed chuck a half pint of the mixed primer solution into the SL and then mix it one last time. Get the SL down quickly and thats the best you'll get without hand finishing / trowelling the adhesive as per my first suggestion. 

Make 1000% sure the UTH wire is fixed down and every loop end taped to the floor prior to laying. If you level 4mm and the wire floats up you'll be using the same amount all over again to lay the tiles so will end up 8mm total. Expensive and a waste of time then. Make sure the perimeter is sealed up so no SL can dissaperr down any rabbit holes, as thats a real PITA when you mix up 6 bags but only 2 stay in the room. Caulk or exp foam are your friend there.   

[Nickfromwales]

5 minutes ago, nod said:

You shouldn’t  use self leveller on top of crack matting It sort of defeats the object 

Hence why I use adhesive and drag / spot fill according to the dips. 

Ditra doesn't level though, so there is merit in its ( the SL ) use if its bad. Just how bad it can be over new Weyroc remains to be discussed  

[CC45]

Thanks all, You've convinced me not to use the SL and I think I'm going to use Nicks trick.  Appreciate the input - the hardest bit about self building is that there's no one to mull options over with.  Must remember to take my stilettos off tonight......

[Nickfromwales]

Just make sure the UTH wires are stuck down religiously, then you can use a mix of TA and a rubber grout float to fill in the voids between the wires. That will massively reduce the amount of goo you have to mix whilst laying. The wires are typically ~3-4mm so thats a lot of volume removed before you start laying. It'll also allow you to realise and fill in the areas outside the heated area, plus any untreated ares like under the WC etc, and to fill those up prior to tiling too. Drag the whole floor and use the float to smooth the TA just flush with the wire and that'll also ensure full contact between the wire and the TA, so no chances of hot-spots where the wire is not in contact with any TA  

[CC45]

Good idea - cheers Nick.

[OldSpot]

On 20/08/2018 at 00:01, Nickfromwales said:

There are very few flexible self levellers around, and if you try this I almost guarantee you'll end up with a floor that has build up, but is not as level as you'd think it'll end up as. A proper 2-part self leveller is a dream to work with, but AFAIK there are only water based 'builders screed' type levellers available which just dont flow anywhere near as well as you'll need. You will find the high points just get a little higher, which is the opposite of what you want. 

If it were me, I'd identify the high points with a 6' level, and note the bad ( low ) bits. I'd then mix up some tile adhesive and use that to fill the dips making sure to add nothing to the high points. Use a straight edge and level the adhesive off flush to the high points but not above them. Dont worry about the UTH wire, as long as your not wearing stilettos you'll not hurt it. Then apply the SL, mixed ( and added to as I say below ).

 

Ditramat is down and UTH wire too !

 

If you want to use a flexible SL then Ultra is a product I'd recommend as I've used a LOT of their gear over the last 10+ years without a single issue. I'd recommend spraying a dilute solution of Ultra flexible primer / water with a Hozelock bottle immediately prior to laying the SL, and I'd also mix exactly the quantity of water they state on the bag. Once thoroughly mixed chuck a half pint of the mixed primer solution into the SL and then mix it one last time. Get the SL down quickly and thats the best you'll get without hand finishing / trowelling the adhesive as per my first suggestion. 

Make 1000% sure the UTH wire is fixed down and every loop end taped to the floor prior to laying. If you level 4mm and the wire floats up you'll be using the same amount all over again to lay the tiles so will end up 8mm total. Expensive and a waste of time then. Make sure the perimeter is sealed up so no SL can dissaperr down any rabbit holes, as thats a real PITA when you mix up 6 bags but only 2 stay in the room. Caulk or exp foam are your friend there.   

@Nickfromwales

 

Sorry to resurrect this thread but I've run up against a similar probem where Durabase CI++ is already down. It's a concrete screed with wet UFH embedded.

If I understand you correctly Nick - to level the floor - you work out levels, mix up the adhesive and then trowel/straight edge it level to the high point(s)?

After that, do you need to leave this layer of adhesive to dry and then just going ahead with the tiling as normal or is there anything else to do first to the adhesive layer?

In the first paragraph where you then say "apply the SL, mixed" that's just to cover the UTH wires so wouldn't apply in my case?

 

Also, can anyone clarify why you shouldn't use SL over Durabase CI++?

 

Many thanks for any help!

 

Ps They're stone 900 x 600 so putting them down and then taking them up again isn't simple!

 

[Nickfromwales]

No need for apologies lol.

SLC isn’t typically ‘flexible’, so not normally put over decoupling membranes. If the membrane is down, you could use a “renovation screed’” which is flexible as it’s fibre-impregnated. You’d lay a thicker mix of this vs allow it to self-level if graduating the floor, or leave it ‘runny’ if filling in dips / raising a larger area. You’ll see the recommended water : product ratio on the packaging, so just dial that back 5% if you don’t want it to run away too far from the target area.

If only needing to make up 3-5mm I’d just get them to do that with tile adhesive as they’re laying tbh, 5mm+ then got to renovation screed over membrane.

How much area needs ‘correcting’?

[OldSpot]

Thanks Nick,

 

I reckon it's 8 or so sqms, part of which is >5mm.

Noting your previous comments on 2 part SLC, I can source Arditex NA or Mapei Latexplan locally so I wondered about using that?

According to Ardex you can use Arditex NA to fill in Ditra prior to tiling, although I've got Durabase CI++.

 

Thoughts?

 

KRgds.

[OldSpot]

Or Mapei 3240 seems to reasonably easy to source too.