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External wall cracking, peeling & flaking.

  • 06-05-2008 10:54pm
    #1
    10-10-20
    Registered Users, Registered Users 2 Posts: 7,744 ✭✭✭


    Hi guys,

    I wonder if anybody could hazard a guess as to the cause of this issue on two corners of my external walls.

    http://pix.ie/10-10-20/526872

    http://pix.ie/10-10-20/526871

    The wooden baluster in the second photo is at the level of the upstairs balcony.

    It's happening both at the bottom of two walls where they meet the ground and also further up the walls at 10ft approx.

    On examining the damage, the plaster/screed underneath was found to be sandy and soft and readily falls away from the sub-layer. No external damage has occurred to the wall.

    Both the adjoining walls, which make up the corners, face South-West and South East, with the corner facing south - per-say. The site is somewhat exposed, being the last house in the row and taking a fair beating from the westerly wind & rain.

    My initial worry was rising damp, but the fact that the issue occurs on two corners and at >10ft high makes me believe that this is not so.
    I also thought about a poor mix of skim/plaster (being sandy), but I don't see how this could be true, again with two corners affected and nowhere else on the walls.
    I do have to point out that there is no concrete path around the exterior of the house, it's simply shale and the drainage is very good (no standing water).

    Can anybody give me pointers?


Comments

  • #2
    sinnerboy
    Closed Accounts Posts: 5,433 ✭✭✭sinnerboy


    most likley the strength ( cement content ) of your render layers is wrong

    let me explain

    traditional smooth render should be applied in 3 stages , with each layer getting weaker as you move out from the wall

    1 . scud coat . strongest coat - most cement rich . it is "splashed on" . rougher the better - and genorously applied all over to create a key - a grip - hold to the wall . it must be allowed to harden for at least a week .
    mix 2 parts sand 1 part cement

    2. scratch coat .
    10-15mm . trowel on allow initial set , but when still soft scratch all over with an 6 inch nail-brush . mix 4 part sand 1 part cement . leave for min 1 week

    3. final coat . 8-10mm . trowel on . mix 4 part sand 1 part lime 1 part cement or even 6 1 1

    the mix strengths get weaker as you move away from the wall


    In the photo your top coat looks cement rich i.e. very strong . it acts like a stretched elastic band trying to shrink back . You say the undercoat is sandy . Sounds like the top coat it literaly tearing the base coat away . The fact this is happening at a place where there is expanded metal increases the key for the render only tends to support this proposition .


  • #3
    10-10-20
    Registered Users, Registered Users 2 Posts: 7,744 ✭✭✭10-10-20


    Hi sinnerboy.

    Thanks for the reply. I have a feeling you're correct. I'll have to hoke out the layers and see what I find. The house was built in 2003, before I bought it. Let's just say I have a few issues... http://www.boards.ie/vbulletin/showthread.php?t=2055274085

    :)
    More to follow!


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