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
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.
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.
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. Any tips?
Thanks
John
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.
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 :-)
Yes, but it may be cold because its damp already
Run that past me again?
Mmm.
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.
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.
J
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? J
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..
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
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 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.
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.
The solution to the problem is to solve the problem, not to do things that dont solve the problem.
Regards, NT
Cut back concrete along the wall, dig trench, fill to brim with coarse gravel.
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
A colonial drain.
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?
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.
These are hirable and rather fun.
How wide does such a trench need to be
depends on what teh surface is, if clay, quie big - maybe half a meter wide.
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 dpcThe 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
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