second coat of render

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ironmonkey

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evening all,quick question about top coat render.I laid up first coat before christmas and the the weather came in,i am going to second coat this week,my question is whether to damp down or uni-bond first coat to control suction.What do you think?
 
I allways pva between coats, it guarantees uniform suction.

Ten quid someone comes on and says - throw snow at it to wet it down ;D
 
nelly said:
I allways pva between coats, it guarantees uniform suction.

Ten quid someone comes on and says - throw snow at it to wet it down ;D
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Don't need anymore snow,jobsite still thawing out after 3 weeks under it.Thought the pva route would be best but needed a second opinion.
 
McPlaster said:
If it's not too big of an area bit of suction can be nice and rubs up sooner mate.
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2 chimneys,2 seperate scaffs so a fair bit of running around so i wll need a bit of time and will need to reduce the chance of cracking as wont be able to access once the scaffs come down.
 
ironmonkey said:
evening all,quick question about top coat render.I laid up first coat before christmas and the the weather came in,i am going to second coat this week,my question is whether to damp down or uni-bond first coat to control suction.What do you think?
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do both mate, give it a good soak down then pva it. did you use waterproofer in the first coat?
 
Personally i'd just wet it down...you don't want it going off to slow...its going to be slow enough in this weather...otherwise you risk floating in the dark.
 
Why would any one use wood glue between coats of exterior render, beats me sometimes where you blokes get your info from.
Lucius
 
I am with lucius i wouldnt pva it do a test panel see how much it pulls in if its still wet after 5 mins you should be fine to bang it all on a light wetting dont hurt either.
 
pva shouldnt be used externally and if youve put waterproofer in the scratch then a bit of water is all youll need at most, at this time of year lack of suction wont be a problem
 
i was always taught never pva with sand and cement

would only give it a wet down if its windy or sunny if left a while.

otherwise just chuck it on and get done
 
if youve got waterproofer in the scratch youll likely still be there at 10pm in this weather anyway...
 
lucius said:
Why would any one use wood glue between coats of exterior render, beats me sometimes where you blokes get your info from.
Lucius
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I understand what you are saying,the bloke i work with has been rendering and plastering for about 30 years and has done it all,the first coat went on three weeks ago and so we dont have to go at it like idiots and risk ballsing it up he suggested a coat of pva to give us time to get it on straight and correct and so the PAYING customer gets a perfect job without the worry of a return visit.Just thought i would see if it would work.Thanks for the other helpful replies chaps.
 
lucius said:
Why would any one use wood glue between coats of exterior render, beats me sometimes where you blokes get your info from.
Lucius
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next time you pick up a tub of PVA read the directions for rendering on the back of the tub :)
 
Just put a little water on and then hit...don't take your time just get it all on the wall as quickly as possible...if you don't have it all on the wall by 11am expect to have the van parked with the lights on it...if you put PVA on it take a tent with you.
 
Just put a single light brush of water on a couple of different areas to check for excessive suction (unlikely this time of year), remember a bit of suction is a good thing with rendering and as long as you use an appropriate mix and keep the thickness correct it won't cause cracking and will help with adhesion.
 
essexandy said:
Just put a single light brush of water on a couple of different areas to check for excessive suction (unlikely this time of year), remember a bit of suction is a good thing with rendering and as long as you use an appropriate mix and keep the thickness correct it won't cause cracking and will help with adhesion.
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Thanks mate
 
nick0412 said:
i was always taught never pva with sand and cement

would only give it a wet down if its windy or sunny if left a while.

otherwise just chuck it on and get done
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Im with you on that one.
 
FreeD said:
Just put a little water on and then hit...don't take your time just get it all on the wall as quickly as possible...if you don't have it all on the wall by 11am expect to have the van parked with the lights on it...if you put PVA on it take a tent with you.
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Recon the lights on me van would struggle to illuminate the chimneys,i will suggest to the gaffer in the morning about binning the pva as the general rule seems to be to just dampen down.
Thanks anyway mate
 
kirk johnstone said:
lucius said:
Why would any one use wood glue between coats of exterior render, beats me sometimes where you blokes get your info from.
Lucius
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next time you pick up a tub of PVA read the directions for rendering on the back of the tub
I dont read it cos i dont need with rendering please tell me what the benefits of a water soluble wood glue have with outside rendering and i will give you twice as many reasons not to use it.
Lucius
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lucius said:
kirk johnstone said:
lucius said:
Why would any one use wood glue between coats of exterior render, beats me sometimes where you blokes get your info from.
Lucius
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next time you pick up a tub of PVA read the directions for rendering on the back of the tub
I dont read it cos i dont need with rendering please tell me what the benefits of a water soluble wood glue have with outside rendering and i will give you twice as many reasons not to use it.
Lucius
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you said you wonder were some of these guys get there ideas from, i got it from the back of the tub one time when i was having a problem with suction whilst pebble dashing. i worked for me. cant see what the problem is?
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The only reason to use PVA on rendering is if something has been/gone wrong in the first place and that can happen to anyone but it's madness to use PVA as a matter of course, I've seen it cause people problems on externals.
 
