self leveling cracking

MassiveJim · Sunday at 16:58

Recently poured self leveling on bathroom floor and it is cracking. will I be ok to lay tiles on this or will it need to come up ?

Floor is
18mm plywood
6mm insulated cement board
primed, then lay electric UF heating mat
6mm(ish) of self leveling
at this stage some of the heating elements had come unstuck and risen to the top of the screed.
So i dug out the worts affected areas and secured them to the floor then covered with tile adhesive
then primed again and repoured 3mm of self levelling over the top of the existing

now it is cracking. see pictures below

MassiveJim · Sunday at 18:49

It's no nonsense slc from screwfix says 1 to 10mm.

Plywood was screwed down and the cement boards were screwed down to that as well. Used plenty of screws.

I could hear the floor cracking when I walk on it. Not so much now though.

MassiveJim · Sunday at 22:36

200sols said:
Did you use a layer of tile adhesive between the cement boards and the ply? Usually use a 6mm trowel when fitting hardibackers to wood to take out any unevenness.

No because it was laid on ply I didn't bother. I did do a bit of research and found tradesmen online who said that they never do it and never had any problems.

MassiveJim · Sunday at 22:40

Buffman said:
Is it just hairline cracks? Did you primer before self levelling (2nd time?)

Does it feel loose /hollow?

Most/all internal concrete slabs and/or screeds will crack over time and it's not a great indication of how solid they are (as most in UK arent mesh or fibre reinforced).

Yeh I did use primer, maybe I didn't use enough or the wrong type? It was the stuff that came with the uf heating.

I have tapped on it and I don't think it's loose.

One thing that could have had an effect the main central heating pipes run under this floor so that could have dried the floor out too quick. I did wet the floor before pouring the 2nd layer as well just to try and help with it potentially drying out too quick.

I did notice a bit of cracking on the first layer as well but it wasn't as bad.

MassiveJim · Monday at 11:24

SpeedFreak said:
you should have had it on a suitable backer board with taped joints and should have used a fibre re-enforced latex. Straight on ply is a no no. The tradies that said they never had an issue are cowboys and likely weren't called back to fix the problem because the householder went and found someone reputable second time around lol.

you win 1st prize for not reading my post properly.

ply was laid (with screws) directly to joists
6mm insulated backer board was laid (with screws only) directly to the ply.
Joints were taped.
backer board was primed
UF heating was laid/taped down etc.
screed was poured.
some repair work was carried out
screed was primed
another layer of screed was poured

now I have cracking.

MassiveJim · Monday at 11:26

200sols said:
Tradesmen are the worst bodgers out there though tbf

Use an S2 class adhesive when fixing the tiles.

will this stuff be any good ?

https://www.screwfix.com/p/mapei-wall-floor-tile-adhesive-grey-20kg/4367d#product_additional_details_container

All the others seemed to have a very quick curing time, since I am a tiling noob I chose this one to give myself more time to work with it.
It's not an issue to get something else though if its no good

MassiveJim · Monday at 12:27

SpeedFreak said:
sorry, missed the bit with backer board!

Comment on fibre re-enforced remains though.

I had seen fibre re-enforced mentioned in conversations during my research and it was pretty much summed up as, its not something we use in the UK ie not readily available.

That being said the plumber that fit our main bathroom used self levelling (a different brand) didn't use fibre and that didn't crack
His pour was thicker though, about 10mm one end of the bathroom and 18mm the other if memory serves, so I'm not sure if that effects things.
The only difference in our main bathroom was the backer board was either 10mmor 12mm insulated board but I wouldn't have thought that would effect anything as the cement layer is the same thickness it is only the insulation in the middle that is thicker.

MassiveJim · Monday at 15:37

SpellowHouse said:
I just go clean over the heating element with the tile adhesive. I am not even sure why you would want to use self-levelling, it's all very well, but a good tile adhesive has better properties, and you really shouldn't need to level a plywood floor. Just level the tiles!!

I debated doing it that way but I'm a tiling noob, I don't want to accidently damage the UF heating element so opted to make my life easier.

200sols said:
Not really. You really want the S2 for added flexibility. Most do seem to be a rapid set though. I've used a lot of this stuff but its a bit of a pig to work with.

Ultra Tile Fix ProFlex Rapid Set S2 Fibre Reinforced Flexible S2 Adhesive Grey 20kg

Ultra Tile Fix ProFlex Rapid Set S2 Fibre Reinforced Flexible S2 Adhesive Grey 20kg from Pro Tiler Tools. Free UK delivery on most orders over £250 net, order online today.

www.protilertools.co.uk

When you said cement boards I assumed you meant proper cement boards and not XPS boards. I assume you used washers?

no, didn't use washers.

I've ordered some more adhesive, amazon was cheapest.

MassiveJim · Monday at 15:44

200sols said:
OK. That's the mistake then, you have to use washers when screwing down xps boards.

do I need to rip it all up then or will it be ok using S2 adhesive ?