hair line cracks in render

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28 Mar 2009
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Sussex
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United Kingdom
Can anyone tell me why i sometimes get hairline cracks in my render? I wet the blocks down with a hose then leave 10 mins, on with the scratch coat. 4 plastering sand, 1 cement with waterproofer. Leave a few days then on with the top coat: 5 plastering sand, 1 cement ,1 lime. Apply top coat, rule off, float and sponge. Come back next morning, CRACKS!! I thought it was to do with direct sunlight drying too fast but a recent wall was in shadow all day and still cracked. I have tried adding a shovel of building sand to put some fat in the mix, putting waterproofer in the top coat and other combinations but still end up with a crazing to the finish.I have wondered if it could be the weight of the top coat pulling down but i'm only going on between 8-10 mm, wouldn't want to go on any thinner. Any help please?
 
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It could be drying out too quickly, if there is a bit of wind on it or sun . What I have done in the past is if its windy or sunny I have put sheets over the scaffold to shade it and also returned a few times later on to give it a gently hose down or a good light spraying with water to stop the outer coat drying out too quickly, In warmer weather you have to keep your eye on it so it doesn't dry too quick. When you put your top coat on are you wetting up the scratch before top coating?,,,
 

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