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
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.
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
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.
Can the injection not be done from the outside?
I just want to make sure I know where it comes from before I take measures.
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
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
I assume you don't have/do anything silly, like unflued gas heating or
constantly drying clothes indoors?
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?
No, I think you're right. The plaster shows years of tide marks so it does
look like it's coming from the ground.
Nothing like that unfortunately.
Anyone know a reputable damp specialist in North London? Don't laugh.
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.
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.
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
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 :-)
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.
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.
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?
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..
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
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
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.
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
The solution to the problem is to solve the problem, not to do things
that dont solve the problem.
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
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