Damp on bottom of wall?

paperclap

Hi all,

Literally just about to put some skirting board down in this room, and I notice a handful of damp spots on the bottom of one (external) wall.

This is the wall behind the bed. We’d noticed a bit of mould on the floor too. Just scrubbed it off. Had noticed a bit of mould on the underside of the mattress last year but put it down to it just being winter.

We’ve got a new roof, so can’t see it being a roof leak.

This external wall does get hit by a lot of rain, but even still. Pointing is all okay.

It’s been raining all day today. But before this, not much rain at all, and a lot of nice weather.

Could it be as simple as condensation on the coldest part of the wall where very little airflow happens?

How can I fix this? Wanting to put MDF skirting board down tomorrow! Agh!

paperclap

UPDATE

In the space of about 30 minutes, it’s almost visibly dried… so I think it is just a case of a little condensation due to lack of airflow?

However, given it’s MDF skirting I’m putting down, I don’t want to run the risk of damage to the skirting.

Found this tin in the shed. Is it worth putting a coat of this stuff on to the wall prior to fixing the skirting?

It obviously doesn’t “fix” any damp, if there was of course an issue of damp there… but perhaps it will create a seal of sorts between a potentially cold wall and the back of the MDF skirting?

FIREmenow

Hiya, where in your house is this room and what is the grey stuff on the wall made of? Sand and cement? How old is your house and is the wall solid or cavity? 

Depending on those answers, it could be surface condensation on a cold wall, or damp trying to escape, particularly if the bottom of the wall is below ground level outside. Blocked up air bricks could also be reducing airflow around the joists below forcing the moisture upwards. 

As you say, damp blocker won't solve the problem, it's like covering it with a plastic bag. - If it's condensation then the wall, and therefore the skirting board, will still be as cold, if it's moisture trying to get out it will keep traveling to a point beyond the damp blocker where it can get out. If it's likely to be an ongoing problem then damp proof/prime the back and underside of your skirting board - not the wall so it can still 'breath'.

Check the humidity in the room and try to improve ventilation. Drying washing, wet towels and just breathing whilst asleep creates a lot of water vapour that needs to get out. Go out and check what is happening to the outside wall on a rainy day - gutters leaking, slipped tiles or poor leadwork good be quietly letting rain in.

Those moisture meters are not meant for measuring moisture in walls, and salts present in the wall make them unreliable.

ThisIsWeird

The answers to Fmenow's Q's, please.
Plus, how long have you lived here? Was that 'cement layer' put there by the previous owner?
I have to say that condensation is surely very unlikely in our current climate? And if you were to suffer cond in that room, I'd expect it to be more in a corner.
I therefore suspect this to be either 'penetrating', or 'rising', and that mortar to be a failed attempt at sorting it. But I obviously don't know.
You can theoretically seal that visible mortar strip to prevent damp coming through, by using a proper tanking slurry, but my concern would be what's happening below floor level.
Is that laminate flooring? Relatively easy to lift along there to see what's going on below? Is that a suspended floor or solid. And, as asked, solid or cavity?

stuart45

You can check the odds of condensation forming with a hydrometer/thermometer and a surface thermometer. Any surface below the dew point is likely to have condensation forming on it. 
It's possible that mortar droppings in the cavity are above the DPC, although this is less likely in a bungalow.

paperclap

Back bedroom.

1950s bungalow, made up of brick and mortar, cavity wall, with cavity insulation. No joists. Two air bricks on the other side (outside) of this wall. 

Outside of this wall is a car port with a concrete ground.

To the right of this wall, there is obviously another external wall… but all grass. So perhaps better drainage?

Last night I put a coat of that damp seal on. Says water can escape if there is any there. Didn’t want to to do it today and wait 4 hours for it to dry before I could put skirting down.

It was absolutely pouring it down last night from about midnight until about 5am or whenever. So much so that it woke me up. I’ve just gone right now to check it again, and no damp spots. Whereas before when damp spots were there, the rain was very light. Plus, when we did move the bed away from the wall, those damp spots visibly went within an hour. These damp spots are only behind the bed, too… of which does always have a load of boxes for storage under it. No damp where the bedside tables are (which are open).

Also for what it’s worth, the previous owner when repointing, repointed over the damp course outside. No doubt this is bad practice as surely you’re bridging below to upper brick then? But we’ve not had this problem that I can see elsewhere. But then again, all the other external walls (inside) are either covered up by tiles in the bathroom, wooden cladding in the kitchen, have grass (for better drainage) or have a downward slope (which acts as better drainage).

stuart45

Bridging the DPC on the external skin on a cavity wall isn't the same issue as with a solid wall. It sounds likely to be condensation, although CWI occasionally causes internal damp problems.

paperclap

Photos from outside. 

You can see where the previous donut has crossed the DPC with the pointing. You can see efflorescence both above and below that DPC. Concrete car port. Directly behind me there is a rainwater drain (no, don’t believe this to be the cause), so there is a form of drainage.

But the same situation is on the other wall too (with the window above). Bridged DPC. Efflorescence. But grass for drainage.

In fact, the whole house has had its DPC bridged, bar the recently built (15-20 year old) conservatory. That too has efflorescence.

The DPC is under the mortar line that is just below the air bricks.

stuart45

The external DPC is often bridged, even when first built. Although in theory the NHBC want it 5mm each side of the brick, it's often set back slightly so it's virtually invisible and when jointed up you can't see it. 

paperclap

Okay, great. So the bridged DPC hopefully isn’t the issue here then.

The whole house has CWI, and never had issues with the walls being able to “breathe” elsewhere. Never spotted any peeling paint, etc.

Like I said in my original post, we’d had mould on the underside of the mattress (saw it last winter), bit of light mould on the laminate flooring in that one section, and even just spotted two very tiny spots of peeling paint on our almighty IKEA wooden bed. Lots of boxes under that bed, which no doubt isn’t helping airflow.

Don’t want to just tell myself the easy answer of “it’s condensation, just move stuff away from the wall”… but, it does sound like that condensation may be the case?

Eldi_Dos

Have you considered cutting back the concrete by 150/200 mm digging out and putting gravel in its place.