Hi. I have recently (one week ago) poured self levelling compound onto a kitchen concrete floor to correct a slope of about 40mm at it's lowest. I have used a compound which states min thickness 3mm, max thickness 80mm. Unfortunately hairline cracks showed up around the edges of the leveled area, like 200mm off the walls.
Here is what I did:
Cleaned thoroughly existing concrete
Primed 3:1 SBR with water onto floor. Allowed 24h to dry.
Applied 2nd coat SBR 1:1 with water. Allowed 24h to dry
Applied 3rd coat SBR neat. Allowed 48h to dry
Applied a couple of lines of expanding foam around the edges to allow for floor expansion.
Mixed compound according to manufacturer's instructions. I did noticed though the guy who helped me with mixing run the water hose once around the bucket walls to clean a bit the mix going up during mixing. This extra water went into that mix. Told him not to do that as it adds excess water to the mix.
Poured mix on floor, troweled around to bond the mixes as poured. Could not spike-rolle as the compound was too deep for the spikes.
So now the compound is rocksolid in the middle of the floor but hairline cracked around the edges. Did a sound test with hammer and it only sounds hollow-ish in the corners where cracks are more abundant.
I spoke to tech support at compound manufacturer showed pictures and they said, not sure but it might have been too much water in the mixes. (Hose in bucket came to mind).
I am not sure what to do now. Do I have to lift and redo the cracked compound? If yes, all around where it cracked or just where it sounds hollow-ish?
Someone suggested because I will have kitchen units around the walls on top of the cracked areas, just put Ditra Heat mesh on top of the compound everywhere and tile on top of Ditra and I will never have the cracks bother me. Is this safe or it will bite my bum later on?
What is your advice, what would you do at this stage? And why do you think the cracks happened?
Many thanks for any replies!
Are you a tradesperson and able to answer this question?
Hi There
The Ditra mate is best idea to do. I think there was too much of SBR on the concrete surface under and the selfleveling didn't bond properly with the subfloor.
hi there!...from my experience if u gonna use ditra matt before tiling wouldn.t be any issues in the future...i have used ditra matt on the new screed which are making cracks like yours and not any issues from 10 years ago untill now...what i see there is not the self levelling problem...if underneath was screed the self levelling alone couldn.t avoid the screed cracks from expanding and contracting and that.s a reason why the cracks appear...when i have this cases i do ditra matt first and then self levelling after which will keep it without cracks...but what i suggest you to to is to use ditra matt before tiling and i can warranty there wouldn.t be any cracks in the future if the ditra is done in a good standard...hoppefully i could help you with my advice
Hi, firstly, if you use any matting (no need to use ditra as there are cheaper versions but it is good) then don't worry about these cracks at all.
If not using the matting, I still wouldn't worry if they're just hairline. In my experience, some brands (like the ultra from topps tiles) always does this. Just seems to be how some of them dry so I've stopped using Ultra for that reason. It was installed correctly so the fault is with the leveller. It'll be fine.
Interesting one this, but adding additional water to the mix won't be an issue. I was trained to add around a litre of extra water per 25kg bag to make the mix run smoother, sometimes the mix is too stiff using the guideline values and doesn't level correctly due to this.
If you hare putting underfloor heating in using a wire I would not be putting the wire under the units!! All wires I have used state there should be a 50mm or so void between the wire and any objects on top of it, cupboard, toilets, vanity units etc...
If the cracks are going to be under the units then I would not bother about the cracks. I am assuming these are only hairline cracks and therefore not going to cause any bother. Once the available floor space has the heating matt and tiles down then everything should be perfecto.
One possible cause for the cracking could be a bag being either out of date or there has been air getting into it. I have had that before when the bag has "gone off". That is a pain in the backside.
I've never put a ring of foam around the edges for expansion - does it tell you to do this? Could there be potential problem that the foam hasn't fully expanded by time you have put the levelling screed down? Therefore creating additional stress near the edges?
