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Water ingress through tanking slurry

Discussion in 'Building' started by diry, 8 Jan 2017.

  1. diry

    diry

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    About a month before Christmas I put 2 coats of KA tanking slurry on the interior of a single skin walled outbuilding (coal shed attached to house) - halfway up walls and over whole floor - as these walls have always been damp as the DPC is bridged but a concrete shed base in a neighbours garden which has been there for 8 years before we moved in.

    (Obviously the best course of action would be to resolve the bridging by digging up the shed base and providing adequate drainage and a damp proof membrane on the outside of the building but this could not be done for 'diplomacy reasons')

    All has been well, although today has been a miserable day and it's been raining most of the day and I noticed water on the inside of the walls again - does this mean my tanking has failed?

    After this I had planned to batton out the walls at 400mm spacing and put 25mm celetex in each gap with foil tape sealing off between the battens and 12.5mm moisture resistant plasterboard on top of this - I do not intend to drill holes though the tanking slurry to fix the battons on the bottom half of the wall and had intended to fix with a grab adhesive.

    The floor I have created 18mm ply panels which I also intend to put celetex under when it is back in stock at wickes

    The only other thing I am thinking is that perhaps the tanking slurry hasn't fully cured yet?

    Cheers
     

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  3. DaveHerns

    DaveHerns

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    It's been mild today in Surrey so are you sure it's not condensation?
     
  4. diry

    diry

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    Cor blimey, it's been real miserable drizzle and rain most of the day at our house in Guildford.

    It is worse today than it has been previously.

    The particular areas that are wet are the areas where the bricks were saturated before the tanking treatment, so I guess that area of the wall could be 'colder' so it's possible it could be condensation I suppose - I'm not sure how I can be sure of that though.

    Most of the wall, as far as I can see, has dried and is a light grey. The areas where the bricks were daturated pre-treatment have always remained 'damp looking' but today very wet with droplets running down the wall.

    I hope it is just condensation :)

    Cheers
     
  5. vinn

    vinn

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    KA tanking takes about 3 days to cure or dry.
    AFAIK best results come from applying to a clean dry surface.
    Where ground water pressure is penetrating the wall or floor then special conditions of installation must be met.
    Personally, I wouldn't use it.
     
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  7. r896neo

    r896neo

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    Best results come from applying to a damp substrate in my experience. If it dries too quickly it can be less effective as it uses the dampness in the masonary to permeate itself into the wall.

    I have only used it in ponds and they are all watertight years later.

    What are you trying to do to this room? Plasterboard and single skin structures are not a good combination in my book. If trying to convert this to a semi habitable space you need to go down the proper tanking route with a cavity membrane because of the potential hydrostatic pressure on the far side of the wall.

    KA and other tanking slurries are only as strong as what they are applied to i.e Brand new solid structures and i would be hesitant to recommend them for any older outbuildings which no doubt have the odd crack here and there and perhaps subtle movement.
     
  8. diry

    diry

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    Fair enough. The instructions on the packaging indeed suggested to apply to a damp wall, suggesting the damper, the better for the same reason you mentioned; they said to wet for 24 hours and then once more just before application.

    After closer inspection I wonder if it is not just condensation as suggested by Dave as you can see tiny little water droplets all over particular areas (The same areas that used to be just damp bricks).

    That being said, the plan is to turn this old coal shed into a utility room with a sink, the washing machine, an undercounter fridge and an undercounter freezer - this room also currently houses the boiler and there was a high cistern toilet in a small closet which we are changing to a back to wall toilet

    Just had a look into cavity membranes as you have mentioned, perhaps this is the route I should have gone with to begin with!

    I have applied the tanking slurry 1.2m high for the perimeter of the outbuilding, so the top half is still permeable brick - so if I retrospectively apply a cavity membrane any moisture should be able to escape higher up as it evapourates (I see some membranes are dimpled to allow for movement of water vapour).

    That being said, since part of the wall is below ground level if I hadn't tanked it'd always be wet and no water would permeate out through the bottom 5-6 bricks anyway and will always seep in when it rains so perhaps the tanking may somewhat aid in preventing lots of water coming in and then with the addition of a cavity membrane prior to battoning and boarding out the room I should hopefully avoid any damp issues in the future.

    Whatever I do, I just want to do it right.

    Cheers
     
    Last edited: 9 Jan 2017
  9. vinn

    vinn

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    Taking up suction would depend on the background and other factors.
    A primer could always be concocted using SBR and whatever.
    But, no matter the Mfr's claims, I see going on to what I would consider an excessively wet background a recipe for failure.

    To my mind there are two considerations: one is the water pressure coming through the background, and two the strong possibility of condensation on the impervious surface of KA.

    Membranes are something else - one membrane consideration would be what happens if the KA is blown behind the membrane.
    I know what happens - slime and mould accumulate, and water can appear at the foot of the wall unless its channeled and pumped.

    I dont know much about this business but I do know that its relatively new say 50 yrs, and many chickens might yet come home to roost. Same for the whole remedial Industry really.
     
  10. diry

    diry

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    It's all swings and roundabouts isn't it!

    Cheers for the help :)
     
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