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.

wrote:
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.


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


NT

wrote:

I'm thinking of plastering an external concrete blocks wall of a
terrace house....never done plastering before.

Rendering...

I've done a bit of research and found some relevant points:
-Cement based plaster is recommended (not Gypsum)

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!)

-Use of PVA bonding on concrete (if porous)

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.

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

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.

-Timber Grounds should be used at about 900mm from each other to keep
level
-Alternatives ot Timber Grounds are PVC and Metal beads

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

-Scoring layers if more than one coat is applied

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

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

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:

http://www.internode.co.uk/loft/rendering.htm

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
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| John Rumm - john(at)internode(dot)co(dot)uk |
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wrote:
wrote:
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.


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


NT


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
0. mix some plasticised mortar
1. trowel the mix on, wiping only upward or sideways (you'll soon see
why),
2. then trowel it smoothish, but dont get fussy
3. 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

wrote:
wrote:
wrote:
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.

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


NT


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
0. mix some plasticised mortar
1. trowel the mix on, wiping only upward or sideways (you'll soon see
why),
2. then trowel it smoothish, but dont get fussy
3. 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

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.

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.