WHAT MAKES PLASTER TEAR??

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Barzie

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Hi all. I HATE it when this happens- get over it in the end, but was wondering if there is any way of stopping it in the first place. What causes it???
:o
 
Barzie said:
Hi all. I HATE it when this happens- get over it in the end, but was wondering if there is any way of stopping it in the first place. What causes it???
:o
Click to expand...

if it tears early on then its to much suction, if it starts to peel when you are polishing then you aint letting the pva go tacky enough. if it peels on board then you probably aint putting it on thick enough mate

hope this helps ;)
 
i used to find it happens when its hot and you have your trowel on to much of an angle. hasnt happened in 3-4 years though.
 
loads of reasons for this barzie lad second coat going on too late (too long between skim coats)/ drying out too fast in summer this sometimes happens/ freezing cold weather this can happen/ bad batch of powder/ couldnt really say unless i was there. what you plastering onto
 
plasterjfe said:
loads of reasons for this barzie lad second coat going on too late (too long between skim coats)/ drying out too fast in summer this sometimes happens/ freezing cold weather this can happen/ bad batch of powder/ couldnt really say unless i was there. what you plastering onto
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Re-skims on PVA walls- it happens towards the end when trowling up wiv water............
 
kirk johnstone said:
Barzie said:
Hi all. I HATE it when this happens- get over it in the end, but was wondering if there is any way of stopping it in the first place. What causes it???
:o
Click to expand...

if it tears early on then its to much suction, if it starts to peel when you are polishing then you aint letting the pva go tacky enough. if it peels on board then you probably aint putting it on thick enough mate

hope this helps ;)
Click to expand...

Must be the PVA thing then mate, cos its always towards the end.
 
Barzie said:
kirk johnstone said:
Barzie said:
Hi all. I HATE it when this happens- get over it in the end, but was wondering if there is any way of stopping it in the first place. What causes it???
:o
Click to expand...

if it tears early on then its to much suction, if it starts to peel when you are polishing then you aint letting the pva go tacky enough. if it peels on board then you probably aint putting it on thick enough mate

hope this helps ;)
Click to expand...

Must be the PVA thing then mate, cos its always towards the end.
Click to expand...


that could also be because your trowel is new mate
 
kirk johnstone said:
Barzie said:
kirk johnstone said:
Barzie said:
Hi all. I HATE it when this happens- get over it in the end, but was wondering if there is any way of stopping it in the first place. What causes it???
:o
Click to expand...

if it tears early on then its to much suction, if it starts to peel when you are polishing then you aint letting the pva go tacky enough. if it peels on board then you probably aint putting it on thick enough mate

hope this helps ;)
Click to expand...

Must be the PVA thing then mate, cos its always towards the end.
Click to expand...


that could also be because your trowel is new mate
Click to expand...

Trowel is about 3 years old now
 
I think a change of a better quality pva is in order mate if its doing it on several different walls and your a capable plasterer.
 
roughly about 15-17 metres if watererd down a little bit but not much i love it me if ya can get in the day before or get ther early you can skim on it after 2 hrs but the longer you leave it he better really pva only works with 2 coats an i cant be arsed with all that just one coat of this gear an away you go
 
i wish people would understand the difference between bonding agent and pva... ::)

bonding agent is used on surfaces with limited or no suction, its not for suction control but to give a key to the plaster...
applying plaster onto a gloss painted surface without a bonding agent will have it blowing because all youve done is installed a 3mm thick wall of gypsum in front of the gloss paint....

now, pva is designed to be used where there IS suction...
you wouldnt use wood glue to stick two peices of plastic together, youd use something like bostik polystyrene cement...
pva is a great adhesive on things like timber because timber is porous, the pva soaks into the pores where it sets, it bonds readily to itself and other porous substances such as old plaster because theyre POROUS...

bonding agent will bond readily to non porous surfaces.... it contains a fine aggregate suspended in the solution which will then offer up a 'key' to your plaster, the plaster will wrap itself around the grains and be held in place..

bonding agent does offer some suction control properties but its expensive, and doesnt control suction even half as good as pva litre for litre...

you sometimes get away with pva'ing a shiny surface and skimming it tacky because the plaster will stick to tacky pva (even dry non-waterproof pva because the wet plaster will liven it back up again)..

people seem to think that pva is a 'glue' to stick the plaster to the wall...
its not, although controlling suction with a wet 5:1 mix and letting that dry followed up by a 3 or 2:1 mix and skimming it tacky will have this effect...
the first coat is to control suction, it does this by soaking IN to the wall, the second coat bonds readily to the first coat and also the plaster although there will still be SOME suction...

overdo the pva and youll kill ALL the suction and leave yourself with problems when using multi finish, all youll end up doing is trowelling the entire thickness of plaster round the wall until it starts to chemically set...

