Plaster srinks apart

[wese]

hi guys and gals,

having a few issues with my plastering and is really getting me frustrated,

basicly after applying plaster to wall,i get what looks like the plaster moving and showing gaps,looks like cracks,but is not cracks as it happens while the plaster is still wet.

once it goes like this its hard work,as i cant trowel over it,as the plaster just slides of the wall,the way i get round it,is to let it go off more then work it,


some have already told me to let glue dry more,have done this,but still happens,as the water in plaster just makes the glue wet again,

any more suggestions please

cheers

 

[GarethSullivan]

the only time i've ever encountered this is when i've just PVA'd a wall and i'm putting a thick skim over the top, even then it sags but doesn't crack like yours.

what are you plastering on top of?

Gareth

 

[noseall]

this is clearly a background problem like glossed walls or something?????

 

[roughcaster]

If you are spreading onto PVA that's too wet,and it gets mixed up into the plaster itself and tightens it up, it wont spread the same, it becomes "chewy and tough", and just slides over the surface and can slump. You can see the PVA in the pics, although I've never seen it split that way before, (said the vicar to the actress ) Did the splits appear as you trowelled up the wall or as you trowelled down, or neither, they just appeared? Just for interest, mix a small amount of plaster, pour a drop of PVA into it and mix it in and see how dead it becomes... I think it could be the cause, but that's just my opinion.

Roughcaster.

 

[wese]

it was plastered on top of original plaster,which had sand,cement underneath

this not the only time its happened to me,each time was on sound background,no gloss etc

roughcaster i followed advice of a fellow plasterer who said let glue go really dry,and same thing happened, so dont think its down to glue to wet


the splits appear by themself,just after ive applied to the wall,while waiting to go over it again,


from seeing it in the flesh,its looks like the glue has gone really wet again,the the plaster is srinking and pulling away from itself it different places,

because of how wet the glue is,i cant go over it again ,as it just slides all over the wall


cheers guys,

aghhhhhhhhhhhhh

 

[roy c]

I think that you've put the unibond on and skimmed it before the unibond has gone "tacky" and also maybe played about with the skim and not left it long enough before puttin on the second coat (if you did put a second coat on?) Its all about timing, and knowing when to apply the plaster and when to trowel up and when to leave alone.Just slow everything down,and maybe practice on a plasterboard and see how long you can leave the plaster and get an idea of setting times and take notes of reaction to putting it on top of unibond and leaving the unibond to go tacky and what happens when you dont. Also wet your trowel when polishing ,not the plaster..
Good Luck "Rome wasn't plastered in a day"

 

[Richard C]

I know its skim over original plaster/render but what finish is on the walls your plastering over, is it vinyl gloss or oil based paint?

 

[wese]

oil based paint? now that is a good question,im not 100 per cent sure,defo not vinyl gloss,and was a matt finish paint,but wether it was water or oil based not sure,that could be the problem i guess,

roy c ,i always let it go tacky buddy,and as i said before,ive let it go dry and firm,and still happens sometimes,so dont think its a question of my timing wrong,

im ok with my timing,i earn my living from it,so im no diy'er to plastering,so i like to beleive im doing it right lol

this as been happening before i have even gone over it again,so not down to playing with it,its happening while im waiting to go over it all once again



it must be a background problem,never happens on plasterboard

how would i know wether paint is oil based,can you tell by looking at it at all,can tell the difference between matt and vinyl no problem

cheers

 

[noseall]

plaster will only behave like that when it encounters very low or zero suction.

almost like plastering a metal wall.

 

[wese]

i can see where you are coming from on that noseall,nothing i can do i guess,will be hard to guess what walls will be ok or not,

cheers

 

[Richard C]

how would i know wether paint is oil based,can you tell by looking at it at all,can tell the difference between matt and vinyl no problem

cheers

It should be easy to tell but it doesn’t really matter as both will give problems with very low suction & poor adhesion unless properly prepared. I get the impression this is not the first time youve had the problem, how often has it happened?

 

[wese]

thinking back now,not many,prob about 5 times,but in saying that,the paint finish has been similar,not a matt finish,but not vinyl either if that makes sense,

and has always been council or ex council houses,i could take a pic of the wall im doing now if its of any use for you to see,if you could tell just by a pic,think it would be hard to see,compared to seeing in the flesh though

 

[roy c]

In all my years of plastering I have never encountered this problem... So the answer is in your preparation. When you prepare surfaces like you are explaining are you putting on the unibond and leaving it for 24 hours? Then another coat before you skim and letting it pick up? Also add some sand to your unibond on your first coat ........

 

[wese]

roy c,im not leaving it 24 hours to dry fully,plastering same day,but just waiting a little longer for it to go past the tacky stage,so its firm to touch


tryed this after some others on here suggested i leave it to go dry,still happens,hence why im back again,for advice,its a right pain,

the thing is,it does not happen all over the wall,its usally one or at the most two small areas on one wall at any time

cheers,

 

[roy c]

What type of pva are you using and what ratio are you mixing it? And how are youapplying it to the wall?