TheScullster wrote:
Hi all - bit long this one sorry (no piccys available)

I have a damp problem which appears to be coming from the strip of
floor just inside my patio doors.
Originally this damp was believed to be due to a leaking pipe, so a
channel to the room side of this strip has been excavated to show the
pipes.
To clarify - considering the view from the inside out there is:

Floor slab
Channel in floor with pipes in right on edge of slab
Edge of floor dpm
Inner leaf of block work with concrete capping to level with existing
floor Inside face of patio door


I think I understand.

The damp proof membrane for the original main slab ties into the wall
dpc at top of main slab level.

yes.

This means that any dpc/membrane below the strip of floor immediately
inside the patio door (above the inner block leaf) can only have a
membrane below the level of the wall dpc alongside it. I should

I can't make head nor tail of any of this.


point out that this patio door is not an original feature of the
property and is effectively a window extended to ground level IYSWIM,
although a patio door has been there for 20 years or so.

So I guess the questions are to do with the way this area should be
made up. If this door was installed from scratch, the brickwork would
be cut down below the window but what then?

1. Is the exposed cavity filled with anything down to foundation
level (concrete)?

It can be but usually isn't, the cavity is normally filled with 50mm
polystyrene up to about 50mm below the floor surface, then faced up with
mortar / concrete

2. How is the dpm for the room slab connected to dpc under this
strip of added "floor"?

What do you mean, 'added floor'?

3. Should the floor strip be just concrete, cast over dpc?

I assumed the floor slab was poured in one?

4. How is the concrete strip supported over the cavity, if the
cavity isn't filled?

See above.

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.


Having poked about a bit, the damp appears to be coming from the area
outside the main floor dpm, under this strip of floor.
Under the concrete strip there seems to be loose sandy stuff. I am
looking at a small area alongside the pipe channel about 600 (2')
long. Although there is some dpm under the strip it is clearly
damaged in parts. The insurance company put some driers in over the past
fortnight, but
within an hour or two of them being turned off, damp came back to the
sandy area beneath the floor strip.
If there is no "active" water source (i e. if it were down to ground
water only) would damp reappear that quickly?

Anyone who's read this far deserves a medal - any help or advice
appreciated.

TIA

Phil

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 L
RSRL Tipster Of The Year 2008