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Rendering cracking

Discussion in 'Plastering and Rendering' started by weird_dave, 31 May 2009.

  1. weird_dave

    weird_dave

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    I've just attempted to render some areas after burying pipes into the wall. It's cracking after about 20 minutes, it hasn't set fully yet.
    I'm new at this and would appreciate any insight.
    The mix I used was 3:1.
     
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  3. roughcaster

    roughcaster

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    Possible causes.
    Too much suction?,, did you wet/soak the block/brickwork down first? Did you scratchcoat the areas first, or did you just fill it out in one go? Was there waterproofer/plasticiser in the mix? Was the mortar properly mixed,, aerated/light,,, or was it heavy to spread/use, causing it to slump/split? Was the hot sun beating down on the render causing it to dry out too quick? Too strong a mix? These are some of the reasons that can contribute to render cracking.

    Roughcaster.
     
  4. weird_dave

    weird_dave

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    I did spray water onto the brickwork before rendering.
    I didn't scratchcoat as I've only just googled it.
    I didn't use any plasticiser.
    It looked well mixed enough, I spent long enough mixing it!
    Heavy to use? Not sure I understand that, how would you make it less heavy?
    The sun can't reach the render, but it was a warm day.
    It seems to be attached to the wall alright, I'll be tiling over it at some point so hopefully the eyesore that is my handywork won't be a problem.
     
  5. roughcaster

    roughcaster

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    Sorry about the jargon! If mortar is mixed without a plasticiser added, it will be what is termed as heavy,, lifeless, especially if it has to be spread onto a wall. Plasticiser puts air into mortar making it very light and easy to use,, fluffy, buttery,, easy to spread,,, lime helps too. Waterproofer in the mix stops any suction in the wall. A combined waterproofer/plasticiser called Evo-Plast is one that I use, but there are other brands. It's always worth scratchcoating first too.

    Roughcaster.
     
  6. weird_dave

    weird_dave

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    Ah, interesting stuff! I'll bookmark this for when I do the kitchen...
    Well, it's stayed on the wall overnight, I guess it'll be alright.

    Thanks Roughcaster :)
     
  7. roughcaster

    roughcaster

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    Good luck to ya W'/Dave,,, any more, ask anytime. ;)

    Roughcaster.
     
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