Lime render cracking - please help

J

J18usr

New Member
Hi guys I need some tips pls. I've lime rendered a few chimney recesses recently and they seem to be cracking! I prep the brick work as normal cleaning it off and then applying 2 coats of PVA. Knock up 4 sand 1 lime and 1 cement. Once scratch coat and top coat applied it seems to hang around lovely but 3 customers have reported cracking within 24hrs. Any tips would be gratefully received.
Thanks
 
Over here (US) in our area we found that a lot of cracking like you have going on was caused by sand that was too rounded off. Our materials supplier found a source that supplied sharper sand and that has helped a lot. A lot of grumbling went on about the sharper sand because it seems to be a little harder to work with, but nobody remembers how hard it was to work they all remember that cracked up wall you left behind though. Maybe try a 4.5 sand, 1 lime & 1 cement could be your mix was too rich, did you keep it wet down after your rendering set off? I've been using a stucco mix with everything in the sack all you have to do is add water it's also got fine shredded fiberglass fibers in the mix. You never have to worry about having more than one open sack left over, and you just don't see any cracking going on. https://www.basalite.com/products/packaged-concrete/stucco-products/sakrete-scratch-and-brown-stucco , maybe the UK has something similar.
 
Welcome to the forum,What lime did you use nhl or hydrated?it should be hydrated with cement just as a plasticiser?adding cement makes it sand and cement render not lime mortar,how long did you leave the scratch coat before you topped it?also do you want to know tips on how you should have sand and cement rendered it or the equivalent in lime?
 
lime render would be nhl and sand no cement .what you used was a standard mortor mix .i wouldn't have used pva first coat would be a scud coat as we call it or slurry coat then a scratch at 4'1'1 or even 5'1'1 then a top coat of 5'1'1 or 6'1'1 depending on the strength of your scratch coat ,and give each coat time to cure
 
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