Damp patches on plaster 6 months after damp proof course was injected

Discussion in 'Builders' Talk' started by JJJP, Oct 22, 2018.

  1. JJJP

    JJJP New Member


    About 6 months ago, I got a damp proof course put in. The walls were tanked (over 1 m high) with tanking slurry plus base and top coats of sand and cement with water proofer (sika 1) were applied. I've now painted on the mist coat (watered down Dulux).

    The dpc seems to have worked, as the exterior walls are almost completely dry (though there are a few blotchy patches of damp – roughly one small patch per wall – where the mist coat is darker than in the dry areas).

    The main problem is that on the two internal walls (either side of the stairs), there are multiple patches of damp all over the bottom 1 m of the wall (where the wall was wet due to rising damp). The damp patches don't start at the bottom of the wall and go up. Instead, the damp is in blotchy patches on one of the walls, and in more of a band on the other one, which you can see in the photo (though it's not a continuous band, and there are still blotchy patches, e.g., one a few inches from the ground on the far right of the wall, not in the photo).

    The downstairs rooms all have floorboards (no cement next to the two affected walls). The other side of each of the two affected walls (the walls of the cupboard under the stairs) seems fine – there was some salt coming through the mist coat, but no damp patches.

    The damp proofer/plasterer who did the job came back and isn't sure what's going on. He suggested painting the next coat and the top coat, as it might be that the affected patches are just cold patches on the wall. However, some of the mist coat had already began to peel, and when I painted over it, that coat too began to peel in places due to the damp. (Btw, the patches are damp to the touch, but his damp metre apparently wasn't picking up any readings of damp, so I'm not sure how to interpret that – he said the metre gave readings for the top layer of plaster.)

    I don't think the dpc has necessarily failed, but I was wondering if anyone knows why the damp patches have occurred given that the plaster is supposedly protected by the tanking/water proofer. And why does the damp occur only in certain patches?

    Please let me know if any more details would be helpful to work out what the problem is. Thanks for your help.

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  2. ajohn

    ajohn Screwfix Select

    Maybe you have painted too soon and should have used bare plaster paint to allow the work underneath to fully dry out.

    DIY womble likes this.
  3. JJJP

    JJJP New Member

    Hi, I waited about 6 months before putting on the mist coat (other things in the house were being done in the meantime). Before the walls were mist coated, the differences in the plaster between the damp patch areas and the rest weren't that clear (though on the worst wall, the plaster was a little orangey in places rather than pinkish), but very clear darker-coloured patches can be seen now that the mist coat has gone on, and these patches are damp to the touch.
  4. ajohn

    ajohn Screwfix Select

    It's not an area I know much about other than a dp lot telling us my wife's house was damp when we sold it and having to cough up. Blue brick damp course which isn't as good as modern methods due to the mortar. There clearly was no damp problem - the bloke even reckoned some stud partitioning was damp. The house we are in now has the same. The surveyor mentioned that nothing should go over the blue bricks - render does slightly but having been here 30 odd years I am 100% sure we do not have a damp problem - ;) I'm not keen on decorating and some paper has been on the walls for a lot longer and never repainted. The person we bought it off said they had a problem in one downstairs room - water pipes in a trench and joints leaking - :) Never know if it's a good idea to believe people who are selling their own house but some dp work was done internally on one section of wall that is in the right place for that sort of problem.

    Only thing I can suggest is that you look around for water leaks. They can be anywhere. Pipes, toilet, bath, guttering, down pipes, roof and probably other places as well such as the sewer end. Also check outside for anything that should be lower. We did have a patch in a loft room down to a leak in the roof before the roof was fixed and later replaced. The water was running slowly down a timber in the roof structure from some flashing. The fact that the timber was damp helped locate it.

    Having checked that sort of thing I assume you have a guarantee - the fact that the person that did it has no idea what is going on is irrelevant. They need to fix it. No guarantee isn't a good idea on work like this.

  5. JJJP

    JJJP New Member

    Hi, thanks for your reply. There is a 30-year guarantee on the damp work, but I haven’t heard back about it even after calling… I will look into whether there’s a leak somewhere (though there aren’t any pipes nearby, so it’s not immediately obvious where it would be coming from, plus the damp proofer tanked the walls etc.)
  6. ajohn

    ajohn Screwfix Select

    I think you will find that even a gutter leaking can cause damp patches to appear downstairs so the water could be coming from almost anywhere. If the leak always misses the wall all should be ok - if it doesn't that's when problems happen. On that basis it could even be caused by leaks in the roof. As damp proof courses can fail water can also work it's way up.

    I bought a cheap damp meter to check how quickly some leveller I had used was drying before tiling. Cheap as it's intended for timber. We have exposed the wall in places so I also ran it over that. Bit concerned even though the readings wouldn't match one intended for the job. I found a web site that went into some detail about readings. What should happen is the reading should drop further and further up the wall. The page also mentioned checking upstairs and noticing areas with higher readings in places. I honestly don't know but that sort of approach might help. In my case I was happy as the readings behaved just as they should. ;) Interestingly selecting different timbers didn't make much difference.

    If I had problems with a contractor like this I think I would want a second opinion. In your case a buildings surveyor might be ideal. Not looking for work, just doing their job. if you explain that you have problems your local buildings inspector might take a look and have the correct kit and be able to judge the standard of the work. Either might cost.

    Yours is an interesting post. If I ever find that this sort of work needs doing I'll make dam sure that it is only the damp course. If it is in your case then something is wrong with the work. Threatening to have it done again followed by a small claims action can help in that case but then you really do need a second opinion.

  7. JJJP

    JJJP New Member

    Hi, I think getting a second opinion from a buildings surveyor sounds like a good idea - thanks

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