Got an exterior wall that gets damp. Sometimes it's damp, sometimes not.
The dampness is always in the first 18" above the skirting board. The wall
does not have a cavity and it's always cold. I suspect the dampness in
condensation rather than rising/penetrating, especially as sometimes it is
enough to run down and sit in a pool on the top of the skirting. Am I
right?

John

The dampness is always in the first 18" above the skirting board. The
wall does not have a cavity and it's always cold. I suspect the dampness
in condensation rather than rising/penetrating,

Why do you think this?

It could very well be a failed/missing/bridged damp proof course. This is
easily remedied with a chemical injection. The expensive part is replacing
all the plaster.

If it really is condensation, this can be fixed by additional insulation and
ensuring adequete ventilation.

Christian.

Christian McArdle wrote:
The dampness is always in the first 18" above the skirting board.
The wall does not have a cavity and it's always cold. I suspect the
dampness in condensation rather than rising/penetrating,

Why do you think this?


It's the coldest surface in teh room, and I didn't think penetratin damp
would accumulate enough to run down and collect, whereas I know condensation
does that.

It could very well be a failed/missing/bridged damp proof course.

Indeed the concrete outside is at a slightly higher level than the floor
inside, however the damp inside does not seem to coincide with the damp
inside, ie it can be dry inside when rainy and wet inside when fine out.
Also the wall along which the damp is present is quite sheltered from the
rain, which doesn't collect.

This is easily remedied with a chemical injection. The expensive part
is replacing all the plaster.

Can the injection not be done from the outside?


If it really is condensation, this can be fixed by additional
insulation and ensuring adequete ventilation.

I just want to make sure I know where it comes from before I take measures.
Any tips?


Thanks

John

Can the injection not be done from the outside?

It is done from the outside. However, it requires the plaster inside to be
replaced, as it will be damaged and contaminated with salts or something.
Besides, it creates additional work for the damp proofing specialist.

OTOH, you seem to suggest the the inside floor is lower than the outside
ground. That would require tanking up to above the DPC layer, as there would
be no protection against rising and penetrating ground damp below the DPC
layer.

Of course, if it is condensation, rather than penetrating or rising damp,
none of this will help. However, the fact it is concentrated solely in the
very bottom of the wall might suggest a penetrating problem. However, I
suppose it could just be the proximity of the cold ground that causes a
condensation problem.

I assume you don't have/do anything silly, like unflued gas heating or
constantly drying clothes indoors?

Christian.

JK wrote:

Got an exterior wall that gets damp. Sometimes it's damp, sometimes not.
The dampness is always in the first 18" above the skirting board. The wall
does not have a cavity and it's always cold. I suspect the dampness in
condensation rather than rising/penetrating, especially as sometimes it is
enough to run down and sit in a pool on the top of the skirting. Am I
right?


Hard to tell. May be both. Its unusual for condensation to be at lower
levels only, but it can be if the wall is not getting heat there for
some reason. When I have had condensation it has formed over all the
outside wall, not just at the base. The only time I had that was in a
kitchen where it was both steamy,. and the wall base was covered by
units allowing no circulation.


I'd suspect a bridged damp course frankly, or none, giving classic
rising damp/penetration.

Check outside and see if the soil is above DPC level, and remove if it is.


Even if no DPC exists, you can vastly reduce penetration by digging a
trench round the affceted area and filling with shingle, provided it is
not in an area that is lower than local ground so it just forms a pond :-)



John

JK wrote:

Christian McArdle wrote:

The dampness is always in the first 18" above the skirting board.
The wall does not have a cavity and it's always cold. I suspect the
dampness in condensation rather than rising/penetrating,

Why do you think this?



It's the coldest surface in teh room, and I didn't think penetratin damp
would accumulate enough to run down and collect, whereas I know condensation
does that.



Yes, but it may be cold because its damp already



It could very well be a failed/missing/bridged damp proof course.


Indeed the concrete outside is at a slightly higher level than the floor
inside, however the damp inside does not seem to coincide with the damp
inside,


Run that past me again?

ie it can be dry inside when rainy and wet inside when fine out.
Also the wall along which the damp is present is quite sheltered from the
rain, which doesn't collect.



Mmm.



This is easily remedied with a chemical injection. The expensive part
is replacing all the plaster.


Can the injection not be done from the outside?



Yes, but the plaster is generally rotten and in need of redoing, also in
your case it probably needs to be done below soil level.




If it really is condensation, this can be fixed by additional
insulation and ensuring adequete ventilation.


I just want to make sure I know where it comes from before I take measures.
Any tips?



Its very hard to be sure. BUT you could try e.g. contact glung a load of
kitchen foil over teh wall. If it still gets sopping wet on teh inside
face, its at least partially condensation (which I suspect is some part
of the problem) but if that reduces the puddles, its likley to be coming
from behind the foil, and you may actually see the damp patch grow higer
as teh water sekks somewhere else to ooze out.

