Hollow render

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bodplasterer

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Done a rendering job last year on a small extension and had to go back the other day as it has gone hollow :(, what i cant understand is it has only gone on one side we did it all round on new block work the same day and the rest is solid but right at the back it has blown there is a small hairline there as well, any one know how this could happen? cant get my head round it :-? I was thinking the sun might have gone on it? or some water might have got in through the hairline and frosted up but im sure we didnt get much frost last year and it was done in late summer.
 
could it be movement mate?
i hate render if you do it by the book it can still go pear shaped :mad:
 
Yeah didnt think of the movement could be but it. sucks that i have to go back and redo it for free :( Hopefully it has only blown on the scratch and can get away with just topping it again. I was speaking to a mate a while back and he reckons that 5:1:1 mix is too strong and he uses 6:1:1 apparentley stops cracking.
 
we use 3-1 scratch and 4-1 top coat fook knows but we can do k-rend by the book and it'll still blow, it's a nightmare mate i won't touch it on private work i'm scared before the job'll even start
 
i've officially banned my 3 year old and 10 month old from even walking next to my newly rendered garage .........for there own sake ;D
 
They have got a kid but its only about 6 months old, I just remembered this bloke told me once that if you rub up when its too wet it can blow off the wall, weather this is true im not sure? I do have a habbit of being too impatient and try and float up while its wet.
 
i was taught to float it twice mate but i know what you mean my bellcast areas have suffered half the wall was pulled down and sitting on them when i was floating !!
i think i'm suffering from a daywork crisis ;)
 
Hi mate, what blocks were they and were they 4 or 9 inch think,? also how thick was your coats of render ? and were abouts is the crack on the wall and does it run from a door or window? , i think outside rendering is the toughest thing to get right theres a lot of things to take into consideration and some of them like movement and exspantion are out of our hands.I dont think its right you have to go back and make it good especally if its proved to be not your fault.
 
This is the thing that gets me church the crack is horizontal across the back there is no windows and the area is only about 6m2 so no need for expansion joints the thickness of the render wasnt thick at all we are pretty tight on coats i would have said 10mm if that, i have done 100's of rendering jobs and this is just a one off me thinks..... just have to suck it in and re do it... talking of thickness i was working with a spread once and he told me you can learn alot from hacking a house off how much harder it is to get it off when the render is thin.
 
i would put money on the crack running along a block joint, let us know if you can, told you it wasnt your fault ;)
 
Hacked the back off the other day with ease only took 10 mins with a clawhammer turns out the scratch had'nt cured, it was all dusty and the topcoat was solid but still cant my head round why the side is solid im thinking the scratch was prob over mixed and went a bit fluffy and the sun was straight on it. It now has been rescratched yesterday and gonna top it sometime next week so should have plenty of time to cure. when we were half way through it the heavens opened up and i was just thinking this job is cursed but luckily it was just a quick shower and held off the rest of the day.
 
expansion joints heard of these for tiling large floor but for plastering? what sort of area would you be looking at to start using these...used for rendering on scratch coat? any data sheets?
 
I have been specified to put expansion joints in anything over 3 meters usually a back to back stop bead but you can get beads for purpose expansion joints, they are a lot easier to use as they are joined and you dont get the different levels you get by putting 2 beads back to back.
 
Pretty sure that the building regs state expansion joints should be at a maximum of 4m but its also important to put them on the backgrounds that will move differently.
 
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