Damp patches in new plaster

[briankorteling]

Hi, we had a wall re-rendered and platered about 2 months ago and there are still some quite large damp patches in the plaster. The house is an old brick terrace and the wall in question is an exterior wall that has been painted and repointed with concrete which I understand from the plasterer is the wrong thing to do as the wall can no longer breath. I intend to insert an air brick into the wall in question but was wandering if anyone has any other ideas on how to dry it out.

 

[PrenticeBoyofDerry]

What areas is it effecting ie height up wall?
What is on the external wall ie is it above ground level?

 

[trowelmonkey1]

so your walls are solid and have no cavity?

any vents/airbricks in the walls should never be covered, the house needs the movement of air if you have no cavity, so if one has been covered then you should uncover it or put one back in.

that aside the patches need some thought, where is the damp coming from?

bridged DPC outside maybe? or rising damp? where on the wall is it exactly?

 

[joinerjohn]

Are you sue that these are damp patches?? Sometimes plaster can dry in various shades depending on whats underneath the plaster. Even could be due to the plasterer mixing a different batch number of the same plaster.

 

[Richard C]

Sometimes plaster can dry in various shades depending on whats underneath the plaster.

If it's still showing damp after 2 months, then there's a problem.

Even could be due to the plasterer mixing a different batch number of the same plaster.

It might go off at slightly different rates but Ive never heard that one before


A few other questions for the OP;

Hi, we had a wall re-rendered and platered about 2 months ago

so is that render & plaster on the inside only or was the outside also rendered? What type of render was used?

The house is an old brick terrace and the wall in question is an exterior wall

As previously asked, is it a solid brick or cavity wall?

that has been painted and repointed with concrete

Repainted with what & where?

What’s been repointed the exterior brickwork? Why do you think that's relevant to the damp problem?

which I understand from the plasterer is the wrong thing to do as the wall can no longer breath.

Did he say why it was the wrong thing to do?

I intend to insert an air brick into the wall in question but was wandering if anyone has any other ideas on how to dry it out.

Can you explain why you think an air brick will help cure the problem?

 

[briankorteling]

Thanks for the feedback everyone. The room is on the first floor and the patches are at various heights one is low under a window, one around waist height and the other around head height. The window isn't leaking and is a newish UPVC. The roof was leaking but has been fixed and this was the source of the damp and the reason for re-plastering in the first place.

I think that the wall just hadn't dried out properly and there is still damp patches trying to dry out. The real question is if paint will stay on top of these patches is it ok to paint and see what happens?

The patches are dry to the touch and I have drilled a few holes in places that i will fill later in order to help the wall dry, any other advice or ideas?

 

[briankorteling]

To answer other questions, the wall has a cavity i beleive and there is an external air brick.

I also watched the plasterer at work and as it is only a small wall in a box room I know that he used the one bag of plaster so I'm sure that they are caused by damp.

Thanks again

 

[briankorteling]

Some more points to answer. The wall was rendered and plastered on the inside not outside but the wall in question has an exterior face if you see what i mean. The exterior of this wall is unrendered but has been repointed and painted. This i have been told will restrict the old red bri cks breathing as they should and prevent water evaporating. The interior side of this wall was lime rendered and the mortor was lime also I think so the plasterer used a mix of multi finish with a little lime on the top coat, the lime i was told would help the wall breath a little.

 

[briankorteling]

I was told by the plasterer that an external airbrick would help the building breath as tnher exterior face of this has effectively been sealed by paint and concrete. Right or Wrong?

 

[PrenticeBoyofDerry]

I'd be supprised if it has taken 2 months to dry out under normal conditions any signs of efflorescence?

What condition are in the location of this wall, is it heated and dry?
are you sure the original problem was resolved?

 

[JohnD]

. The roof was leaking but has been fixed and this was the source of the damp and the reason for re-plastering in the first place.

If the brickwork was actually wet, due to a leak, it can take many months to dry out. Some bricks may be harder or less absorbent than others (especially in an old terraced house where the builders may have used cheap bricks), and often you can see the pattern of bricks showing through the plaster in damp patches. Are the damp patches showing as a chocolate colour, and the dry plaster pale pink?

Usually the way to dry out is by opening the windows and giving it plenty of ventilation, but in this weather I expect you are reluctant, and anyway, it is so cold that there will not be much drying, you might even get condensation if the wall is very cold. If the window has a trickle vent, leave it open. Once the frost has gone, ventilate it more. When you redecorate this room, use a Matt Emulsion (non-vinyl) for at least a year as this lets it dry out best. Dulux Trade Supermatt is good.

When you say an old terraced house with lime plaster, I picture something from about 1900. In this case it will not be a cavity wall. Measure the thickness of the wall at a door or window opening, if it is nine inches plus plaster, it is solid. People who like old buildings usually say that if they were built with soft bricks and lime mortar, you should not use cement as it is too hard and not so porous. I don't know much about that.

Some photos of the wall (inside and out) will help.

 

[briankorteling]

The majority of the wall is dry i.e. pale pink but there are these darker patches. i wouldn't say that they are chocolate brown more like a good tan with a bit of sunburn if that makes sense.

I have painted over these areas with a watered down mix of matt emulsion and initially this stayed wet and ran straight of these areas but after giving it another coat with this mixture it appears to be sticking and the paint has dried so maybe it's ok to paint, which is what I need to do whilst I have the time thanks to the weather.

I'm 99 percent sure that the problem with the leak has been solved (st least i hope so) and have no way of checking this until it rains, but as i said it has been drying for 2 months or more in which time there has been some pretty heavy rain and the patches haven't grown they just haven't shrunk very much.

 

[phil8340]

Hi

I would try putting a airbrick in the external, when you are doing this try cleaning out the cavity at the same time. The mortar from building and over time it drop to the bottom of the wall, this then breaches the cavity.

Hope it help, good luck