You may even have a leaking pipe nearby.



Thanks

John

Christian McArdle wrote:
Can the injection not be done from the outside?

It is done from the outside. However, it requires the plaster inside
to be replaced, as it will be damaged and contaminated with salts or
something. Besides, it creates additional work for the damp proofing
specialist.

OTOH, you seem to suggest the the inside floor is lower than the
outside ground. That would require tanking up to above the DPC layer,
as there would be no protection against rising and penetrating ground
damp below the DPC layer.


Indeed I'm coming to this conclusion. The back of the house has concrete
all round up to the walls so that tanking job would be a major hassle (ie
expense) as the concrete would have to broken first. Is it done with a
mastic, or something more solid?


Of course, if it is condensation, rather than penetrating or rising
damp, none of this will help. However, the fact it is concentrated
solely in the very bottom of the wall might suggest a penetrating
problem. However, I suppose it could just be the proximity of the
cold ground that causes a condensation problem.


No, I think you're right. The plaster shows years of tide marks so it does
look like it's coming from the ground.


I assume you don't have/do anything silly, like unflued gas heating or
constantly drying clothes indoors?


Nothing like that unfortunately.

Anyone know a reputable damp specialist in North London? Don't laugh.

J

The Natural Philosopher wrote:
JK wrote:



I'd suspect a bridged damp course frankly, or none, giving classic
rising damp/penetration.

None would be par for the course...must have been done on the cheap, it's an
addition built by the council in the 60's.



Check outside and see if the soil is above DPC level, and remove if
it is.


It is, but sadly any soil in the area is topped with a thick layer of
concrete right up to the edge of the house.




Even if no DPC exists, you can vastly reduce penetration by digging a
trench round the affceted area and filling with shingle, provided it
is
not in an area that is lower than local ground so it just forms a
pond :-)


I'm frightened that if I chisel away the concrete from around the wall I'll
destabilise the walls! The house is built on London clay so I have no idea
what the drainage would be like.

Would there be any mileage on stripping the plaster on the inside say up to
3' and painting something waterproof on the inside bricks then replastering?
Or would that just make the water com out higher up?

J

JK wrote:


Would there be any mileage on stripping the plaster on the inside say up to
3' and painting something waterproof on the inside bricks then replastering?
Or would that just make the water com out higher up?


Yes and no. Sort of.

IF you RENDER the inside with water resistant mortar, of course it will
come out higher, the trick is to make it come out on the OUTSIDE of the
house...I did this on one house and it definitely helped a bit, but it
wasn't a total solution.

I'd say injection is the way to go frankly. My previous house was rotten
with damp, some of which was rising. Where it had been injected it did
actually solbve th eproblem (suffolk clay)...sadly hu=ge areas on
internal walls and in partucular the fireplace couldn't be injected, and
that was where the rot was the worst, and the effloresence..



J

On Tue, 2 Dec 2003 17:17:38 -0000, "Christian McArdle"
wrote:

Can the injection not be done from the outside?

It is done from the outside. However, it requires the plaster inside to be
replaced, as it will be damaged and contaminated with salts or something.
Besides, it creates additional work for the damp proofing specialist.

Damp proofing what? These are the companies you need to supply
bales of hay to so they can feed their horses aren't they?
--
cheers,

witchy/binarydinosaurs

The Natural Philosopher wrote:
JK wrote:


I'd say injection is the way to go frankly. My previous house was
rotten
with damp, some of which was rising. Where it had been injected it did
actually solbve th eproblem (suffolk clay)...sadly hu=ge areas on
internal walls and in partucular the fireplace couldn't be injected,
and
that was where the rot was the worst, and the effloresence..

Well I guess I could try injection first. Tell me, is it possible to inject
on the inside? The lowest point on the outside would be around the top of
the skirting board on the inside, so I'm guessing I'd still have a proble.
Of course that problem would perhaps be behind the skirting so out of
sight...

The lowest point on the outside would be around the top of the
skirting board on the inside, so I'm guessing I'd still have a
proble.

The whole point is that the injection is done above the outside ground
level. Otherwise, you are swapping no DPC for a bridged one, which may be
better, but possibly not by much. The problem is that your floor level is
low, making it partly cellar.

Christian.

"JK" wrote in message ...

Indeed the concrete outside is at a slightly higher level than the
floor
inside,

problem located. The solution to the problem is to solve the problem.
Ie lower the concrete level outside. Since that will give you a lower
water collecting area you will also need to add a drain to prevent
water collection.



Check outside and see if the soil is above DPC level, and remove if
it is.

It is, but sadly any soil in the area is topped with a thick layer of
concrete right up to the edge of the house.


Would there be any mileage on stripping the plaster on the inside say up to
3' and painting something waterproof on the inside bricks then replastering?
Or would that just make the water com out higher up?

