Rendering and pva?

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spark2010

New Member
Can someone here please finalise this topic once and for all. On my course I was told never use PVA with rendering, just dampen with water... on the other hand I hear experienced plasteres saying they have been using PVA for rendering for years and no problems. i thought that PVA creates a skin therefore the render would crack and eventually fall off the wall. On a tub of PVA it states not to be used externally? Also There is a training company called Gold trowel and they have a load of DVD's on plastering, rendering etc and it shows the guy on there PVAing outside houses and then rendering them and before pebble dashing also .... so

What is the story here...
Can PVA be used on external rendering?
can PVA be used in internal (ext wall) rendering?
 

plasterjfe

Private Member
simple, if it says on the actual pva NOT FOR EXTERNAL USE then take that as gospel because they aint gonna put their name to saying it can be used. dont listen to anyone telling you they done it for years with no problems. how would they even know there was no problems unless they went back to every job every year to check? dont take the chance.

Once and for all NO its not for external rendering

If you walkd across a frozen pond in winter and you never went through and drowned, does that mean we can go walking on frozen ponds with no problems!
 

beddy

Well-Known Member
i saw the rendering dvd and was suprised when he used pva. the way i see it is if pva says dont use it externally, then i dont. sbr isnt that much more expensive and it gives you peace of mind.
 

spark2010

New Member
ok so thats a no then... thanks.

I looked at the link on the above post, waterproof PVA, so thats probably what people are talking about when rendering.. but i was told just dampen with water and it will be fine!!!!!!
 

gitznshiggles

New Member
From my limited knowledge it goes like this.

PVA for suction control on internal walls and ceilings - mix varies from person to person - skim on when tacky
Bonding agents like WBA on internal walls and ceilings for mechanical key, better to use also on artex instead of pva
SBR etc for external jobs like rendering

please correct if wrong
 

spark2010

New Member
From my limited knowledge it goes like this.

PVA for suction control on internal walls and ceilings - mix varies from person to person - skim on when tacky
Bonding agents like WBA on internal walls and ceilings for mechanical key, better to use also on artex instead of pva
SBR etc for external jobs like rendering


please correct if wrong

yes that sounds about right... thing is my Where i work i sell UNIBOND SUPER PVA in the red tub, I was reading it and it said for render and on the back was ratios for plastering, rendering etc... It also says on the front interior use.
So i take it there talking about internal rendering.. its so confusing

is there a difference between PVA and SUPER PVA?
 

Render Systems

Private Member
I have never used PVA externally and never will... as for EVA i have never used that either, i just damp the substrates down with H2o and if there is a difference in the substrates in the olden days i used to put eml over the joins to prevent cracking... nowadays we use TV10 mesh...
top tip if the substrates are porus soak them with water so that they appear damp and not dripping wet then apply scratch coat... thats all you need to do unless using monocouche or OCR and the spec says to use a primer...
 
as ever, read the label... they cant lie! who you gonna trust someone in teh pub that says ah it will be ok or the company that manufacture it and test it :)
 

spark2010

New Member
as ever, read the label... they cant lie! who you gonna trust someone in teh pub that says ah it will be ok or the company that manufacture it and test it :)


lol, ya render systems looks a bit of an alco actually
but what do you use? do use PVA dan?
 

flynnyman

Well-Known Member
PVA is ok to use outside to seal any dust but not as a bonding agent or to provide any key there are other products on the market for that.
 

spark2010

New Member
You see, i dont think anybody really knows, I personally am never going to use PVA outside, I know a guy when plastering years and like you said Danny, he uses SBR
 

Pug

Well-Known Member
mix it up as a slurry with sand and cement and paint it on. thats what i do anyway.
 

Freerider

Member
To be honest none of it makes any sense to me, I dont see the harm in using it if its just for suction and dust contamination, thing I dont get is if the reason you shouldnt use it is because it creates a barrier then that is total b*ll***s..

If they say you can use waterproof PVA outside then how does that work, if anything was to create a barrier it'd be the waterproof PVA becuase once its gone off it wont come back to life again once you start plastering, so surely normal PVA doesnt create a barrier what so ever, in reality it just sits there blocking a bit of the suction.

As far as I am concerned, just becuase it says on the back of a product "dont use" doesnt always mean its right, half the time they say this just so you buy yet MORE of their products, example.. british gysum "dont tile on backing plasters", why? "due to the suction", "so buy some finish off us instead and use twice as many materials then its ok :), since when have backing plasters if controlled had more suction than skim, load of b*ll***s!

However I am not saying you should use PVA outside, but you see what I am saying!
 

spark2010

New Member
To be honest none of it makes any sense to me, I dont see the harm in using it if its just for suction and dust contamination, thing I dont get is if the reason you shouldnt use it is because it creates a barrier then that is total b*ll***s..

If they say you can use waterproof PVA outside then how does that work, if anything was to create a barrier it'd be the waterproof PVA becuase once its gone off it wont come back to life again once you start plastering, so surely normal PVA doesnt create a barrier what so ever, in reality it just sits there blocking a bit of the suction.

