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Patching garage walls with render advice required

Discussion in 'Plastering and Rendering' started by angularbanjo, 3 Mar 2010.

  1. angularbanjo

    angularbanjo

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    Hi there

    We have a single garage which seems to be a concrete block construction (the blocks even on the inside are a bit 'crumbly' so I'm guessing low density) with rendering/harling on the ouside, down to about 18 inches of brick at the bottom.

    The rendering has cracked and fallen off about 2 feet either side of a corner leaving a biggish patch exposed and in need of repair. The rendering seems to have taken away some of the surface of the concrete blocks as it became detached leaving very rough and uneven blocks.

    I quite fancy tackling this job myself once it warms up a bit outside and wondered if anyone could offer any advice re how best to avoid all the work being for nothing and the whole lot just falling off a few months later!?

    I'm guessing I might need to apply an initial layer of something to the rough exposed blocks before applying the main layer of render?

    I'm also not sure how to tackle the corner and get a neat 90 degree finish (although to be honest I'm not that bothered about its appearance, main priority is weather tight)

    The garage roof is corrugated metal (?aluminium) nailed onto wooden roof joists. The roof is not watertight at the back where the render came off so I'm guessing that water has maybe got in behind the render then frozen/expanded pushing the render off. I'm guessing that a priority will be to stop the water getting in, so some detective work is also called for.

    Anyway, all advice about how best to tackle the job or even pointed in the direction of existing online resources would be very very helpful.

    Thanks in advance

    Steve
     
  2. Micilin

    Micilin

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    You are of course right to find out the cause of the damage first, and the bad weather may help you do this (silver lining?)

    Chief suspect is as you say ingress of water.

    Also possible is damp caused by material being heaped up against the wall on the other side (not likely in this case) or rising damp or some other leak or water being thrown against the render and getting in a crack etc.(not likely but possible)

    If you can find some way of throwing the water off the wall - such as introducing a band of flashing on the top of the wall to protect it, or making up a fascia board that will do the job, that would seem to be the best remedy of treating the cause rather than the symptom.

    As regards the repair itself you will be able to do it yourself.

    To repair, remove all loose/flaking render. Check all over the garage for bits that sound live (hollow) by tapping it an listening for a different noise.

    Clean with a wet brush to remove all dust.
    If it is a rough surface, you will be okay to render on to it, but more likely you will have to give it a coat of something like SBR:Sand :Cement (1:1:!1 ) with a brush, rub it well in.

    Let this dry and next day, brush on SBR Cement(1:1).

    While this is tacky, apply a coat of sand and cement (4:1) and scratch it for a key. (you can use SBR as a waterproofer in this mix seeing as you bought it already!) This coat has to be set back from the surface of adjacent finished render by about 12 mm.

    Then after a couple of days you can render it up with a final coat of render (say 5:1)

    To form the angle, use a timber batten to do one side, nailed on in line with the finished surface, so one side ,then take off the timber and return it to form the other side.
     
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  4. angularbanjo

    angularbanjo

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    That's really helpful, thanks for getting back to me.
     
  5. Micilin

    Micilin

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    No worries, is the finish a rubbed up render or does it look like stones thrown in it?
     
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  7. angularbanjo

    angularbanjo

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    Yes, it's finished with the wee stones, what I've always understood as harling?

    I don't think I'lll get an exact match but I'll get the closest I can then basically chuck them at the wet render with a tarp underneath?
     
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