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Rendered wall wet at the bottom after rain

Discussion in 'Building' started by Screamingaddabs, 23 Sep 2019.

  1. Screamingaddabs

    Screamingaddabs

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    Hi there. We have recently had an extension built onto the house that has been finished with pebble dash render. After rain, one particular section of the wall often has large dark damp patches towards the bottom (wider at the bottom than at the top - see the attached photo). Internally there is no sign of any moisture but it is a concern nonetheless. Our builder is not exactly good at communication and simply says that he "gets the same thing at his house" without offering a decent explanation of what is happening and why. Is this something to be concerned about (feels like it is!)

    Any advice would be appreciated! Thanks!
     

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  3. JohnD

    JohnD

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    stand back and take a wider pic of the whole wall please

    including the leaking gutter above.

    Also please kneel down and take a pic at ground level and a foot above.

    Where is the DPC?

    Where is the drip?

    Was the pebbledash done by an experienced British renderer?
    (clue: No)

    If you scrape away that gravel, how deep is it, and what's underneath, at the centre of the wet patch?

    What's inside, on that wall, at the centre of the wet patch?

    What does that drain do?
     
  4. Screamingaddabs

    Screamingaddabs

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    Hi John, thanks for the reply. I will get back properly with more pictures tomorrow morning (it's due to rain tonight).

    Below the gravel is concrete. Our builder put it in as a side path. We were forced to pave over it away from the house as his rough concrete was crap. The gravel fills the gap between the paving and the house. It is about an inch or so deep.

    There is no gutter above, it's the end of the house.

    I'm not sure what level the damp proof coursing is at. We were told by our builder that it is at the level of the bottom of the render, which seems too low to me.

    I don't understand the "where is the drip" question, sorry.

    The guys that did the work we ended up kicking off the job for doing crap internal plastering and using racist language.

    The drain you can see is not a proper drain. For the purposes of this you may as well assume there is no drain there.

    On the inside of the house is the kitchen. Backing onto the wall are kitchen units.

    Apologies for anything I have got wrong, I'm not in the trade at all.

    Thanks again for the help so far. What do you expect are the most likely causes and is this something that needs to be fixed immediately (I'm guessing yes)
     
  5. JohnD

    JohnD

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    the render should not go down to ground level. It should stop about ten inches above, and there should be a stainless bell-shaped strip "drip" so that any water running down the wall drips off. The DPC in the brickwork should be at about the same height. Yours does not seem to have been correctly applied. If that's the only problem (but I think not) it could be cut back and re-finished.

    If the dpc is truly at the level of the bottom of the render, then the ground level is too high. This often happens when people lay new paving or concrete without digging up the old. It often leads to the DPC being bridged and damp in the wall.

    Render on a wall encourages water to rise due to capillary action. Good bare brickwork, with no plaster or render, is surprisingly resistant to this.

    The shape of your wet patch suggests a source of water at about the point the patch is highest. It has the look of water falling from a gutter or downpipe. It will be interesting to see the shape of the roof for any clues. If it's not that it might possibly be a broken or faulty drain, but that's not visible. Do you remember any drains along that side of the house? If you look at the downpipes at the back of the house you might be able to work out how they get past the house to the sewer under the road. If there used to be downpipes or drains before the extension was built that could be related. Any drawings or photos you have, and the position of any manholes, will help. If the neighbours house is to the same design, their drains and downpipes were probably built just the same.

    Was the extension built of bricks, or lightweight blocks? Do you recall how thick they were, and if there is a cavity in the wall? It is possible, but not common, for water to get into a cavity at the top and run down inside the wall.

    Why is there a "not a drain?"
     
  6. Screamingaddabs

    Screamingaddabs

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    Hi John, thanks again for the further response. Please see the attached addtional photos. It did rain last night (as you can see!). There is a similar damp patch on the garage wall this morning (nearer the camera) that was not there in the previous picture. I had thought, based on your prior comments, that perhaps the rain water is coming off the edge of the roof and the wind (which blows predominantly towards the wall in question) is then blowing it into the wall as it drips down. The garage roof is only single story and so there is less distance for the water to fall and so less time for the water to be blown into the wall, hence why it seems to not get damp. This morning however, the garage part also looks damp...

    The "not a drain" is actually a circular inspection point that is lidded so doesn't drain anywhere. The drain like cover just sits over the top.

    It looks like the drip is poorly done.

    The walls under the render are cement board rather than brick (see other picture).

    The drains run underneath the garage and kitchen.

    The concrete was laid by the builder that did the extension. The additional paving was done by somebody else on top of the concrete as the concrete was left as a very rough finish. The second contractor put the gravel area adjacent to the house to avoid raising the level any further.

    Let me know if any more info would be useful, apologies if anything is not clear.

    I guess the ultimate question will be "what can we do about it?" (apart from "not start from here"!)
     

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  7. Screamingaddabs

    Screamingaddabs

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    Sorry, just to add that apparently the DPC is two inches above the bottom of the render. Miscommunication between myself and my wife (who spoke tot he builder about it).
     
  8. JohnD

    JohnD

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    that's the easy bit, then.

    the render will tend to bridge the damp course and allow water to rise into the wall above. But that can be fixed by cutting it back and chipping off the render on and below the DPC.

    A builder/bricklayer who does repointing will probably have a small diamond disk cutter suitable for slitting the render so it can be knocked off without cracking the rest of it. There may be other ways.

    If you look down your inspection cover (i think it might be a rodding eye), what do you see? It suggests that a drain runs in the ground beside the house, as expected, and this might be the source of the water, for example if it is blocked, and there is a crack causing the water to rise up at the wet point. The render is in contact, or very close to, the ground/concrete. It's possible that rain is flooding that gap and wetting the wall. Have a look with a torch next time it rains heavily.

    I'm thinking it may be necessary to excavate (at least) a channel beside the wall; both to see if there is a problem with water coming out of a drain, and, if not, to isolate the bottom of the render from the wet ground. It will be at least six inches wide and deep, preferably a foot. These channels are filled with cobbles or large clean stones, which do not cause capillarity (rising damp) because the gaps between stones are too big, and are usually sloped to let water run away. It is called a French Drain. When you dig a hole next to a broken drain, the hole fills with water if the drain is broken, this is quite distinctive (and surprising if your neighbour has a bath while you're working).

    Looking at your pics, I think I was wrong to suspect the roof, it doesn't look like water will be coming off there.
     
    Last edited: 24 Sep 2019
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