The solution to the problem is to solve the problem, not to do things
that dont solve the problem.


Regards, NT

It is, but sadly any soil in the area is topped with a thick layer of
concrete right up to the edge of the house.

Cut back concrete along the wall, dig trench, fill to brim with coarse
gravel.

--
Toby.

'One day son, all this will be finished'

Christian McArdle wrote:

The lowest point on the outside would be around the top of the
skirting board on the inside, so I'm guessing I'd still have a
proble.


The whole point is that the injection is done above the outside ground
level. Otherwise, you are swapping no DPC for a bridged one, which may be
better, but possibly not by much. The problem is that your floor level is
low, making it partly cellar.



Yes, but, injection DPC injects a whole area of brick anyway.

What they would probably do in a case like this is start holes above
gorund and agnle down from ourside, inject and hen you need to tank up
inside to the level of the injectors or a bit above. May have a problem
if water gets into the floor tho. Best solution would be something likke
a full DPM over the floor carried up the walls to above injection level,
screed and plaster afterwards



Christian.

"Toby" wrote in message
...
It is, but sadly any soil in the area is topped with a thick layer of
concrete right up to the edge of the house.

Cut back concrete along the wall, dig trench, fill to brim with coarse
gravel.

--
Toby.



A colonial drain.

Toby wrote:
It is, but sadly any soil in the area is topped with a thick layer
of concrete right up to the edge of the house.

Cut back concrete along the wall, dig trench, fill to brim with coarse
gravel.

This doesn't sound like a diy job. Not if you mean the application of one
of those terrifying massive grinders that pavement operatives use in busy
shopping centres to cut curbstones! How wide does such a trench need to be
anyway?

N. Thornton wrote:
"JK" wrote in message
...

Indeed the concrete outside is at a slightly higher level than the
floor
inside,

problem located. The solution to the problem is to solve the problem.
Ie lower the concrete level outside. Since that will give you a lower
water collecting area you will also need to add a drain to prevent
water collection.


You're right, but it's not an option. I need some kind of remedial
treatment for a problem created by bad design. Breaking up 10 sq metres of
concrete, digging out, installing drains is just too much, partly from a
cost point of view and partly because any mess has to be carted through the
flat to get it away.

JK wrote:

Toby wrote:

It is, but sadly any soil in the area is topped with a thick layer
of concrete right up to the edge of the house.

Cut back concrete along the wall, dig trench, fill to brim with coarse
gravel.


This doesn't sound like a diy job. Not if you mean the application of one
of those terrifying massive grinders that pavement operatives use in busy
shopping centres to cut curbstones!


These are hirable and rather fun.

How wide does such a trench need to be
anyway?


depends on what teh surface is, if clay, quie big - maybe half a meter wide.

In article ,
JK wrote:
The Natural Philosopher wrote:
JK wrote:


I'd say injection is the way to go frankly. My previous house was
rotten
with damp, some of which was rising. Where it had been injected it did
actually solbve th eproblem (suffolk clay)...sadly hu=ge areas on
internal walls and in partucular the fireplace couldn't be injected,
and
that was where the rot was the worst, and the effloresence..

Well I guess I could try injection first. Tell me, is it possible to inject
on the inside? The lowest point on the outside would be around the top of
the skirting board on the inside, so I'm guessing I'd still have a proble.
Of course that problem would perhaps be behind the skirting so out of
sight...

And there-in lies your problem. You may be avble to get rid of your damp
by lowering the outside gound level to prevent rain from splashing up te
walls. I've done this for my house where the old slate damp proof course
was only a few inches above the outside ground level.

1 Cut back the concrete path 6" from the wall
2 dug out some soil and replaced with pea shingle.
3 ground now 6-8" below dpc

The inside floor level was above the damp course so when replacing the
tile on mud floors the damp proof membrane was looped down below the dpc
and then up to the level between the sand and polystyrene insulation.

There's a lot of discussion about whether injected DPCs work and whether
it's better to spend time changing ground levels etc. Obviously make sure
that gutter leaks etc. aren't causing the damp. And check to see if you
already have a DPC. My house it 150 years old and has a slate one,
although it took a while to find it.

Search googlegroups for past postings on DPCs.

Neil

In message , JK
writes
The Natural Philosopher wrote:
JK wrote:


I'd say injection is the way to go frankly. My previous house was
rotten
with damp, some of which was rising. Where it had been injected it did
actually solbve th eproblem (suffolk clay)...sadly hu=ge areas on
internal walls and in partucular the fireplace couldn't be injected,
and
that was where the rot was the worst, and the effloresence..

Well I guess I could try injection first. Tell me, is it possible to inject
on the inside? The lowest point on the outside would be around the top of
the skirting board on the inside, so I'm guessing I'd still have a proble.
Of course that problem would perhaps be behind the skirting so out of
sight...




