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

The damp proof membrane for the original main slab ties into the wall dpc at
top of main slab level.
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 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)?
2. How is the dpm for the room slab connected to dpc under this strip of
added "floor"?
3. Should the floor strip be just concrete, cast over dpc?
4. How is the concrete strip supported over the cavity, if the cavity isn't
filled?

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

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

"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

thescullster wrote:
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 .

The inner block should come up to floor level - if someone in the past has
broken the top edge of this block off for some reason, it's almost certainly
rising damp coming up from below ground via the blocks and a DPM isn't going
to seal properly on a broken block.


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

underfloor DPM is normally overlapped by 500mm to keep damp out of the
concrete.
It seems like someone has taken up a strip of concrete where the floor meets
the wall, possibly to make a channel for the pipes, and because the inner
block is easier to remove than concrete, they've taken this out and then not
joined the DPM properly to the existing underfloor DPM.

To do it properly, they obviously wouldn't take up 500mm of concrete in
order to get the required overlap, so it should have been overlapped as much
as possible, say about 100 - 150mm and glued, either with silicone or some
other waterproof sealant.

this is what will need to be done now if it's ever to be dry again.

And if the pipes are copper, they will need to be wrapped in PVC tape prior
to concreting.

--
Phil L
RSRL Tipster Of The Year 2008

"Phil L" wrote

underfloor DPM is normally overlapped by 500mm to keep damp out of the
concrete.
It seems like someone has taken up a strip of concrete where the floor
meets the wall, possibly to make a channel for the pipes, and because the
inner block is easier to remove than concrete, they've taken this out and
then not joined the DPM properly to the existing underfloor DPM.

To do it properly, they obviously wouldn't take up 500mm of concrete in
order to get the required overlap, so it should have been overlapped as
much as possible, say about 100 - 150mm and glued, either with silicone or
some other waterproof sealant.

this is what will need to be done now if it's ever to be dry again.

And if the pipes are copper, they will need to be wrapped in PVC tape
prior to concreting.

Phil

Thanks for all your help with this.
Knowing how things should be will help when the insurance contractor comes
back - particularly if he starts spinning yarns/spouting the BS.

Phil

On 23 Feb, 08:29, "TheScullster" wrote:
"Phil L" wrote



underfloor DPM is normally overlapped by 500mm to keep damp out of the
concrete.
It seems like someone has taken up a strip of concrete where the floor
meets the wall, possibly to make a channel for the pipes, and because the
inner block is easier to remove than concrete, they've taken this out and
then not joined the DPM properly to the existing underfloor DPM.

To do it properly, they obviously wouldn't take up 500mm of concrete in
order to get the required overlap, so it should have been overlapped as
much as possible, say about 100 - 150mm and glued, either with silicone or
some other waterproof sealant.

this is what will need to be done now if it's ever to be dry again.

And if the pipes are copper, they will need to be wrapped in PVC tape
prior to concreting.

Phil

Thanks for all your help with this.
Knowing how things should be will help when the insurance contractor comes
back - particularly if he starts spinning yarns/spouting the BS.

Phil

I think this could be summed up as "bridging the cavity at a doorway".
On my build, there will be 65mm screed on top of the concrete slab,
and this needs to pass over the cavity to form a continuous floor
across to the door which is fitted in the outer leaf.
The inner blocks come up to the top of the slab, but not to top of
final floor level. The DPC from the walls is cut off at the door
opening. The DPM from the slab is actually long enough to cross the
cavity. But I was recommended to bridge the cavity with slate, then
screed on top of this across the cavity. The cavity closer will be
fitted before the screed and slate, and act as a sideways damp course
between the side of the brick opening and the screed.
I can see there are a few "corners" where damp could leak. I may paint
the area with liquid rubber just to be sure.
The earlier advice to have the inner leaf up to the floor level would
not work, since there would be no room for any screed on top, and any
self-levelling compound over screed and onto bricks / blocks would
forever cause problems. Basically, the screed must be seemless across
the cavity to the actual door frame / threshold.
Simon.

wrote

I think this could be summed up as "bridging the cavity at a doorway".
On my build, there will be 65mm screed on top of the concrete slab,
and this needs to pass over the cavity to form a continuous floor
across to the door which is fitted in the outer leaf.
The inner blocks come up to the top of the slab, but not to top of
final floor level. The DPC from the walls is cut off at the door
opening. The DPM from the slab is actually long enough to cross the
cavity. But I was recommended to bridge the cavity with slate, then
screed on top of this across the cavity. The cavity closer will be
fitted before the screed and slate, and act as a sideways damp course
between the side of the brick opening and the screed.
I can see there are a few "corners" where damp could leak. I may paint
the area with liquid rubber just to be sure.
The earlier advice to have the inner leaf up to the floor level would
not work, since there would be no room for any screed on top, and any
self-levelling compound over screed and onto bricks / blocks would
forever cause problems. Basically, the screed must be seemless across
the cavity to the actual door frame / threshold.
Simon.

