cracks appearing in newly plastered wall - why?

[nicholas mayhew]

Hi

I would be very grateful for your help.

We plastered the wall under the stairs and in one section small egg shell-like cracks appeared the next morning.

The house is old (1750s), but the wall is at a guess Victorian (brick I think, but we did see sandstone like parts where we chipped a bit vigorously!)

Preparation:
- woodchip wallpaper steamed off, revealing perhaps 4-5 different paint layers; scraped and sanded off as best we could.
- diluted PVA applied a couple of days before
- PVA applied just before plastering (all standard ratios)

the wall after most of it has been prepped

this is the area where there are some cracks - you can see it was in a bit of state! the outer skirting board has since been removed

We are very slow, novice plasterers, so the PVA was probably bone dry in some areas by the time it was plastered.

The cracks look huge but are hairline or thinner when seen in real life. The ones in the photo are maybe 1 or 2cm in length (sorry must have got the camera zoom a bit wrong!)

Any thoughts on likely cause of the cracks?

What should we do to repair them, as 90% of the wall is sound.

And given our inability to plaster quickly, would we be better of with a Thistle Bond-It / Knauf Betokontakt type prep, rather than PVA next??

Many thanks for your help

Nicholas

 

[stevethespreader]

you would be better off with thistle bond it yes but that dosent mean that pva wouldent work on those walls , it looks like you dident prep it properly, either the pva wasent applied consistantly enough or the pva dident skin up, may i ask what make of pva you used?

 

[nicholas mayhew]

Hi Steve
I used Cementone Rendabond PVA which I bought from Homebase.
When thinned 5-1 for the sealing coat it really was like water (painted on - perhaps should have rollered?), but since this is our first effort I don't have anything I compare it to.
Even when 3 PVA to 1 water it seemed thin (to me).
Hope this helps?

Any thoughts on how we repair the cracks, or what we should do next time?

Many thanks

Nick

PS what does skin up mean?

 

[stevethespreader]

when you put pva on the walls and leave it it should form a skin sealing the wall, a lot of cheap pvas dont do this espec when you water them down, you cant water down cheap pva as much as you can the dear stuff, im not a fan of cementone i threw the last cementone tub i had away
i know someone on here that uses it though, rather him than me espec on paint, saying that ive just skimmed my room with a cheap pva over paint its that no nonses crap from b and q i found that to be watery as well
so i gave my walls 2 coats to seal it b4 giving it the tacky coat also i used a stronger mix than it said on the tub, ideally i would have used bond it or wba but i used 2 tubs of wba on my ceiling and i had the tub of pva in the shed so i used that, you have already said that it was like water, your mistake was not realizing at the time that its not going to do the job , you should have said to yourself that this is going on a bit weak and you should have put another coat on or even a stronger coat , instead of giving it just 1 watery coat, also you can look down the wall and it should be all shiny if it has skinned up also you will be able to see any misses , if that was my wall i would scrape it all off and start again, i bet it comes off really easy

 

[nicholas mayhew]

thanks for the clarification Steve, much appreciated

if i can ask about minor imperfections and small pits in our finish (not cracks due to poor prep): can we apply another coat of plaster over the whole wall to fill these?
they are only about 0.5-1cm, and one layer 'deep'...

will a new coat "grip" on otherwise smooth plaster that was put up a week before, or should we just use plaster to fill and smooth only the problem areas?

many thanks,

Nicholas

 

[stevethespreader]

thanks for the clarification Steve, much appreciated

if i can ask about minor imperfections and small pits in our finish (not cracks due to poor prep): can we apply another coat of plaster over the whole wall to fill these?
they are only about 0.5-1cm, and one layer 'deep'...

will a new coat "grip" on otherwise smooth plaster that was put up a week before, or should we just use plaster to fill and smooth only the problem areas?

many thanks,

Nicholas

if they are minor imperfections you can use joint cement i use wondertex http://www.wondertex.co.uk/drywall_finishing_systems.html you get a good finish its better than easifill just put on on over the blemishes and wait till dry and rub down "lightly" it would pay you to have a bag handy if you have more plastering to do you can get a 25k bag for a tenner down my way, if you cant get that then get gyproc joint cement or easifill or you can reskim but whats to say you are not going to have blemishes in the next coat? if you want to reskim just give it a coat of pva but im not to sure your first skim stuck to the wall that well, in anycase joint cement is a must for you as even pros leave the odd blemish that needs snagging i wouldent worry about minor imperfections like that as the joint cement will make them good