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Do moist blocks shrink enough to explain my hairline cracks?

Discussion in 'Building' started by Rob broom, 21 Apr 2021.

  1. Rob broom

    Rob broom

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    Hello again!

    Quick question about laying moist dense blocks?

    I laid 3 courses of 10.4 dense (Dennis May) blocks about three weeks ago. I layed one course per day over three days. The weather was cool, damp and the odd bit of rain and snow was around.

    The blocks were stored on a pallet in my garden, exposed to the elements.
    They have been there for months.

    I currently have a crack phobia, so I’ve been inspecting my walls daily with a magnifying glass.

    There are very tiny (less than hairline) cracks in these recent courses, in some of the mortar joints. I cannot see Cracks in the courses below, that have been there for a couple of months. The cracks are mainly vertical and a couple short horizontal. They seam to be in random places, rather than in one area.

    mortar mix was about 4 and a half sand to 1 cement, with admix.

    The courses in question are about 19 blocks long, just under 8m


    I’ve just been and looked at the left over blocks on the pallet in the garden, picked one up and it is still moist/damp on the back. So that suggests that the blocks are damp and would have been so when I laid them.

    Does the fact that the area in question is south facing, plus that we have been blessed with lovely sunshine for the past two or three weeks, suggest that the blocks have dried out and shrunk enough to cause theses cracks?

    do concrete blocks swell enough, that when you put 19 in a row and they are allowed to completely dry, mean they will shrink enough to cause the odd crack?

    I just wondered if anyone can put my mind at rest once again?



    Many thanks.
     
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  3. jeds

    jeds

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    8m is approximately the maximum without introducing an expansion joint - maybe a tad more. So you're not on the limit but you are close to it, and that's if everything else is spot on. Get the mortar too strong and you will get cracking. My advice; lose the magnifying glass.
     
  4. Rob broom

    Rob broom

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    Cheers Jed’s.

    I’m coming to terms with the chance of cracks.

    they’re only hairline at the mo, so fingers crossed they won’t get bigger!

    I’ll put the magnifying glass away!

    Im not going to be rendering the wall for a long time, so I’ll have a chance to monitor it!

    thanks again!
     
  5. ^woody^

    ^woody^

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    Now I'm having deja-deja-vu :cautious:
     
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  6. tony1851

    tony1851

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    Crackaphobia - no known treatment at present, though A.Z. are thought to be working on a vaccine.
    In the meantime, sufferers are instructed not to go within 2m of unplastered walls.
     
  7. ^woody^

    ^woody^

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    I thought of asking him "How's the craic?"
     
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