Rendering advice

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dlacheson

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I am new to this trade as I'm still learning at college. I recently did a repair job on a friends outside render. I used a mix of 4 sand (rendering), 1 cement and 1 lime. I cleaned up the backround and dampened it down before I applied the material using two applications. When I went back to see the job three days later, I noticed that hairline cracks had appeared in the render. Can anyone tell me how this could have been caused or how it can be prevented. Thanks.
 
Your background might of been to dry even though you dampened it , or maybe it dried to quickly if the sun was shining on it. did you use any waterproofer or plasticiser in your mix lad.
 
I don't think there was much sun that day, and it was fairly cold. I didn't use any waterproofer or plasticiser, should I have done?
Someone told me that I might have had the mix too wet (although I don't think so) and that I rubbed it up too soon.
 
Platiciser is elasticted helps prevents cracking , i usually put waterproof on scratch then platiciser on top coat, did you make your top coat weaker or stronger than your scratch coat lad ?
 
dlacheson said:
I am new to this trade as I'm still learning at college. I recently did a repair job on a friends outside render. I used a mix of 4 sand (rendering), 1 cement and 1 lime. I cleaned up the backround and dampened it down before I applied the material using two applications. When I went back to see the job three days later, I noticed that hairline cracks had appeared in the render. Can anyone tell me how this could have been caused or how it can be prevented. Thanks.
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i norm doing a repair first hit 3 to 1 or less depending on size dont put a pissy first coat on a repair
 
dlacheson said:
Thanks to everyone who replied. I'm going to be doing it again this weekend, so wish me luck.
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Im sure you'll do a cracking job mate ............ sorry couldnt help myself mate lol

Rich
 
steve1976 said:
Platiciser is elasticted helps prevents cracking , i usually put waterproof on scratch then platiciser on top coat, did you make your top coat weaker or stronger than your scratch coat lad ?
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Where the hell did you read that in the daily sport, Feb and its equivalents only improve the mucs workability and in no way prevent cracking.............If you only put wat/proof in base coat what happends to the top coat in the winter when water penertrates it and freezes ?????
 
what do you do somerset w/proofer all the way through or none at all?
 
When waterproofing the top coat its sets the motar hard and dosent allow to move that causes cracks, where by using lime or plasticiser lets your motar stretch a bit .
 
In the summer I use waterproofer in both coats but in winter I use plasticiser in the scratch and waterproofer in the top coat.

Rich
 
I see what rich is sayin.. waterproofer in the scratch in winter will leave you layin the float coat on following morning and floating it up about 9 oclock that night..
if your lucky..
 
theres always rapid hardener or quickcem but to be honest i only used it once over a plastic membrane and it pretty much went off in the barrow!
Best to ask church on that one..
 
sorry slightly off topic doeas anyone know how many metres a tonne of sand will do one and two coat ?
 
i reckon to do 40ish meters from a ton at between 15mm and 20mm thick includes 5 opc and 3 lime
 
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