"Phil L" wrote

There's a sketch here to show how it should be:

http://tinypic.com/view.php?pic=2ztccns&s=5

click on the pic for a better view.



The sandy stuff is sand blinding, this is put underneath the membranbe so
that it doesn't puncture during the concrete laying.

If this patch is an addition to the floor, IE laid long after the main
floor slab and not part of it, then it will need to be dug out and
replaced, so that you can insert a suitable membrane below it.

It's possible that water is getting underneath the door frame, have you
checked the sealant underneath the patio door?


--
Phil

Thanks for taking to time to read and respond.

Yes, as the patio door was not an original feature, the strip above the
inner blocks was added with the patio door.

I haven't excavated serious amount of this floor strip out yet because
insurance company is involved and maybe I can get them to do it.
From the little I can see though, some of the dpm is damaged where it wraps
over the top edge of the inner block and damp is concentrated in that area
..
So the only accessible bit of dpm at this point is the top broken edge
emerging from between the floor slab and the inner block. My question is:
how do I attach dpm to this top edge to lay over the inner block?

Also there is sand above the dpm rather than below it from what I can see.

Hope all this makes more sense.

Phil