Thanks Simon
I think you have managed to clarify the situation somewhat here.
Can you explain what this cavity closer business is about please?
Is it the polystyrene cavity fill that Phil mentioned and showed in his
picture?
Can I do all this without removing the patio door? The above-slab screed
appears to go up to the face of the door sill rather than under it IYSWIM.
Also the patio door has a clearly visible black dpc under the sill.
Presumably the slate that you mentioned sits on top of the inner block and
across the cavity. In my case this would have to perch on the edge of the
outer block (assuming there is room left before the patio door frame).
Are you abandoning the dpm over the cavity completely - if not, where is it
going?
Are you talking about painting the slate and brick with rubber, or is this
over the top of the screed as a final sealer?

TIA

Phil

On 23 Feb, 11:57, "TheScullster" wrote:
wrote



I think this could be summed up as "bridging the cavity at a doorway".
On my build, there will be 65mm screed on top of the concrete slab,
and this needs to pass over the cavity to form a continuous floor
across to the door which is fitted in the outer leaf.
The inner blocks come up to the top of the slab, but not to top of
final floor level. The DPC from the walls is cut off at the door
opening. The DPM from the slab is actually long enough to cross the
cavity. But I was recommended to bridge the cavity with slate, then
screed on top of this across the cavity. The cavity closer will be
fitted before the screed and slate, and act as a sideways damp course
between the side of the brick opening and the screed.
I can see there are a few "corners" where damp could leak. I may paint
the area with liquid rubber just to be sure.
The earlier advice to have the inner leaf up to the floor level would
not work, since there would be no room for any screed on top, and any
self-levelling compound over screed and onto bricks / blocks would
forever cause problems. Basically, the screed must be seemless across
the cavity to the actual door frame / threshold.
Simon.

Thanks Simon
I think you have managed to clarify the situation somewhat here.
Can you explain what this cavity closer business is about please?
Is it the polystyrene cavity fill that Phil mentioned and showed in his
picture?

At the edge of an opening, the cavity must be closed somehow. Old
method was the inner leaf turned 90 degrees and met the outer,
vertical DPC put in where they meet. New method, a top hat shaped
insulated strip is pushed into the cavity and the two flaps are used
to fix it to the blocks/bricks either side. This is kind of similar to
the polystyrene cavity fill, and will block the path of damp.

Can I do all this without removing the patio door? *The above-slab screed
appears to go up to the face of the door sill rather than under it IYSWIM..

Depends. If the door is only fixed to the outer leaf, you should be
able to remove the infill right up to the door. If the door/sill
overlaps an infilled cavity, it might be trickier.
The screed will go up to the door sill, since the sill/door is
commonly set lower down in the outer leaf, so there is less height to
step over to get out ! Also, screed going under and exposed to the
outside would not be good idea !

Also the patio door has a clearly visible black dpc under the sill.
Presumably the slate that you mentioned sits on top of the inner block and
across the cavity. *In my case this would have to perch on the edge of the
outer block (assuming there is room left before the patio door frame).

Yep, there should be a small bit of outer leaf remaining to sit the
slate on (assuming standard PVCu profiles). Else, the infill material
in the cavity would support it. If DPC under the (plastic ?) door, the
slate would sit on top of this. But can't see the point in a DPC under
a plastic door really.

Are you abandoning the dpm over the cavity completely - if not, where is it
going?

Well, slate would act as a DPM under the cavity by itself, but note
that the DPM from under the slab should tie into the wall DPC. In this
case I would lap a length of DPM across the cavity and under the
slate. This maintains the waterproof barrier

Are you talking about painting the slate and brick with rubber, or is this
over the top of the screed as a final sealer?

I meant since the DPC / DPM detailing is a bit fiddly around the
doorway, with various corners etc, I would paint the sides of the
inner leaf a little way up, and the inner leaf bottom edge before
lapping the DPM onto it, just as a precaution. But I bet no builder
would be so fussy !

Hope that helps,
Simon.

wrote

snip...................
I meant since the DPC / DPM detailing is a bit fiddly around the
doorway, with various corners etc, I would paint the sides of the
inner leaf a little way up, and the inner leaf bottom edge before
lapping the DPM onto it, just as a precaution. But I bet no builder
would be so fussy !

Hope that helps,
Simon.

Brilliant - thanks for the detail Simon!
Don't care how fussy I need to be, as long as the problem is fixed in one
hit.

Phil