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?