Damp On Wall

[80's Owl]

I'm currently renovating a house for rental, its a Victorian terrace built in the 1870's. A damp patch about 250mm has appeared above the skirting board on one wall, the wall is external with no clear signs of damp on the outside, it's not an exposed wall as it's on in a gennel (as we say 'oop North) below is a basement with no obvious signs of damp in there either.

 

I doubt we'll ever find where its comong from (rising damp has been mentioned) but is there a solution to hold it back?

[Square Feet]

You can get a damp patch like that from condensation if there is furniture up against the wall which is restricting the airflow. The gennel (vennel in Scotland) will be very cold so insulating that wall should sort the issue. You'd need to strap and line the wall with an airgap and then use insulated plasterboard. In Scotland there are government funded schemes to get this done - I am getting just this done on a similar property just now and the vennel wall counts as an external wall for the insulation grant. 

 

Otherwise using a damp proof membrane like this one should keep the damp at bay, but the condensation issue might still occur as there is less insulation value in the membrane. You then have to plaster over the top.

 

Slapping damp-blocking paint over it is a temporary bodge that will really only work if you intend to sell the property very soon.

[jayc89]

Presumably solid wall construction? What's been used to point/render the wall in that area? 

[80's Owl]

26 minutes ago, jayc89 said:

Presumably solid wall construction? What's been used to point/render the wall in that area? 

 

Its exposed brick on the outside, plaster inside.

[80's Owl]

1 hour ago, Square Feet said:

You can get a damp patch like that from condensation if there is furniture up against the wall which is restricting the airflow. The gennel (vennel in Scotland) will be very cold so insulating that wall should sort the issue. You'd need to strap and line the wall with an airgap and then use insulated plasterboard. In Scotland there are government funded schemes to get this done - I am getting just this done on a similar property just now and the vennel wall counts as an external wall for the insulation grant. 

 

Otherwise using a damp proof membrane like this one should keep the damp at bay, but the condensation issue might still occur as there is less insulation value in the membrane. You then have to plaster over the top.

 

Slapping damp-blocking paint over it is a temporary bodge that will really only work if you intend to sell the property very soon.

 

I assume for this you hack the plaster off, put this on then replaster over?

[jayc89]

1 minute ago, 80's Owl said:

 

Its exposed brick on the outside, plaster inside.

 

What's it pointed with; lime or cement? 

[80's Owl]

2 minutes ago, jayc89 said:

 

What's it pointed with; lime or cement? 

 

Not 100% but I doubt it will be lime.

[jayc89]

7 minutes ago, 80's Owl said:

 

Not 100% but I doubt it will be lime.

 

That would be my starting point. It needs to be lime. If you start putting anything impermeable on the internal face you'll just trap any moisture in there; it has to be able to escape one way or another. 

Keep the room well ventilated until you manage to find the source. 

[80's Owl]

11 minutes ago, jayc89 said:

 

That would be my starting point. It needs to be lime. If you start putting anything impermeable on the internal face you'll just trap any moisture in there; it has to be able to escape one way or another. 

Keep the room well ventilated until you manage to find the source. 

 

So you're suggesting raking out and repointing in lime?

[jayc89]

3 hours ago, 80's Owl said:

 

So you're suggesting raking out and repointing in lime?

 

It would certainly be beneficial, but if the bricks aren't visibly darker in that area, it's unlikely that the mortar is causing your current problems. 

[80's Owl]

5 minutes ago, jayc89 said:

 

It would certainly be beneficial, but if the bricks aren't visibly darker in that area, it's unlikely that the mortar is causing your current problems. 

 

I don't think it is as they are not subject to any direct weather, rainwater etc.

[Square Feet]

On 11/12/2023 at 12:20, 80's Owl said:

 

I assume for this you hack the plaster off, put this on then replaster over?

That's what I did yes. Any moisture that is trapped in the bricks should then exit outwards over time rather than wicking inwards on the plaster.

[Susie]

Have you checked your gutters are empty no blockages. We have a lot of trees near us the wind either empties the gutters or fills them with leaves. 
also check neighbors are not splashing your way.