What you should do is lower the outside level to well below your
floor/joists, then inject in the 3rd brick above the new level.


--
Richard Faulkner

JK wrote:

This doesn't sound like a diy job. Not if you mean the application
of one of those terrifying massive grinders that pavement operatives
use in busy shopping centres to cut curbstones! How wide does such a
trench need to be anyway?

More of a spring job than a winter one but not too arduous. You'd be
surprised how thin the concrete turns out to be, maybe only 1" over rubble,
especially if it is an old house. Like Niel says a 6" from the wall is good,
the depth is dependant on your own circumstances. An angle grinder won't go
through the whole thickness but will provide a score line which will
encourage the concrete to crack along it. USe a variety of hammers, drills,
chisels, picks, levers etc to create the channel.

New houses with paving around them often have a deep fill of pea shingle or
gravel around the walls.

--
Toby.

'One day son, all this will be finished'

The Natural Philosopher: JK wrote: Toby wrote: N. Thornton
wrote:

Cut back concrete along the wall, dig trench, fill to brim with
coarse
gravel.

This doesn't sound like a diy job. Not if you mean the application of one
of those terrifying massive grinders that pavement operatives use in busy
shopping centres to cut curbstones!

It is. You need indirectly vented goggles, tough gloves, and
prefrerably tough boots, thats all. Scrwefix sell 9" angle grinders
for what, £29? And treat with care

If you know the concretes only 1" thick even a 4" angle grinder would
do.


How wide does such a trench need to be
anyway?

depends on what teh surface is, if clay, quie big - maybe half a meter wide.

I'm not clear why 0.5m was suggested. As far as I can see all you need
is to keep the stuff off the wall and allow a bit of drainage, so 6"
should do it.

Hopefully the concrete is sloped very fractionally away from the
house, as it ought to be.


Indeed the concrete outside is at a slightly higher level than the floor
inside,

problem located. The solution to the problem is to solve the problem.
Ie lower the concrete level outside. Since that will give you a lower
water collecting area you will also need to add a drain to prevent
water collection.

You're right, but it's not an option. I need some kind of remedial
treatment for a problem created by bad design. Breaking up 10 sq metres of
concrete, digging out, installing drains is just too much, partly from a
cost point of view and partly because any mess has to be carted through the
flat to get it away.

1. You dont need to do 10m2
2. You probably dont need drains, but I dont have the knowledge on
that.
3. rubble sacks were made for carting junk through houses.
4. What else are you going to do?

You could try lifting the floor if wood, injecting every brick upto 6"
above ground, and injecting the floor if concrete, but it may or may
not work. I wouldnt be too confident.

The absolute minimum you could do would be to use a dehumidifier.
Drying the air will increase the rate at which the wall dries off.
Theres a chance that might make things passable.


Regards, NT

OK, Thanks to everyone for some really helpful advice. I'm coming round to
the idea of cutting a trench and then maybe injecting if that doesn't solve
it. I already have a small angle grinder so I guess I need to stop being so
wussy. Something to do over christmas anyway!

Thanks again,

John

JK wrote:

OK, Thanks to everyone for some really helpful advice. I'm coming round to
the idea of cutting a trench and then maybe injecting if that doesn't solve
it. I already have a small angle grinder so I guess I need to stop being so
wussy. Something to do over christmas anyway!



The thinh youi need for most concrete is indeed a specialised form of
angle grinder. I hired one some time ago to cut therough a concrete path
and install underground incoming mains cable.

I hired it and its 110V trnsformner for a couple of days. It tookk me
finally once i got teh hang of it about 2 hours to cut a 4 ft long
section out of 4-6" thick concrete. No way an anggle grinder of the
hobby variety would do that.

No special safety equipment is needed apart from some eye protection. I
wera glasses thes days anyway and they were enough.


Thanks again,

John

On Thu, 4 Dec 2003 20:16:17 -0000, "Toby"
wrote:

JK wrote:

This doesn't sound like a diy job. Not if you mean the application
of one of those terrifying massive grinders that pavement operatives
use in busy shopping centres to cut curbstones! How wide does such a
trench need to be anyway?

More of a spring job than a winter one but not too arduous. You'd be
surprised how thin the concrete turns out to be, maybe only 1" over rubble,
especially if it is an old house. Like Niel says a 6" from the wall is good,
the depth is dependant on your own circumstances. An angle grinder won't go
through the whole thickness but will provide a score line which will
encourage the concrete to crack along it. USe a variety of hammers, drills,
chisels, picks, levers etc to create the channel.

And most importantly, remember to think of people you don't like as
you're doing the hammering ))

When I was knocking the bathroom into an adjacent bedroom I made the
job much more pleasurable by picturing all the managers at work that
were making my life hell!
--
cheers,

witchy/binarydinosaurs