TrowelADDICT said:
so your say...... if sand the wall down in a circular motion with 60 grit sand paper until all the shine has been removed and then apply a coat pva and skim, the plaster will fall off.
no mate, and theres no offence intended to your painting knowledge here..
what im saying is there is a hell of a lot more chance of the plaster falling off than if it was either gypbonded or keyed up better such as with a devil float..
pva the wall, let it tack up... what your plaster is gonna stick to is the pva, the pva is gonna stick to the wall.. sort of..
were talking about advise in general, the other day i advised a bloke in a similar situation to just quick devil float it and wack one thick coat on cos he'd asked about the quickest way round the problem..
my advise in this instance was based on what i believe to be the best way..
as far as im aware, pva is a sealer / bonding agent... chippies use a form of it to glue joints BUT where its good at its job is where there is some suction to pull it in.. I dont think the manufacturers would recommend pva to bond sealed surfaces like plastic / formica etc...
That would mean that theres a chance that the pva would de-bond from the gloss... bringing the plaster with it... it may not do, but theres a good chance... that post about the flats / hallway was a good example...
TrowelADDICT said:
chris w read this post u write about skimming on silk mate (which is a shine surface)
nah christ mate 25m is a big ceiling on yer own, i feel it, i do a max 30 on walls..
so...are we sayin then, that pva supplies a key...i tend not to notice too much difference if it HAS dried, in fact ive skimmed over well dried silk paint without pva and its gone lovely...
they go on about tricky timing on gypsum site..maybe this is why yes?
im a bit p"""d myself btw pug

in other words my theory bout needin suction is bollox? could be right including all the info...
I remember skimming a small silk painted ceiling with multi last year... If i remember rightly that is the job i was referring to...
well old house, but what i did notice was the fact that the multi didnt go all cheeselike as it would on gloss... im not a painter but from what i could gather there must have been some suction, albeit a small amount, i had 3 walls with it and had the ceiling in one coat so it wasnt like i was back on it straight away anyway..
it did behave like pva'd matt paint though... now i dunno if thats anything to do with silk being water based and gloss being oil based or what, youd be the man to answer that one, that was just my experience... ive had other silk jobs that have behaved like gloss and really wanted wba..
gloss paint however, different animal, ive had a few attempts at having gloss painted reveals in the past without a key or any prep and had a nightmare every time...
anyway, context of that post was a debate over whether to pva day before and let it dry? or was it about wba? all about the 'key' anyroad..
pva will liven up when you wet it if its dried.. (not waterproof pva obviously).. solves the 'dry' pva thing..
pva as a bonding agent over a gloss surface... knowing what i know now, i wouldnt recommend it..
youre 'polymer based' stuff like wba, gybond or bostic glue are designed for smooth shiny surfaces like gloss paint, or model aircraft kits... you wouldnt stick a model aircraft together with pva..
i could be wrong on a few points but if i was that far out, then there would be no need for products such as wba as plastering onto tacky pva whatever the surface should do the job perfectly well.. the fact that theyre available in the first place should say something in itself..
Im only going off my own experience and information ive picked up along the way..
first time i used wba was last year, on recommendation from this forum...
only my opinion.... no offense intended mate, i dont know how we'd go about proving either theory in any case.. it would need a chemistry expert i suppose? or ask british gysum?
I have been known to talk bollox from time to time... ;D