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I've taken tiles up in a ground floor bathroom. The floor is concrete (same as the rest of the house), with what looks like bitumen dpc. There seems to be a patch that seems damp and the concrete thin/sandy? I was going to use self leveller before putting down lino (so that the floors feel a bit warmer under foot)! What is the best approach to fix / sort this before moving ahead? The pictures hopefully show the issue.

Hi lydialala,
In view of the age of your house it may be that there was no integral DPM but bitumen adhesive/paint with a layer of asbestos based tiles formed the DPM. Suggest you remove all loose material, paint a couple of layers of bituminous paint over the whole floor, then apply a layer of self levelling compound. It’s probably best to remove the loo pan until there is a new surface.
Regards S

Thank you for replying, much appreciated. Having looked at it closer I think the waste from the shower goes across there. That's the only place for it to head outside (I believe it's going under the toilet waste, so I think the reason for the difference in the floor is that they've dug down to put that in, and not put any dpc back on top when they backfilled and covered it.

Hi lydialala,
Thanks for the update_
It’s worth cleaning out the hole and see if you can find any trace of a DPM.
Regards S