essexandy said:
The only reason to use PVA on rendering is if something has been/gone wrong in the first place and that can happen to anyone but it's madness to use PVA as a matter of course, I've seen it cause people problems on externals.
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av only done this once when i had a problem with suction, but just so i know for the future what problems can it cause mate?
 
kirk johnstone said:
essexandy said:
The only reason to use PVA on rendering is if something has been/gone wrong in the first place and that can happen to anyone but it's madness to use PVA as a matter of course, I've seen it cause people problems on externals.
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av only done this once when i had a problem with suction, but just so i know for the future what problems can it cause mate?
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I've seen render shell when PVA has been applied to a scratch coat which is not completely dry as it seals the moisture in, which has to get back out at some stage. Also by PVAing you loose the suction adhesion and a fair bit of the mechanical key, it's difficult to PVA a large area and still be working on it when it's tacky and once it's dried you'd be working on a glassy surface which ain't good. Hope that helps.
 
essexandy said:
kirk johnstone said:
essexandy said:
The only reason to use PVA on rendering is if something has been/gone wrong in the first place and that can happen to anyone but it's madness to use PVA as a matter of course, I've seen it cause people problems on externals.
Click to expand...

av only done this once when i had a problem with suction, but just so i know for the future what problems can it cause mate?
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I've seen render shell when PVA has been applied to a scratch coat which is not completely dry as it seals the moisture in, which has to get back out at some stage. Also by PVAing you loose the suction adhesion and a fair bit of the mechanical key, it's difficult to PVA a large area and still be working on it when it's tacky and once it's dried you'd be working on a glassy surface which ain't good. Hope that helps.
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How do it lose the mechanical key? the scratches are the mech key and pva-ing wont affect that at all.

And one coat of pva wont seal the moisture in..........two seperate coats would, but one wont.

I'll admit suction wont be a problem this week with the cold.
 
What was the Substrate ? If you used a descent sand and gauged the waterproofer , i would definitely not wet it down and even if you didn't i would think twice, and rendering this time of year wants to be on the wall by 10. 30 am mix it up as stiff as you can use it ,the wall my look dry before you start but once a bit of moisture gets on it from the top coat the waterproofer will start working and will hang around wet all day and make sure you have a good 1st coat key and push the top coat right into that key . Good luck and do you have any site light s ;D ?
 
church said:
What was the Substrate ? If you used a descent sand and gauged the waterproofer , i would definitely not wet it down and even if you didn't i would think twice, and rendering this time of year wants to be on the wall by 10. 30 am mix it up as stiff as you can use it ,the wall my look dry before you start but once a bit of moisture gets on it from the top coat the waterproofer will start working and will hang around wet all day and make sure you have a good 1st coat key and push the top coat right into that key . Good luck and do you have any site light s ;D ?
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Yeah mate,got a full set of festoon lights on standby..
 
kirk johnstone said:
ironmonkey said:
evening all,quick question about top coat render.I laid up first coat before christmas and the the weather came in,i am going to second coat this week,my question is whether to damp down or uni-bond first coat to control suction.What do you think?
Click to expand...

do both mate, give it a good soak down then pva it. did you use waterproofer in the first coat?
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Hmmm well now... young chap you shouldnt need to do anything to the scratch coat in this weather as it will be damp anyway. also you never put pva onto exterior render the suction should have been controled with a waterproofer in the scratch coat... also your method seems a bit ridiculous as if you did pva it and then watered it on to it would be like a bloody waterfall running down the wall old bean...
 
Cement is Alkaline which means it has a high PH, Alkali slowly attacks PVA forming Acetic acid which has a low PH. Cement cures through hydration which means it binds the water you mix it with chemicaly. This causes the PH to rise dramaticaly. Introducing an acid negates the hydration process to some extent preventing the cement from binding all the water it needs to harden properly.The Acetic acid which is formed when cement and PVA comes into contact will continualy free the water bound in the cement and will weaken the bond, even more so if subject to moisture.
PVA isnt water resistant it becomes slightly live when exposed to moisture and this combined with exposure to Alkali accelerates the forming of Acetic acid, PVA marketed as water resistant has additives to make it so but not Alkali resistant.
Stick that in your pipe and smoke it.
Lucius.
 
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