Found cause of damp problem..what do I do now?

[farmo]

Hi all,

I believe I've found why the wall in my spare bedroom is damp (If my measurements are accurate), it seems the bottom of the skirting board/floor is lower than the DPC!
If this is correct what can I do?
Please see picture below, sorry about the quality/size.


View media item 26355

 

[r896neo]

If this is the case it it not necessarily a mistake but the dpm from under the floor must come up to at least the level of the dpc in the wall and preferably over it by an inch.

Having that rubble/debris in your cavity will not help the situation at all but the wall dpm and floor dpm need to meet as i described. The other possibility is that the dpm is brought up the wall and lapped into the same joint the dpc is in and that method would also be correct.

 

[JohnD]

concrete floor or wooden?

 

[r896neo]

good point.

 

[farmo]

concrete floor or wooden?

Concrete floor.

r896neo-
I don't think the wall dpm and floor dpm meet as you described (my new extension is though) as I have knocked a hole in the wall and couldn't feel it, just lots of rubble as far as I can reach each either way.

Is this a modern technique as the house was (badly) built in the late 60's?

I get what you mean about the levels, the floor dpm is much lower than the wall because the wall dpm is almost level with the middle of the skirting!
I'm really confused as to what to do.
Do I just need to get the rubble out?

 

[JohnD]

where is the external ground level in relation to the DPC?

look for any particular source of damp, such as a leaking pipe in the floor, or a dripping gutter or raised ground level outside. there is often a combination of causes when you get noticable damp; if it is slight and the room is well ventilated, it can usually just evaporate away. sometimes water can drip from above, e.g. a bathroom

is the rubble in the cavity bits of mortar and broken brick, or fine material as well? how damp does it look and feel? when you pull it out, do you notice it getting dryer and lighter when expose to the air?

can you lay your hands on an aquavac or similar? I have had fair results removing small rubble by poking a strong vac hose into a cavity, and it will also grab pieces of brick that are too big to pass down the hose.

 

[farmo]

The ground is about 3 courses below dpc, there is a down pipe in the corner which I have dug out to check and the soil is dry all around it.

Its a bungalow, nothing above, had a new roof 2 years ago when we extended on the back & south side side. Has been a problem since we moved in 10 years ago.

I will pull some more rubble out tonight and check for dampness, I didn't notice any initally but I think the problem with damp is escilated during the winter as its a north facing wall with low sun light this particular corner.

Great idea with the vac, I could hire a industrial one and try it.

I can't thing what else it could be, the floor seems dry (tested by sticking down clear polythene and left overnight) but the grippers rods are rusty!

 

[JohnD]

try the polythene taped tightly to the wall for a few days, in case it is condensation. If so, ventilation is the best cure.

 

[r896neo]

As John says try and rule out condensation first.

The dpm-dpc junction i mentioned is pretty fundamental building practise. In reality the vast majority of concrete floors finish pretty close to the dpc and are generally only significantly below it with stepped dpc on sloping sites or in extensions/ conversions.

If you think about it a dpm stops water rising into your concrete slab. A dpc also stops water rising up the walls. However if, as in your case, the dpc in the walls is above the floor so water, though in very small amounts, can travel up the wall to the impervious dpc where it stops then it seeps sideways though the wall where it normally hits a dpm turned up the side of the concrete floor but in your case that dpm is not there so it just seeps into the room.

That make sense?

because your cavity is bunged up water chooses the easiest path and goes into the room so if you clear the cavity you give the water a choice to go one of two ways once it hits the dpc. Then you can paint on some liquid damproofing on the inside which will force the water to choose the easy route into the new clear cavity. Hopefully

 

[farmo]

Thanks guys,

Totally understand what you mean.

I didn't have a chance to do much more investigating tonight as I finished work late.....again!
I did however tape the polythene to the wall and had a root about in the cavity and discovered a brick tie covered in cement which was about level with the floor, obviously this could be the/a cause right? Why put a brick tie in this low?
I guess I need to rule this out further along the wall too now, which will be a right pain in the butt and clear rubble from the cavity.

One thing I should have told you (sorry) is during the winter we do have condensation on the windows, they are about 5 years old & upvc but have a tendency to mould up on the rubber bits, we guessed it was because the room was damp and not neccessarily because of poor ventilation. Also we have a air brick along this wall but looking at all the cr*p in the cavity it's probably not effective.
As i'm writing this I think i'm answering some of my own questions!!
Thanks again, will keep you posted.

 

[JohnD]

some good stuff in here

http://www.diynot.com/wiki/building:condensation_in_houses

 

[maltaron]

I would suspect that as this bungalow was built in the 60's the floors were originally timber. It was quite normal to put the DPC on the inside skin 2 courses lower than the outside with the floor joists sitting on the DPC. The comments regarding a blocked up airbrick makes me suspect that the timber floor had dry rot and was replaced with concrete without a membrane or proper DPC design. The ideal course of action would be to put a DP membrane over the concrete and lay a 40mm granolithic screen over it, tying the DP membrane to the dpc in the wall. (you do not show a DPC in the internal wall but I would think there is one) This would of course be a major job as doors will need reducing or the frames raised.