Crazed s&c render

Always a opinion :LOL:
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Lox said:
Crazed render is a suction issue not movement ! Or has the blocks exploded and cracked everywhere
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Yea ok, I can only tell u what I’ve found in 37 years of plastering, I’ve had it happen to me , even on my own extension, and trust me , I sbr slurried the blockwork and while still wet applied scratch coat with waterproofer in it, I even threw fibres in the scratch ( something I’ve never done before) , cured the render for days , and I stil got cracks , all pretty sound but cracks nevertheless, definitely thermal movement
 
thee_catfish said:
So if it doesn't fill cracks is it to bond it to the scratch to stop further cracking and possibly coming loose. If I'm right do I win a choccy egg
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I'm pleased your back ,
Its to give it thermal stress and hopefully show any cracking which nay occur after you painted and the weather chops and changes in extreme
I expect a few more cracks to appear but better now before the paint
You said it was sound and I'm sure it'll be OK
Stress it , fill it , paint it , never had to try this before , lol but its no bother to hose a wall on a hot day in comparison to attempting to fill or cover straight off , what do you think
 
Havagojo said:
I'm pleased your back ,
Its to give it thermal stress and hopefully show any cracking which nay occur after you painted and the weather chops and changes in extreme
I expect a few more cracks to appear but better now before the paint
You said it was sound and I'm sure it'll be OK
Stress it , fill it , paint it , never had to try this before , lol but its no bother to hose a wall on a hot day in comparison to attempting to fill or cover straight off , what do you think
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Makes perfect sense. I'm back there Wednesday to do a few last bits so will try that before starting any repair work. Hopefully it's still hot by then. Appreciate the advice, cheers
 
I was taught at College that 1 lime should be to at least 6 sand. Less than 6 sand and you risk cracking due to expansion.

Maybe 1 soft sand to 5 sharp if it is gritty.

Have you thought about applying a thin coat like Weber lac? 4-6 mm with mesh and if you cant get it really smooth when wet scrape any lines out when set and smooth out with a carborundum stone. Might end up making the rest look naff though.
 
Rigsby said:
I was taught at College that 1 lime should be to at least 6 sand. Less than 6 sand and you risk cracking due to expansion.

Maybe 1 soft sand to 5 sharp if it is gritty.

Have you thought about applying a thin coat like Weber lac? 4-6 mm with mesh and if you cant get it really smooth when wet scrape any lines out when set and smooth out with a carborundum stone. Might end up making the rest look naff though.
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Sounds good to me , sharp varies across the country , not trained at college but can never understand the strong mix I've seen commonly used , softer as you go out , basic principle that's why its bad practice to used a steel trowel after sponge , same as skim and splashing water , produces hard surface prone to cracking and paint lifting from moisture barrier , skim surface should be flat with small pores ,
Now very curious if you agree with my theory of thermal shock to expose future cracking before filling and painting , haven't met a decent renderer for a very long time , solo worker so have no exposure to others to judge ( all the ones I've met were sh.t , )
 
An update on thermal shocking

Connect hose to coil of underfloor heating pipe ,
Put in tub of iced water
Keep the out hose short as possible and the end as close as possible to the wall , if you spray then the water droplet will heat up passing through warm air
The greater the temperature difference the better is what your trying to achieve
 
superspread said:
Yea ok, I can only tell u what I’ve found in 37 years of plastering, I’ve had it happen to me , even on my own extension, and trust me , I sbr slurried the blockwork and while still wet applied scratch coat with waterproofer in it, I even threw fibres in the scratch ( something I’ve never done before) , cured the render for days , and I stil got cracks , all pretty sound but cracks nevertheless, definitely thermal movement
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Theirs cracks and crazing mate two different issues
 
Lox said:
? What’s the process?
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Connect water hose to a coil of underground heating pipe and the another short length of hose on the end
Fill a tub with iced water and put the coil in
Now hose the wall down on a hot day
The hot or warm render gets thermal shock and reveals more cracks or crazing
Then its safer to fill and paint , best of a botch render
 
Havagojo said:
I'm pleased your back ,
Its to give it thermal stress and hopefully show any cracking which nay occur after you painted and the weather chops and changes in extreme
I expect a few more cracks to appear but better now before the paint
You said it was sound and I'm sure it'll be OK
Stress it , fill it , paint it , never had to try this before , lol but its no bother to hose a wall on a hot day in comparison to attempting to fill or cover straight off , what do you think
Click to expand...
Surely the crazing has occurred due to poor suction control and mix ratio and additive mix ! Nothing will change this after the set or show further weakness as it’s suction control hence the crazing which occurred during the set
 
Lox said:
Surely the crazing has occurred due to poor suction control and mix ratio and additive mix ! Nothing will change this after the set or show further weakness as it’s suction control hence the crazing which occurred during the set
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Do you not think their are stresses throughout the render that could expose themselves with future weather changes
 
Havagojo said:
Connect water hose to a coil of underground heating pipe and the another short length of hose on the end
Fill a tub with iced water and put the coil in
Now hose the wall down on a hot day
The hot or warm render gets thermal shock and reveals more cracks or crazing
Then its safer to fill and paint , best of a botch render
Click to expand...
For me your missing the issue mate ! The crazing I repeat crazing is a suction issue not thermal movement! The render is now set thermal movement requires the substrate to heat up and cool down differently to the render and can’t be shocked with a bit of cold water as it wouldn’t get through to the substrate
 
Lox said:
For me your missing the issue mate ! The crazing I repeat crazing is a suction issue not thermal movement! The render is now set thermal movement requires the substrate to heat up and cool down differently to the render and can’t be shocked with a bit of cold water as it wouldn’t get through to the substrate
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It's very late , been a long busy day will read again in the morning and talk tomorrow if that's OK
 
Lox said:
For me your missing the issue mate ! The crazing I repeat crazing is a suction issue not thermal movement! The render is now set thermal movement requires the substrate to heat up and cool down differently to the render and can’t be shocked with a bit of cold water as it wouldn’t get through to the substrate
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I totally agree with crazing being a suction issue not a problem but thought a wall that's had a few days of hot weather and so suddenly the top layer is cooled quickly would simulate future weather extremes and effectively test for future cracking
Promise I'll leave it their if you want cheers
 
thee_catfish said:
Hi peeps
Just rendered an extension and it has all crazed as it dried. None seems to have blown, just hairline cracks. What would be the best way to sort it without hacking it off. Client is going to paint it himself but I need to sort it first. Tia
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It’s dry shrinkage if it looks like this
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a few coats of paint should cover it.
 
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