As far as I am concerned, just becuase it says on the back of a product "dont use" doesnt always mean its right, half the time they say this just so you buy yet MORE of their products, example.. british gysum "dont tile on backing plasters", why? "due to the suction", "so buy some finish off us instead and use twice as many materials then its ok :), since when have backing plasters if controlled had more suction than skim, load of b*ll***s!

However I am not saying you should use PVA outside, but you see what I am saying!

Thats a good point actually especially about the tiling onto backing plasters
 

layiton

Member
To be honest none of it makes any sense to me, I dont see the harm in using it if its just for suction and dust contamination, thing I dont get is if the reason you shouldnt use it is because it creates a barrier then that is total b*ll***s..

If they say you can use waterproof PVA outside then how does that work, if anything was to create a barrier it'd be the waterproof PVA becuase once its gone off it wont come back to life again once you start plastering, so surely normal PVA doesnt create a barrier what so ever, in reality it just sits there blocking a bit of the suction.

As far as I am concerned, just becuase it says on the back of a product "dont use" doesnt always mean its right, half the time they say this just so you buy yet MORE of their products, example.. british gysum "dont tile on backing plasters", why? "due to the suction", "so buy some finish off us instead and use twice as many materials then its ok :), since when have backing plasters if controlled had more suction than skim, load of b*ll***s!

However I am not saying you should use PVA outside, but you see what I am saying!

Tile adhesive dont stick well to browning/hardwall to well
 

plasterjfe

Private Member
To be honest none of it makes any sense to me, I dont see the harm in using it if its just for suction and dust contamination, thing I dont get is if the reason you shouldnt use it is because it creates a barrier then that is total b*ll***s..

If they say you can use waterproof PVA outside then how does that work, if anything was to create a barrier it'd be the waterproof PVA becuase once its gone off it wont come back to life again once you start plastering, so surely normal PVA doesnt create a barrier what so ever, in reality it just sits there blocking a bit of the suction.

As far as I am concerned, just becuase it says on the back of a product "dont use" doesnt always mean its right, half the time they say this just so you buy yet MORE of their products, example.. british gysum "dont tile on backing plasters", why? "due to the suction", "so buy some finish off us instead and use twice as many materials then its ok :), since when have backing plasters if controlled had more suction than skim, load of b*ll***s!

However I am not saying you should use PVA outside, but you see what I am saying!

PVA re-emuslifies when it comes into contact with moisture so it cant be used outside because it will loosen up and move in turn shifting the products that it lies between. nothing to do with it being uncompattable with the render product, you need a a product that once cured stays cured, sbr allows more passive suction also giving the render a better chance to adhere.
this is first lesson in college about rendering.

hopefully we can move on
 

The Apprentice

Well-Known Member
Why use PVA to control dust and suction when water will do exactly the same and water is free and comes out of the end of a hose pipe quicker and easier than brushing or rolling PVA.
 

plasterjfe

Private Member
ITs gonna debate forever,

I do what I was taught in college and from guys I worked with who had years of experience and I follow the spec on modern stuff its that simple.

Many People will just do whatever I suppose, thats life
 

lucius

Well-Known Member
Acetic acid which is formed when when cement and PVA comes into contact either by mixing or priming will continualy free the water bound in the cement which will weaken the bond and./or the integrity of the material. The affect is accelerated if the material is subjected to moisture which is more or less always the case.
PVA isnt water resistant it becomes live when when exposed to moisture and this combined with the exposure to Alkali accelerates the forming of Acetic acid.
PVA which is marketed as water resistant or exterior has additives to make them so but they are not Alkali resistant.
This info has been posted on this forum before in one form or another jut thought i would post it again.
 

Freerider

Member
Why use PVA to control dust and suction when water will do exactly the same and water is free and comes out of the end of a hose pipe quicker and easier than brushing or rolling PVA.

pva is a much better way of getting over dust contamination and thats a fact, means you can pva chases etc/ and dont have to hit em whilst the water is still wet, or pva a whole room before floating, theres no argument where thats concerned!

and plasterjfe, your right dude, you have made me understand a bit better now to why its wrong! I never debated you shouldnt use it as such, just didn't know the exact reasons, so as many do, question if it really is bad/good or whatever!
 

The Apprentice

Well-Known Member
pva is a much better way of getting over dust contamination and thats a fact, means you can pva chases etc/ and dont have to hit em whilst the water is still wet, or pva a whole room before floating, theres no argument where thats concerned!

Maybe not but you then should apply plaster while the PVA is tacky. PVA is no better than water for removing dust than water, and that is also a fact. Not sure why PVA would be better other than when its being brushed on and it will remove more dust then but you can do that with a water brush as well.
Far to much emphasis put on PVA, even seen PVA being put on hardwall that only went on that morning.
 

Freerider

Member
why should it be applied when tacky, your not using it to stick the plaster to the wall on float coats are you. It is much better for dust contamination, water is useless unless you plaster on it there and then, but **** it whatever!
 

flynnyman

Well-Known Member
Using excessive water is frowned upon coz a building needs to be dry before plastering using pva your not really removing the dust your sealing it and its not being used as a bonding agent.
 
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