Badly blown render - help

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Theo

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Hi, can anyone help me. Ive had my house rendered twice on new concrete block and both times the render has cracked, blown and fallen off!

The process he has been using is the first time was - Pva walls, a scratch coat 4.1 with 900ml of waterproofer/retarder (3 large mugs), the next day top coated using 4.1.1 (washed sand,white cement,hydrated lime) 900ml of waterproofer. It looks good for about 3 days, on the 4th day hairline cracks appear, day 5 large cracks appear and top coat blows. Top coat sticking to scratch coat, and scratch coat sticking to wall. It seems the scratch coat is seperating and is really dusty.

The second time house was rendered the same thing happened but using a 3.1 scratch coat.

Can anyone help, this is costing me a fortune!

Thanks
 
Would never advise using pva on externals also scratch should be left to dry minimum of a week idealy
 
Yep, leave the scratch coat for a week and keep the moisture in it, by hosing it down for 2 or 3 days after it's been applied:RpS_thumbup:
 
bubbles65 said:
Yep, leave the scratch coat for a week and keep the moisture in it, by hosing it down for 2 or 3 days after it's been applied:RpS_thumbup:
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You have been living in the uk for the last 2 months ? we spend more time keeping the rain out !!:huh:
 
there is to much waterproofe in the mix. it has weakend the mix . i would have used sharpe sand to scratchcoat. then mixed a plastering sand into the top coat. not washed sand.
 
Try reading the cement bag that white cement is some funny old s**t it needs to be gauged carefully try using a different cement in the mix and go easy on the waterproofer,and also pva on conker block is normally a no no I've never ever pva on an external before.hope some of this helps :)
 
Why is it costing you a fortune? Surely the bloke that has fecked it up is redoing it out of his own pocket, after all he has done every aspect of the job incorrectly.
 
as said, leave the scratch to cure proper, least 2-3 days.... less waterproofer too. SBR the wall first if you like, that scratch coat wont go anywhere then lol

your top coat shaould always be weaker than the one below it....so 4-1 scratch.....5-1 top etc
i use FREEFLOW by cemento, exelent stuff and you only need 2 cap fulls for you top coat and its sealed a goodn!
 
long as you water down the pva enough it will only act as a stabilizer on the background, ensuring the first coat to get a good grip on the bricks etc. neat however has the opposite effect, like a skin.
 
If I,am understanding right you are using nearly a litre, 900ml of water-proofer to a 4.1? ffs, apologies if wrong.
Also why are you using white cement?
Who is this person you have employed? do you have any pictures? of the person and work?

Seriously if anyone can mess a render job up on NEW concrete blocks they need hanging, its a crime mate.

hope you get it sorted

Rock on !
 
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