controlling suction (or lack of) is a tricky skill to master but as its been said before, its probably the most important thing a plasterer will ever learn...

its not essential to 2 coat a surface with pva either.....
think about it, you dont need to GLUE the plaster to the wall, the suction will hold the plaster in place, all you need to do is bring the suction down to a level that allows you to finish the surface properly (time)
hardwall and bonding dont need pva'ing if you hit them at the right time, this is because they offer up just the right amount of suction to pull the plaster in, in fact done correctly its probably the best bond youll ever get... same goes for render....

hardwall and multi finish where there is suction...

render and toughcoat where theres excessive suction...

bonding and board finish where theres limited suction...

plasterboard is classed as limited/medium/low suction...
moisture resitant plasterboard has NO suction, you have to treat it with a bonding agent first...
old plaster is medium to high suction..
old render is high suction...
old (over a day) bonding/hardwall/browning/toughcoat is all high suction...

pva for suction...

bonding agent for no suction...

am i in danger of repeating myself? ;D
 
very well explained.....as u say chris....if a plaster doesnt know this and about suction in general they shouldnt be plastering as this is pretty basic stuff.......but the building blocks of plastering!
 
Nice tip about the wba kirk,who told that ?
Tearing is nearly always down to the plasterers timing,if it starts to tear leave a little longer.
Nice words chris.
 
skimmin2day said:
Nice tip about the wba kirk,who told that ?
Tearing is nearly always down to the plasterers timing,if it starts to tear leave a little longer.
Nice words chris.
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erm am just sad mate and i like to read everything, sit looking at labels when i have my dinner ::)
 
kirk johnstone said:
it is also for friable surface's!
it says so on the tub mate ;)

https://www.wickes.co.uk/Plaster-Bonding-Agent/invt/221807
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fair enough it'll bond it together, that'll be the adhesive properties, i'd still be careful on high suction with it though...
tell you how i know... ive tried it thinking i could bang a full room on, reskim over old plaster......
f'ck me i was nearly crying towards the end.... ;D
lick of wet pva first would have helped enormously...
but then, thats just more messing around innit, keep it simple...
 
That wba certanly does hold the gear back for ages but you have to put a decent amount on not skimping at all with it,but then all of a sudden it starts to pull the plaster in really fast.
in the past ive put in on weaker to cut cost and watered it down etc,but to get the best results use neat with a good thick coat.
If the stuff was cheaper to purchase id definately use it more often
 
water down your wba with 5-1 pva, goes twicwe as far and best of both worlds.never tried this but a reliable source told me it works well.
 
skimmin2day said:
That wba certanly does hold the gear back for ages but you have to put a decent amount on not skimping at all with it,but then all of a sudden it starts to pull the plaster in really fast.
in the past ive put in on weaker to cut cost and watered it down etc,but to get the best results use neat with a good thick coat.
If the stuff was cheaper to purchase id definately use it more often
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try using board finish.... read through the thread and see why... trust me, it works...
the idea is it goes on a surface with no suction, it'll go a lot further then...
put it on something with no suction and youll use loads of it in a very small space cos the wall will just pull it in...
watering it down doesnt work....
knocking it up with some pva works better as kk said, but then, you may as well use pva and save yourself a tenner? or just give the wall a coat of wet pva first and let it dry, preferably waterproof pva... not forgetting that ordinary pva will liven up when you hit it with wet plaster wheras bonding agent doesnt..

unless, just maybe, as captain james t mentioned earlier, youve got a 'friable' surface where pva might cause you problems.. distemper residue for example but were into degree level plastering there and ill leave that to the chemists.. most people use a stabilising solution... cheaper...

maybe bonding agent is stabilising solution with grit in it? wouldnt that be a revelation? :o
 
Don't water down WBA, goes too thin no good, tried and tested and wasn't a happy bunny having to go over what I'd put on again with fresh costing another £14!! Bond it will take some water tho.
 
Barzie said:
kirk johnstone said:
Barzie said:
Hi all. I HATE it when this happens- get over it in the end, but was wondering if there is any way of stopping it in the first place. What causes it???
:o
Click to expand...

if it tears early on then its to much suction, if it starts to peel when you are polishing then you aint letting the pva go tacky enough. if it peels on board then you probably aint putting it on thick enough mate

hope this helps ;)
Click to expand...

Must be the PVA thing then mate, cos its always towards the end.
Click to expand...
i bought 10 litres of PVA from that big red supa store b&? it smelt like bad eggs, took it back they said nought wrong with it, room stunk and so did plaster finish, sort of curdled and dragged?
 
Thanks for your knowledge Chris w
so pva does'nt gule plaster it controls background suction, i dont want to bore you but should pva be wet, tacky dry before you plaster and is it necercery to pva on same day as applying plaster to walls or can you pva the day before
"recap" i mix pva 70% water 30% pva is this ok
thanks
 
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