Wet patches on walls.

[Jim]

I have a house (victorian terrace) that has several wet patches on the walls downstairs (kitchen and through dining room)

These patches come and go, but are always in the same place.

1) In the kitchen around the edge of the tiled splashback, and under the work surface. 2) On the chimney breast 3) On the wall next to the chimney breast (not wet but can seen a change in colour on the walls that comes and goes)

The patches appear 2 metres or higher on the walls. I have previously removed the plaster and replastered the area on the chimney breast (2), and fitted an airbrick to the breast.

The wall next to the chimney breast backs onto the shared passage, therefore the wall should be quite dry, and unlikey to be penetrating damp. I also understand that it cannot be rising damp, and there is no dampness at floor level, but higher than 1m.

The wall in the kitchen is similar not an outside wall, and I can see no reason for moisture penetration.

The house is fully double glazed, so the walls may be the cold spots. Could this be caused by condensation? particulary as it directly adjoins the kitchen. What would be the recommended methods to resolve this? Would a dehumidifier be useful in these circumstances. Any other suggestions?

[George]

Are the wall/s adjoining walls or are they gable end walls?

When you say "come and go" have you noticed any particular instance of them reappearing? ie they appear when it rains,they appear when your're cooking or after? Usually the problem can be narrowed down if you notice the conditions the damp appears. For instance a blocked chimney after a downfall some of the rain could be getting down it and settling in/on the blockage then seep through the brickwork,if you don't have a cowling on the chimney stack? then fit one,Im not saying this is the likely cause but no one can give a definate answer to the problem without actually seeing it when it occurs.

[Jim]

The walls are adjoining walls (as mentioned the one side backs onto the passage and is therefore sheltered. I havent yet found a pattern. There were damp patches whilst the house was unoccupied, so it is not purely down to cooking etc. However having said that, Dampness does seem worse after cooking, but my feeling is that this area is already damp, and so may be attracting any additonal humidity.

Are the wall/s adjoining walls or are they gable end walls?

[The Natural Philosopher]

[mail]

In a word -hygroscopicity

Hygroscopic salts are contaminating the plaster and it should be removed and replaced with a non-gypsum preferably sand cement with salt retardant additive and SBR and a water proofer. If it is not TOO bad and you want to be a cheapskate you could try painting it with a metallic OS paint but I dont recommend it

Cause on the chimney is SO2 from fossil fuels going to sulphur trioxide to sulphous acid and then sulphates

elsewhere dont know but could be water entry over the years bringing in salts

Could be defective sand in original mix!

IF condensation on Cold spots that would only be a contributory issue as hygroscopic salts reduce themal insulation

Would not dehumidify suggest getting rid of water in the first place as better Chris

[Pete C]

Hi,

Is the fireplace blocked off, and is the airbrick on the inside or outside?

cheers, Pete.

[meow2222]

Ask people that know the subject, this is a bit of a blind spot on uksiy