To use PVA in paint or not? That is the question.

Painting and decorating, plaster mouldings, Artexing questions

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bobbie-dazzler
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Post by bobbie-dazzler » Wed Mar 25, 2009 7:22 am

diybelle wrote:From talking to friends and from my own experience it is the plasterers that recommend sealing new plasterwork with PVA prior to painting so this is where it probably starts.

You are so right belle, its the plasterers that are the culprits :boxing: as nearly everyone who has the wonderful idea of using PVA on new plaster, has been told by thier plasterer.

It might be an idea also to have another sticky telling the posters how to get the PVA off new plaster walls and start again. ::b
I would rather want something I dont have, that have something I dont want
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Post by Susannah1 » Wed Mar 25, 2009 2:37 pm

darrenc wrote:I was wondering the same inver, probably started by a company that makes PVA! It must be one of the most common fallacies in painting, be nice if they could put on the tin something like ' not for sealing walls prior to painting ', would save alot of people alot of hassle, dont think it`ll happen tho :cb
Already happened -


Wickes Pva -"Do not use as a primer for paint".

Dulux dec centres Pva "Don't use under water based paint".
darrenc
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Post by darrenc » Wed Mar 25, 2009 3:21 pm

Thats good to know susannah :thumbright:

DIY Belle thin your emulsion by around 30%, no less as the porousity of the plaster must be satisfied to seal it
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Post by GC2decor8 » Thu Mar 26, 2009 12:43 pm

Well, what can I say........... :thumbright: ????????

I am soooooo glad I signed up to this forum on the recommendation of my bruv-in-law (Cheers Bruv if ur reading this!!). Thank you all so much for your varying degrees of advice, it is much appreciated.

I will consign myself to the drawing room and consider painting lines. "I must not use PVA, I must not use PVA" :lol: :lol: :lol:

I suppose a remedy for a PVA painted room is to restrip back to plaster and start all over??? Trouble is gotta remember which rooms have done in PVA now ::b ::b .

Now where's that receipt for the tin of PVA I brought last year......... :cb
diybelle
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Post by diybelle » Thu Mar 26, 2009 4:41 pm

darrenc wrote:Thats good to know susannah :thumbright:

DIY Belle thin your emulsion by around 30%, no less as the porousity of the plaster must be satisfied to seal it
Thanks I will keep a note of this mixture for the future.
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Post by john,mandy » Fri May 15, 2009 1:53 pm

Thanks for the tip about mixing paint and water :lol: I was always told to use a 50/50 mix ::b
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Post by Andrew » Sat Jun 13, 2009 12:45 pm

If everyone says you have to use non-vinyl paint for mist coat and everyone takes Dulux's recommendations, then why on the ICI trade site does it say, for dulux trade vinyl soft sheen: "Thinning - Brush or roller application: for sealing new or bare surfaces, 1 part clean water to 5 parts paint."

?

I'm going to be painting my kitchen this after plastering it, using a thinned down coat as recommended. Wrong?
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Have Brush Will Travel
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Post by Have Brush Will Travel » Sun Jun 21, 2009 9:16 pm

Never never never use PVA as a base for paint on new plaster..and ive never heard of mixing it with the first coat either

But....

Living up to my 'decorating maverick' name.... :?

Heres one that has always worked for me...

I have come across quite a few unpainted Artexed, nicotine stained lids over the years..impossible to wash down withought wrecking the Artex..

You can use specialist paints like Clissidur etc..but they are costly and stick to high heaven

Theres an easier way...either brush or use a garden spray a coating of thinned out bleach over them and allow to dry for a day, the bleach will help knock the guts out of the stain...then mix PVA with the first coat of
paint, (thinned slightly by about 15% to soak into the Artex) allow to dry thoroughly and then apply the second coat..if your using silk then you can add some more PVA to it..if your going for a matt finish then you cant do it as the PVA could leave a sheen

It always works for me and a few others I know of..

I dont read take a break for nothing you know!! :wink:
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Post by trowel monkey » Fri Jul 17, 2009 4:37 pm

well no plasterer i know would recommend using PVA on fresh plaster unless of course he was going to skim it again.

bad advice! these things get taken as read and passed on without anyone finding out the science behind it or if in fact it's true.

i've just plastered a room in my house, used the cheapest white MATT emulsion i could find, nothing special and watered it down 25-30% any more and it ends up on your floor, after one coat of this i used it neat for a second coat, after 2 coats it was ready for my chosen colour or a 3rd coat on the walls i left white.

