Lifting karndean questions about sub floor

My husband is now saying that he thinks it's the original screed (cement and sand per our basic survey) and that my brother put a self levelling compound down to level up the floor, after filling the pipe repair and new rad pipe channels with concrete.
Also, as advised by the fitter, we removed the black (marley? / thermoplastic) tiles and adhesive under it before the SLC was put down.

The house was built in 1973 so now worried that this might have been the only damp proofing, or if there is any under the concrete, that it has failed. Is that likely or possible? Is there a way of finding this out (I don't have plans and can't track down the builders) other than someone drilling down and from what I understand potentially puncturing a DPM if there is one?

And if there is no trace of primer (as cream/beige surface under tile - presumably SLC? - looks painted, and on back of the latex (dark grey) firmly attached to it with the strong adhesive) - nothing red, green or black), does that mean the first lot of SLC has failed, or could it have reacted with the fitter's SLC? I remember him saying something about always putting his own SLC down as he wouldn't trust a builders, but no moisture testing was done that I know of.....

Whatever has caused this, what should we do to prevent further problems when we re-do the floor.
Do we get it grinded back to the screed and then put a liquid epoxy DPM down ? If so is 1 coat enough?
I don't understand the difference between primer and DPM. If primer had been used between SLCs would we have had no issues?
And is the likely cause any clearer from all of this?! If not, what can we do to be sure as can't afford to do this a 3rd time!

A flooring company (per my description) suggested that the base was very dry and sucked the moisture out of the SLC hence the bit of pitting as well as the cracks? Or that the top SLC was simply too strong for the sub base?
There seems to be a myriad of possible causes and I am very wary of the same thing happening again and worried that there isn't a consensus.

Your views and professional knowledge and experience would be much appreciated....

 

And could it be that the leak that was repaired wasn't dried out for long enough before the SLC was put down?

 

That dpm looks like Laybond rapid dpm which is the wrong type for that age sub floor.

what should happen.

Grind sub floor clean
If floor is smooth then a coat of ardex DPM1c if not do a coat of ardex NA screed

then prime ardex P4 then Ardex NA Screed on top

 

Thanks for the reply but confused astas photo isn't mine! So not sure if your reply relates to my post?
Would latex on top of a different SLC cause a reaction if no primer used?
And could removal of Marley tiles ( as advised to do by fitter) cause the failure of the first lot of SLC? Or would 2 layers of presumably different SLCs always come apart in high traffic area with central heating pipes under it?

Thanks

 

Rip up start again unfortunately. I do have a lovely neo grinder to remove your problem latex

 

What Karndean is it..?

I seem to have a fair few dozen assorted discontinued boxes form over the past couple of decades... If I have one, I can sell and courier. Though it almost certainly wouldn't batch match - plus 13 years can change the shade...