diy external plastering basics

[swimmydeepo]

I'm thinking of plastering an external concrete blocks wall of a terrace house....never done plastering before. I've done a bit of research and found some relevant points:

-Cement based plaster is recommended (not Gypsum)

-Use of PVA bonding on concrete (if porous)

-10kg of plaster will cover about 5 sq metres of 3mm thickness (is this calculation based on mixed plaster or dry?)

-Timber Grounds should be used at about 900mm from each other to keep level

-Alternatives ot Timber Grounds are PVC and Metal beads

-Scoring layers if more than one coat is applied

I'm sure there is more than this few points to be considered. Any suggestion appreciated.

[meow2222]

Sounds like youre overcomplicating a very simple thing. Its called rendering

NT

[John Rumm]

Rendering...

Plain ole sand and cement. Add a bit of sharp sand if you want more texture, or use silver or plastering sand if you want a fine finish (if this is your first attempt, I would probably not got for that!)

and if its something like thermal blocks or any other difficult to render base, then nail stainless steel expanded metal lath all over it first.

Depends on the thickness you want. Normally you use two coats - a thicker scratch coat and thinner finish coat. A square meter of finished render of 1" total thickness would need something like 50kg of sand and

7.5kg of OPC using a 6:1 mix.

IIUC, Renders don't want to be too strong - they should be parasitic and "give" with whatever base they are on, rather than being structures in their own right.

Metal beads are probably easiest to rule off against. Use corner beads and render stop beads for neat edges.

Yup, either scoring comb or just a block of wood with some small nail heads poking out.

Something like stipple is the easiest finish to get looking good if you are starting with no previous experience. Base coat on, and leave to go off a bit before scratching up. Let that dry for a few days, then do you finish coat - get it level ish, but don't worry too much about trowel marks. Again let it dry a little, and then smooth out the worst of the marks with the trowel. Then get a stiff brush (nylon broom head or similar) and firmly tamp the surface all over.

Oh, and try not to do it in a rain storm, it don't help the finish! (DAMHIK)

My first stab at it:

[meow2222]

If you want a dead straight square look, its a 2 coat job, aligning it all first.

If you want a more hand done look that suits older houses, it can be done and finished with 1 coat and no worry about alignment. For this, just

1. mix some plasticised mortar
2. trowel the mix on, wiping only upward or sideways (you'll soon see why),
3. then trowel it smoothish, but dont get fussy
4. dip a paintbrush in water and gently paint downward on the wet render. This smooths the surface and gets rid of trowel edge lines and the visible edges of slight hollows. Done.

NT

[Stuart Noble]

A dry sponge in a circular motion is the norm for 3) I think. It's knowing exactly when to do it that's difficult. Too soon or too late is no good.

[swimmydeepo]

Without reading this comments I would have used a stronger mix...thanks for your link, John. Render Stop Beads? Never heard of them before...I can see why they are useful though. Paintbrush of water or sponge? I'll have a try both ways.

Thanks for all your comments.