JOB DONE!

vinyl will only work like PVA and seal the plaster, and if painted too soon it won't breath and let the moisture out and this will lead to problems later.
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Post by john,mandy » Fri Jul 17, 2009 4:46 pm

:hello2:

Soz to inform you but iam married to a plasterer and he does not recommend using pva on fresh plaster and doesn't no of any plasterer who would suggest that :scratch:

so the idea came from some other trade who probably doesn't like decorators :laughing3:

mandy
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Post by cwplastering » Fri Aug 07, 2009 4:51 pm

been on a job where ive had to repaint after the customers had the paper off..

one wall was scabby so i gave it a quick one coat skim (im a plasterer, im not going to fanny about with 2 coats and 3 hours when a quick pva and a sliver of multi will have it bang on ready for next mornings paint)..
rest of the walls had a wash down then a good rub with aluminium oxide..
not being a painter i just wacked a neat coat on the prepped walls in wickes vinyl..
skimmed wall got a mist off what what left in the tray after i did the ceilings (white matt, added some water)

problem i got was with the old walls and the new vinyl... went all bubbly in places so i left it overnight...
came back this morning and most of it had gone, just one bubble/blister so i scraped it and sanded it and stuck some white on it...
gave all the walls a coat of vinyl...
same thing happened to the old walls...

new one went luvverly...

came in here to ask what the problem was...

seems to be that the old walls got a coat of pva prior to paint on the new plaster (at the time)... would that be the correct assumption?

i told the customer that the old walls didnt get a mist coat, just straight vinyl..

could it be that also? or one or the other?

or something I havent considered?

ta for any help...
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bobbie-dazzler
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Post by bobbie-dazzler » Fri Aug 07, 2009 6:33 pm

chrisw w wrote: problem i got was with the old walls and the new vinyl... went all bubbly in places so i left it overnight...
came back this morning and most of it had gone, just one bubble/blister so i scraped it and sanded it and stuck some white on it...
gave all the walls a coat of vinyl...
same thing happened to the old walls...

new one went luvverly...

came in here to ask what the problem was...

seems to be that the old walls got a coat of pva prior to paint on the new plaster (at the time)... would that be the correct assumption?

i told the customer that the old walls didnt get a mist coat, just straight vinyl..

could it be that also? or one or the other?

or something I havent considered?

ta for any help...
The old walls could have been painted with PVA, or the old walls,(walls you didnt skim) could have had silk as the existing paint.

I never use paint from the can, I always thin down, even if its just 5-10%, specially going over old walls.

I'm thinking if it was PVA on the old walls, then the paint would have peeled off in sheets :scratch: it usually does.
I would rather want something I dont have, that have something I dont want
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cwplastering
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Post by cwplastering » Fri Aug 07, 2009 9:06 pm

when you say the old walls could have had silk as the existing paint.. youre right they were...
but do you mean its not ok to paint over silk or that the 'mist' or first coat of these walls was done with silk... as in vinyl?
what confuses me is if the existing vinyl paint has 'sealed' the wall, how come it bubbled up?

gettin into it a bit deeper...
im guessing paint needs 1 of 2 things to stick...
either suction (porosity) or a physical key (sanding)
same is true for plaster, pva only slows down the suction.
Theres another school of thought in plastering that says '1st coat of pva to seal, 2nd coat apply when tacky to stick the plaster to the wall'
unless its waterproof pva, the plaster will live the pva up anyway soon as it touches it..
completely killing the suction and not providing a key will leave you with hollow plaster in extreme circumstances, theres products designed for this instance with grit in them..
so im guessing a mist coat of a matt paint will slow down the suction enough for a silk paint to take hold before the wall sucks all the water out of it... bit like pva'ing a wall before a reskim?

maybe its got something to do with the 'V' in pva standing for 'Vinyl'?

thing is, as in plastering, its got to be one or the other, it cant be both? or can it?
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pva in paint

Post by marsal22 » Thu Aug 13, 2009 8:54 pm

Hi all

I agree with the do nots, never put pva neat or thinned into paint, the surface tension of pva [glue] and paint are completly different and as they dry, the surface skin can, as rightly already mentioned, dry against each other and cause fine cracking to paint,a bit like the effect obtained when using crackle glaze.

If pva was meant to be in paints it would already be in it

Also if you have pva already on plastered walls then use a contract emulsion from one of the leading brands, as these products do not react with the pva as these paints dont have vinyl in them.

hope this helps marsal22
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Post by Have Brush Will Travel » Thu Aug 13, 2009 9:41 pm

If pva was meant to be in paints it would already be in it

Sorry mate but its already in it and has been for years as he binder for many water based paints..including emulsion...thats why I use it in vinyl silk over unpainted artex that is nicotine stained*...it holds the stain back.

*(after a going over with a weak bleach/water mix using a garden spray)
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