Hi all

Tricky one this.
Four years ago I bought a 1970s dump and discovered that a damp patch
(believed to be a leaking patio door) was actually a fractured water pipe.
A copper 15mm elbow had split on its internal "corner?" on a buried hot
water feed to a sink and was showing as a damp-to-wet area of floor.
On further investigation, water had obviously saturated the sub-base and
travelled along all heating channels rising in places to rot skirtings etc.
I lifted all the plastic? tiles that had been bitumened over the ground
floor and a film of water was found under most of them.
As I say, that was four years ago and since then, all the upper surface of
the ground floor slab appears to have dried out (sorry, forgot, solid
concrete ground floor).

But, even now, I have discovered that if something impermiable is placed
over the limit edge of the floor dpm where it rises to floor level (eg at
all internal and external door thresholds), a damp film forms on its
underside. This is true of a rubber backed doormat at the front door and a
length of skirting which was being stored close to the rear patio door.

So the question is - how long should it take for the entire sub base to dry?
Is it likely that this damp is coming from "outside" rather than "inside"
the dpm IYSWIM? (ie it is general ground water rather than a leak)

This is causing concern for two reasons:

1. I am considering converting heating system to sealed and am concerned
about possible leaks.
2. SWMBO was after wood floor in the dining room (with patio door) and I'm
not sure whether I should consider this if there is a source of damp
(however minor) beneath it.

Is it possible to locate minor leaks without actually digging up all the
floor channels?

Thanks to anyone who's got this far.

Phil

TheScullster wrote:
Hi all

Tricky one this.
Four years ago I bought a 1970s dump and discovered that a damp patch
(believed to be a leaking patio door) was actually a fractured water pipe.
A copper 15mm elbow had split on its internal "corner?" on a buried hot
water feed to a sink and was showing as a damp-to-wet area of floor.
On further investigation, water had obviously saturated the sub-base and
travelled along all heating channels rising in places to rot skirtings etc.
I lifted all the plastic? tiles that had been bitumened over the ground
floor and a film of water was found under most of them.
As I say, that was four years ago and since then, all the upper surface of
the ground floor slab appears to have dried out (sorry, forgot, solid
concrete ground floor).

But, even now, I have discovered that if something impermiable is placed
over the limit edge of the floor dpm where it rises to floor level (eg at
all internal and external door thresholds), a damp film forms on its
underside. This is true of a rubber backed doormat at the front door and a
length of skirting which was being stored close to the rear patio door.

So the question is - how long should it take for the entire sub base to dry?
Is it likely that this damp is coming from "outside" rather than "inside"
the dpm IYSWIM? (ie it is general ground water rather than a leak)

This is causing concern for two reasons:

1. I am considering converting heating system to sealed and am concerned
about possible leaks.
2. SWMBO was after wood floor in the dining room (with patio door) and I'm
not sure whether I should consider this if there is a source of damp
(however minor) beneath it.

Is it possible to locate minor leaks without actually digging up all the
floor channels?

Thanks to anyone who's got this far.

Phil

I started a job a few weeks ago in a living room ext to take up the
screed with the intention of putting battens and a t&g floor down but
soon realised that all was not as it should be.
The cowboy who built the extention was to tight to put a dpc in so are
you sure that you don't have the same problem.
The thing I find odd though though is whilst the builder was to tight
to by a membrane he through enough bricks to build a wall into the
concrete base and then went out and bought thermalite blocks.
I say concrete base but used the term concrete lightly.

Kevin

"Kev" wrote

snip...........
The cowboy who built the extention was to tight to put a dpc in so are
you sure that you don't have the same problem.

Thanks Kev

No the top edge of the dpc is visible and the damp is in the original house
rather than an extension.
Could the damp be coming from below the dpc and up the "outside" of it?
I know the floor dpc should lapped into the wall dpc to prevent this, but I
suspect it is damaged in parts.

Phil

TheScullster wrote:
"Kev" wrote

snip...........
The cowboy who built the extention was to tight to put a dpc in so are
you sure that you don't have the same problem.

Thanks Kev

No the top edge of the dpc is visible and the damp is in the original house
rather than an extension.
Could the damp be coming from below the dpc and up the "outside" of it?
I know the floor dpc should lapped into the wall dpc to prevent this, but I
suspect it is damaged in parts.

Phil

I'm not too clear on the details of what youre describing but below the
dpc will always be damp. If youre getting damp up at floor level from
below dpc, your dpc is not sealing somewhere. You can use a liquid
sealant on a concretef loor slab to remedy this.


