I have fitted insulation sheets on top of flex adhesive, but the result is not good as the sheets are not level. I have slightly raised sections and parts that slope slightly. I started off with SLC, but made the mix too thick meaning it didn't flow properly and refused to level as it set in 15mins. I sanded the SLC and decided I could get the insulation level on the adhesive bed. Wish I could start over, but have spent £400 on materials. Wish I had called in a professional. Can I use SLC on top of the insulation using a better mix followed by adhesive, or can I get the tiles level on an adhesive mix?

it depends on how far out the sheets have been set mate.

if your talking a few mm then you could sort it out with adhesive bed.

you could also fill in patches prior to tiling over the sheets.

welcome to the forum mate, register and you will have better access to the forums and you can browse through various sections of the forum.

You'll be banging your head on the ceiling if you carry on adding layers! Joking aside, yes you can SLC over the insulation boards but there is quite a knack to getting it flat and level, get a pro with experience to do this part for you, it shouldn't cost you much in labour and will at least give you a fighting chance of getting a nice flat tiled floor.

Thanks for the replies. Height is indeed a problem as there is a low beam in the kitchen. I have a straight metal edge that I am using together with a spirit level and have marked out where the raised sections and troughs are. If I use normal setting tile adhesive instead of the rapid set that I used beneath the insulation, would I be left with enough time to adjust adhesive as I lay? Is this a good approach. If not, I will get a professional to add a layer of SLC as advised before continuing. Thanks.

If you do self level over existing I tend to prime it.

hi there,get a pro in to level it,yes you will have to buy some more slc and pay a days wages but it will be sorted

Welcome to the forum. as whitebeam said you need to prime the first layer allowing it to bond correctly!