1930s semi. Damp downstairs chimney breasts

Discussion in 'Builders' Talk' started by Monty_is_chonky, Sep 24, 2021.

  1. Monty_is_chonky

    Monty_is_chonky New Member

    I have a 1930s semi - chimney is capped with one cowl remaining (presume for ventilation?)

    I keep getting damp in the front room and back room chimney breasts. Front room one has been ongoing for a year and the back room damp has just appeared.

    Front room had a vent behind the electric file, backroom is fully boarded over but no sign of damp or water on the boarding at the top.

    I've been into the attic and the left hand side of the stack (leading to the back room) has irregular patches of wet on the mortar.

    The chimney was not long ago dashed. Not sure if its relevant but used to have an aerial on the stack that has now been removed so this has left a patch where it was dashed around.

    I'm clueless but keen. Is it as simple as adding a vent into the back room? Has the chimney been incorrectly capped? (Literally covered in cement with one stack/cowl left on the back side).

    Pics attached. Its minor but driving me mad and I don't want it to get worse and create an issue for my baby.

    Note: only have damp downstairs, upstairs chimney breasts are 100% fine

    Attached Files:

  2. GRH

    GRH Member

    I suppose it was 'dashed' with cement render - perhaps it should have been lime so the bricks could breath? The picture looks like condensation working its way through, and possibly running down inside the chimney flue. It could be the ventilation - you may have a vent downstairs, but if the air can't escape, neither can the water vapour held in it, so it would condense on the brickwork. I am pretty sure there should be a flu ventilator on the stack that lets the air and moisture out and at the same time prevents rain getting in.
  3. Monty_is_chonky

    Monty_is_chonky New Member

    Thanks for the reply. There is one on the stack, should have been clearer. So frustrating, spent so much on the house and this is one of those recurring issues that I just can't fix. Going to get up on the roof and look at the flashing in case that is the issue and add a vent to the backroom.
  4. Mr Rusty

    Mr Rusty Screwfix Select

    I've had a similar challenge. My own problem is salt poisoned bricks caused by the reactions of combustion products with construction materials. Downstairs worse because that's where most of the fires were.

    The salts are hygroscopic, attracting moisture out of the room causing crystals and "dampness" to grow. If you don't want to strip back to brick and use salt resistant materials, try this.

    Remove all existing paint/paper to plaster. Fill any dints and allow to dry for a little while exposed. If anything "grows" sand it off. Paint the area with a dampseal paint like ronseal dampseal. This isn't to keep damp in, but to create a barrier to stop room moisture getting to the salts. Redecorate.

    I have had 95% success doing this.
    Monty_is_chonky likes this.
  5. Monty_is_chonky

    Monty_is_chonky New Member

    Funnily enough, this is exactly what I did in the living room. That is 100% the issue in there. Its starting to fail a little now and the paint is getting dark (but not damp) where i fixed it so will need redoing with perhaps better quality damp seal.

    The back room i am not sure if its the same. The damp patches seem more like "proper" damp. Dark patches, rather than the salt/crystals we had in the living room. Pics of back room damp attached for clarity.

    Attached Files:

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