Airbrick causing damp?

[erikwoolf]

Could the outside air brick cause damp on the inside?
This is a newly plastered wall with lime. Previously everything has been hacked back to the brick (last year) was left to dry and then plastered with lime last summer.
The wall has damp patches, the biggest one corresponds to where the air brick is on the outside. Could that be causing the big damp patch on the inside?

 

[erikwoolf]

Any ideas if the two could be related??

 

[aockenden]

Was your aggregate in the lime plaster well washed? I’ve heard from others, and seen some possible evidence of this in my own lime work, that salty unwashed aggregates can readily soak-up and hold onto moisture in the air. I’m not 100% decided if I believe this story yet, but it’s often repeated in lime plastering info sources.

My thought was that maybe moist air is blasting in from outside, through the air brick and salts in the aggregate are soaking up that moisture from the air and having trouble releasing it. Have you seen any salt deposits being deposited on the surface of the lime plaster?

 

[jamest]

Another thought - given the bond, that looks to be a solid wall, one brick length thick (9"), is that right? If it is, then are those air-bricks above the interior floor level? You say that they are where the dark patch is on the plaster, implying that they are above the floor level. If that is the case, then they should be removed because (1) water could get through the air bricks and dampen whatever is on the inside of them and (2) will produce a colder spot on the interior wall surface, which will attract condensation. Either or both of these could produce damp areas on the interior plaster.

 

[Lime]

The next time it is raining, go outside and examine the run-off from the window cill.
Often the rain will run-off on one side more that the other and dampen that wall.

 

[Mummy will fix it]

Another thought - given the bond, that looks to be a solid wall, one brick length thick (9"), is that right? If it is, then are those air-bricks above the interior floor level? You say that they are where the dark patch is on the plaster, implying that they are above the floor level. If that is the case, then they should be removed because (1) water could get through the air bricks and dampen whatever is on the inside of them and (2) will produce a colder spot on the interior wall surface, which will attract condensation. Either or both of these could produce damp areas on the interior plaster.

This is right. The air bricks are meant to provide ventilation under the floorboards. Even if positioned correctly, it’s not a great idea to block them up. I’m trying to work out how you’ve ended up with an air brick in the middle of your wall!

 

[fixerupperer]

Is the material around the air bricks cement? It’s quite a large patch there and seems to be dotted about in other areas nearby as well. It’s really porous so any moisture within that cement only has one way to go and that’s sadly out through the breathable lime walls.

I’d also echo what others have said about the air bricks being too high and perhaps relocating lower to be in line with underneath the floorboards, and fixing in place with a material with lime in the mix could help.

I can’t tell for certain from your picture, but if the lime plaster goes all the way down under your floorboards it may well be too close to ground level and soaking up moisture from the outside that way. I was always told plaster should end just above your floorboards. The gap would be covered with skirting so you’d never know.