Calling all plasterers...tips pls

fatchance

Hi all,

I'm hoping to do a small area inside my shed myself (4m sq), so can anyone please tell me the correct ratio/mix for plaster on a block wall?

I have seen it done before by professionals and once it is on the wall and levelled they come back to it ages later and do a circular motion on the dried/ nearly dried plaster...why is this done?

Can't seem to get the ratio right, plaster is not "sticking" to the wall. Other than sand/cement and water, do I need anything else in the mix?

Thanks all, really would love to tackle this little job myself.

10-10-20

I'm no plasterer, but the reason for the final run-over with the float is to finish-off/smooth the surface.

Are you wetting the wall before-hand? If not, it won't stick and will dry out instead of curing.
The ratio is as per on the bag, 3:1 or about that. The mix should not slump when troweled.

fatchance

3:1 is what I thought too, and I did wet the wall before hand. Maybe I'm not adding enough water - or too much?

For some reason I thought I was missing an ingredient (like skill!) such as mortisiser?

Thanks for the reply, more please.

The Hill Billy

Generally you would render an internal wall in 3 stages:
Scud coat (sand/cement 2:1)
Scratch coat (sand/cement 3:1 or bonding)
Skim coat (sand/cement 3:1 or plaster finish)

It sounds like you're leaving out the scud coat stage. This is needed allow the scratch coat stick to the wall.

To scud the wall:
1. Wet the wall to remove any dust (use a water/PVA mix).
2. Make a fairly "runny" 2:1 mix & "dash" it at the wall using a small trowel.
3. When the scud has set repeat step 1 & then you're good to go with your scratch coat.

d2ww

Hill Billy wrote:

Generally you would render an internal wall in 3 stages:
Scud coat (sand/cement 2:1)
Scratch coat (sand/cement 3:1 or bonding)
Skim coat (sand/cement 3:1 or plaster finish)

It sounds like you're leaving out the scud coat stage. This is needed allow the scratch coat stick to the wall.

To scud the wall:
1. Wet the wall to remove any dust (use a water/PVA mix).
2. Make a fairly "runny" 2:1 mix & "dash" it at the wall using a small trowel.
3. When the scud has set repeat step 1 & then you're good to go with your scratch coat.

Hi All,
Just removed a partition stud wall to knock two rooms into one, and am left with two vertical 110mm gaps with the underlying exposed blockwork, either side of the new room. The two rooms are block/plaster finish. I have cut two long strips of 9mm plasterboard to fill these gaps, but my problem is that the underlying blockwork is really uneven, the depth goes from 18mm up to 28mm and all points in between!!!
Does anyone have any suggestions as to how I can fill these two gaps?
Hill Billy above mentions "scud/scratch/skim" Is this the way to go and forget the P/board?
Btw, Does anyone know the ratio of thickness' (sic) of each layer of scud/scratch/skim.
Thanks
d2ww

jdpl28

Buy yourself a bag of bonding compound from a builders suppliers, and mix it up with a plaster mixer on a drill. Use this to bond your plasterboard to the wall. It can be dabbed in lumps to compencate for the unevenness of the wall.

d2ww

Thanks for that, Jdpl28, will head down to Chadwicks tomorrow.

GreeBo

are there studs either side of the gaps?
If so I would screw some batons to "extend" the studs and then just screw your plasterboard to this...

GreeBo

or, since
a) its a block wall
and
b) the gap is narrow
I would glue/screw some timber to the wall leaving it about 1cm shy of the existing plasterwork.
It doesnt need to be even or pretty, you are just filling the gap.
Then you can just plaster and skim over it.

It shouldnt be too hard to get a good finish as your float/trowel should span the gap.

d2ww

Oops, sorry Greebo, just saw your post. As I already had the plasterboard strips cut, I bonded these to the wall.
d2ww