Correct preparation for self levelling compound?

Hi. I was going to put laminate over the existing (awful) tiles in our soon to be utility room. However, there is a toilet in the room and closer inspection shows that the previous owners have already put ceramic tiles over the original vinyl floor tiles, this is evident from the way that the toilet base, waste pipe and skirtings are embedded in the tile layer. I'm changing the toilet so I concluded there was no easy option, the ceramic tiles have to come up. I've now lifted the ceramic, adhesive and vinyl tile, just concrete with some thin patches of vinyl adhesive left.

I am aware that laminate is not usually the best option for a utility/wc but we already have the laminate, we did the entire ground floor with it apart from this one room. It's easy enough to change if it turns out there is a problem.

I've never used self levelling compound before. The room is only 4sqm (2m x 2m).

That's the background, now the questions I hope someone can help with;
1. The house is 30 years old and has a DPC. Do I need a membrane of some sort on the concrete or between levelling compound layer and underlay/underlay and laminate?
2. Is a primer needed before applying the self leveller?
3. How 'good' (level) does the surface have to be before applying the self leveller? Is it ok as long as all peaks and troughs are covered or is there a more scientific consideration (e.g. minimum depth). The default variance will be around 3mm if I don't spend a couple of days working on it.
4. Do I really need to level the floor? It's sound, just has a 1 - 2mm variance due to patches of old vinyl adhesive. I'm now wondering if I could just use 5mm underlay boards and forget the screed?

Every job I do in this house seems to take twice as long as it should because I'm trying to right wrongs done by the previous owners - who bought the house brand new!

Thanks in advance.

BTW, I have now read mattsupra's excellent sticky posts on the subject. I'd still feel more confident with some advice for my specific situation though...

It would be nice to neutralise the residue adhesive, primer and screed would be ideal. Sometimes a clicking noise appears as the adhesive releases on the underlay when you walk on it.

Thanks for the suggestion. I'm afraid I'm going for the easiest short term option and will redo later if necessary. The adhesive residue is no longer tacky, just leaves a 1 - 2mm variation across the entire floor. I'm gone for Aquastop 5mm underlay.
Cheers

Rob3D said:

Thanks for the suggestion. I'm afraid I'm going for the easiest short term option and will redo later if necessary. The adhesive residue is no longer tacky, just leaves a 1 - 2mm variation across the entire floor. I'm gone for Aquastop 5mm underlay.
Cheers

Click to expand...

sounds like you should be ok and good to go