NT

"TheScullster" wrote in message
...
Hi all

Tricky one this.
Four years ago I bought a 1970s dump and discovered that a damp patch
(believed to be a leaking patio door) was actually a fractured water pipe.
A copper 15mm elbow had split on its internal "corner?" on a buried hot
water feed to a sink and was showing as a damp-to-wet area of floor.
On further investigation, water had obviously saturated the sub-base and
travelled along all heating channels rising in places to rot skirtings
etc.
I lifted all the plastic? tiles that had been bitumened over the ground
floor and a film of water was found under most of them.
As I say, that was four years ago and since then, all the upper surface of
the ground floor slab appears to have dried out (sorry, forgot, solid
concrete ground floor).

snip

If I recall correctly there is a problem with deterioration of copper pipes
buried in concrete (Isn't this why copper gas pipes are clad in plastic?) If
that is the case do you have any more buried water pipes that may be
leaking?

Tony

TMC wrote:
"TheScullster" wrote in message
...
Hi all

Tricky one this.
Four years ago I bought a 1970s dump and discovered that a damp patch
(believed to be a leaking patio door) was actually a fractured water pipe.
A copper 15mm elbow had split on its internal "corner?" on a buried hot
water feed to a sink and was showing as a damp-to-wet area of floor.
On further investigation, water had obviously saturated the sub-base and
travelled along all heating channels rising in places to rot skirtings
etc.
I lifted all the plastic? tiles that had been bitumened over the ground
floor and a film of water was found under most of them.
As I say, that was four years ago and since then, all the upper surface of
the ground floor slab appears to have dried out (sorry, forgot, solid
concrete ground floor).

snip

If I recall correctly there is a problem with deterioration of copper pipes
buried in concrete (Isn't this why copper gas pipes are clad in plastic?) If
that is the case do you have any more buried water pipes that may be
leaking?

Tony

IUC the risk of corrosion is higher, but still very low. Lots of gas
pipes are buried in crete up and down the country, and resulting leaks
are not a significant prolbem.

NT

"TMC" wrote

If I recall correctly there is a problem with deterioration of copper
pipes buried in concrete (Isn't this why copper gas pipes are clad in
plastic?) If that is the case do you have any more buried water pipes that
may be leaking?

Tony

Thanks Tony

Yes, all the ground floor piping is buried copper. I was hoping someone
might have a clever method to locate leaks and confirm if there are any.
All I can think of is to tie up the ball valve in the heating header tank
for a short while and monitor the water level closely. Not sure that this
will highlight leaks which are just big enough to cause pressure loss in
heating system though.
As noted in the original post, when I took over the place, the floor and
sub-base must have been sodden.

In my last place, built in 1988, all buried copper pipes were plastic
coated.
In the present earlier build property, they seem to have been clad in some
hession sort of stuff and laid in sand filled channels before concreting
over (both gas and water).

Phil

wrote

I'm not too clear on the details of what youre describing but below the
dpc will always be damp. If youre getting damp up at floor level from
below dpc, your dpc is not sealing somewhere. You can use a liquid
sealant on a concretef loor slab to remedy this.

Thanks NT

The damp is not appearing as visible in the surface of the floor slab at
all.
It is presumably evaporating or tracking up from below (not sure which side
of the dpm) and arriving on the underside of objects placed over cracks in
the floor where the edge of the floor membrane stops.

Maybe I just need to fill the cracks with water-proof sealant?

Phil

TheScullster wrote:
The damp is not appearing as visible in the surface of the floor slab at
all.
It is presumably evaporating or tracking up from below (not sure which side
of the dpm) and arriving on the underside of objects placed over cracks in
the floor where the edge of the floor membrane stops.

Maybe I just need to fill the cracks with water-proof sealant?

Thre may be a bit of a draught bringing in damp air. I'd be inclined to
cap odd the void with some sort of mastic, rather than filling it up.

On Fri, 23 Jun 2006 13:44:33 +0100, "TheScullster" wrote:

All I can think of is to tie up the ball valve in the heating header tank
for a short while and monitor the water level closely. Not sure that this
will highlight leaks which are just big enough to cause pressure loss in
heating system though.

Could you substitute air for water, and do a drop test, or some such?

Thomas Prufer

on 23/06/2006, TheScullster supposed :
"TMC" wrote

If I recall correctly there is a problem with deterioration of copper pipes
buried in concrete (Isn't this why copper gas pipes are clad in plastic?)
If that is the case do you have any more buried water pipes that may be
leaking?

Tony

Thanks Tony

Yes, all the ground floor piping is buried copper. I was hoping someone
might have a clever method to locate leaks and confirm if there are any.

Connecting a high resistance meter to a suspect pipe, one probe to pipe
the other to a damp area might provide some usable clues - the lower
the resistance the nearer you might be to a possible leak. I would not
rely too heavily on the outcome, but along with other clues it might be
of use.

If it uses a header tank, could you perhaps shut the ball valve supply
off and see if the level in the tank drops?



--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk