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Sudden damp patch on wall

Discussion in 'Building' started by profile50e, 2 Nov 2020.

  1. profile50e

    profile50e

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    Hi all,

    I've got a damp patch that suddenly appeared in the living room after some intense rainfall this week. It was quite damp to the touch on the inside but no obvious entry point outdoors.

    I have a suspicion that the entry point might be the window frame, where the sealant has aged and there are some visible openings. Any thoughts?

    Cheers.
     

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  3. profile50e

    profile50e

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    + view of window frame further up - there seems to be a bit of a gap further up too..
     

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  4. JohnD

    JohnD

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    where do you think the DPC is, in the wall?

    Is there any sign of sinking or repairs around that gulley?

    How far is the grille, below the surface of the new paving bricks?

    Does the paving slope towards the house, or away from it?

    Stand back and take a wider pic please, including the gutters above and the aitbricks in the wall.

    can you take a wider photograph of the wall with the damp patch inside?

    Was the black paint round the bottom of the wall an attempt to hide damp?
     
    Last edited: 2 Nov 2020
  5. profile50e

    profile50e

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    Hi - regarding the dpc, all I know is that the previous owners used Rentokil to remediate that entire front wall in 2011. I don't have much paperwork other than a brief survey from Rentokil from that time. My own surveyor from around 2015 (when I bought the house) was happy with the work and thought it had been treated chemically. The Rentokil report talks about installation of a new damp course.

    Gulley looks ok, but then I did find some failed render right behind the pipes - is that worth investigating further? When it rains, the water does clear quickly and never sits at that gulley though.

    The grille at the front is clear and I've attached a picture, it's above the surface of the drive.

    Paving slopes away gradually at first and then more aggressively. It's a few degrees next to the house.

    The black paint - no it was re-rendered and painted a couple of years ago as part of the front of house re-decoration. There's no sign of damp in the render that I can see.

    One other thing I noticed is that the driveway gets pretty much up to the wall in the gulley area. Around the bay window there is a gap between paving and render.

    Thanks.
     

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  7. profile50e

    profile50e

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    + inside view
     

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  8. JohnD

    JohnD

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    looking at the paving and the black paint at the base of the wall, it seems that the paving is higher around the (later addition?) porch than round the bay window. The ground seems to slope down to the bay window. If you tip a bucket of water on the paving, which way does it run? If water puddles by the air brick it can get inside. If it puddles by the wall it will make the wall wet.

    Where the rendered plinth is higher than the paving, it looks like the ground has sunk, taking the paving down. A common cause of this is a broken drain washing the soil away.

    i can't see into your gulley. I am expecting that it will be below ground level by at least the depth of the paving bricks, probably more. The paving bricks, then, will have taken the surface level higher than when the house was built, probably close to or bridging the DPC, which is probably why a chemical injection was tried.

    1) please look for any sign of the original DPC. Sometimes it is visible at an original doorway. When the house was built it will have had one, and it will have prevented damp walls inside the house. Putting render over a DPC allows damp to bypass it.

    2) please photograph the gulley, showing where the gully grill is, in relation to current surface level, and the water level, and any signs on sinking, cracking or repairs around it.
     
  9. profile50e

    profile50e

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    Hi John,

    I had a damp proof firm come and take a look today and from what they can tell, there is a portion of wall where the damp course treatment has either failed or wasn't done at all. The bay area all round the other side is bone dry and it is just this section of wall where there is rising damp. They also though the original damp course is above the render in any case, but either way it looks like I need to go ahead and get the render off the wall on this narrow section and get it treated.

    The gully by the the way - you are right, it is more than one paving stone down and the water level is probably 30-40cm below the grille.
     
  10. JohnD

    JohnD

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    the gulley is probably cracked or broken in the ground, and leaking. This is common. The leak washes away the ground and causes the gulley to sink. There are usually signs of ineffective patching and filling of the cracks ands subsidence in the nearby paving. A cracked gulley has to be dug out and renewed.

    Chemical injections do not repair sources of damp, but people who sell it are happy to sell you some more.

    There is little doubt that your house was originally built with a DPC (most often slate) that worked. Slate lasts for at least 500 million years. Find out what has defeated it (probably bridging, including render, raised ground levels, or rubble in walls) and correct the fault.

    It is noteworthy that your damp patch is close to a drain that is probably leaking.
     
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