I need to render some outside wall patches, some of which is painted
brickwork, then overpaint it all.
Is there a site with some tips on how to do bare brick and painted brick The
bare brick is extremely dry and like blotting paper - you can squirt a hose
at it and the water just disappears as it hits the wall - spooky to look at
!
(Unibond it first maybe?) or can someone here enlighten me please.

Questions I know about so far.... no doubt others I may not have thought
of...

1) What materials ( ordinary builders sand and Portland cement ?)
2) What mix ( 5 : 1 ? )
3) Any additives ( PVA or washing up liquid and how much ?)
4) How dry/sloppy a mix ( as dry as possible or wet as possible, or just
nice and workable?)
5) If Unibonding the painted bricks, do I apply a coat and let it dry and
another and wait to go tacky ?
6) After levelling, how long to wait until "polishing to the usual matt
finish", presumably with a wood float.

I have done some plastering but not rendering...

Thanks,

Nick

Hi Mick,

This may help, but I've never tried myself.

http://www.goldtrowel.org/rendering.asp

Cheers,
Mark

Nick wrote:
Questions I know about so far.... no doubt others I may not have thought
of...

1) What materials ( ordinary builders sand and Portland cement ?)
2) What mix ( 5 : 1 ? )

1:1:6 cement:lime:sharp sand (you can get special rendering sand, but
it's hard work).


3) Any additives ( PVA or washing up liquid and how much ?)

No. Certainly not washing up liquid for anything!


4) How dry/sloppy a mix ( as dry as possible or wet as possible, or just
nice and workable?)

A little drier than the mix for brick laying.


5) If Unibonding the painted bricks, do I apply a coat and let it dry and
another and wait to go tacky ?

No, don't. Just apply the PVA 1:5 PVA/water and render on it straight
away. Can't you get any of the paint off? It would be better.


6) After levelling, how long to wait until "polishing to the usual matt
finish", presumably with a wood float.

Use a wooden or plastic one, let the render go off until resilient
to the touch but not hard, then go at it with your float. Be careful
of adding too much water.

"Chris Bacon" wrote in message
...
Nick wrote:
Questions I know about so far.... no doubt others I may not have thought
of...

1) What materials ( ordinary builders sand and Portland cement ?)
2) What mix ( 5 : 1 ? )

1:1:6 cement:lime:sharp sand (you can get special rendering sand, but
it's hard work).


3) Any additives ( PVA or washing up liquid and how much ?)

No. Certainly not washing up liquid for anything!


4) How dry/sloppy a mix ( as dry as possible or wet as possible, or just
nice and workable?)

A little drier than the mix for brick laying.


5) If Unibonding the painted bricks, do I apply a coat and let it dry and
another and wait to go tacky ?

No, don't. Just apply the PVA 1:5 PVA/water and render on it straight
away. Can't you get any of the paint off? It would be better.


6) After levelling, how long to wait until "polishing to the usual matt
finish", presumably with a wood float.

Use a wooden or plastic one, let the render go off until resilient
to the touch but not hard, then go at it with your float. Be careful
of adding too much water.

Hi Chris,
Thanks for the tips - all noted
I was walking past a house the other day where there was rendering going on
( PVA /washing up liquid containers on the wall) and the carpenter there
said that the renderer was using it in his mix as a plasticizer he thought,
but didn't know for sure - hence the query.... and he was using ordinary
building sand - would this give a smoother finish to sharp sand ?
I have several bags of building sand left over so was hoping to be able to
use it if possible .....

Nick

Nick wrote:
I was walking past a house the other day where there was rendering going on
( PVA /washing up liquid containers on the wall) and the carpenter there
said that the renderer was using it in his mix as a plasticizer he thought,
but didn't know for sure - hence the query....

I would not employ this person (the one doing the rendering). The
"plasticising" effect of washing-up liquid is great, it makes the
muck go on nicely, however that's all it's useful for, and it can
be quite bad for the quality of the final result. A proper
plasticiser is far, far better, but it's still really only helping
with the handling of the stuff when you put it on - the final
set render *may* be harder when using plasticiser, though. With
render, you don't really want an extra-hard finish, hard enough
is all you want. If it's very hard, then the render won't cope at
all well with any movement, and may crack off in slabs. That's why
1:1:6 is nice, the lime makes it handle very nicely, and the set is
not vert hard (although it is quite hard enough!).


and he was using ordinary
building sand - would this give a smoother finish to sharp sand ?

Yes, perhaps - however, it contains a lot of "fines", and is
very likely to shrink and crack when it sets. The special sand
I mentioned for rendering has a very even grain size indeed,
it looks like caster sugar but sandy coloured. It's hard to work,
but gives a very superior result. Washed sharp sand is probably
the way to go.


I have several bags of building sand left over so was hoping to be able to
use it if possible .....

Use it for something else, or give it away - don't put it on
your walls!

Re. PVA - put it on and render straight over, because if it sets,
you may have trouble getting the mortar to stay on the wall - the
PVA is supposed to leach into the brickwork *and into the render
you put on* - giving a strong bond when set.

"Chris Bacon" wrote in message
...
Nick wrote:
I was walking past a house the other day where there was rendering going
on ( PVA /washing up liquid containers on the wall) and the carpenter
there said that the renderer was using it in his mix as a plasticizer he
thought, but didn't know for sure - hence the query....

I would not employ this person (the one doing the rendering). The
"plasticising" effect of washing-up liquid is great, it makes the
muck go on nicely, however that's all it's useful for, and it can
be quite bad for the quality of the final result. A proper
plasticiser is far, far better, but it's still really only helping
with the handling of the stuff when you put it on - the final
set render *may* be harder when using plasticiser, though. With
render, you don't really want an extra-hard finish, hard enough
is all you want. If it's very hard, then the render won't cope at
all well with any movement, and may crack off in slabs. That's why
1:1:6 is nice, the lime makes it handle very nicely, and the set is
not vert hard (although it is quite hard enough!).


and he was using ordinary building sand - would this give a smoother
finish to sharp sand ?

Yes, perhaps - however, it contains a lot of "fines", and is
very likely to shrink and crack when it sets. The special sand
I mentioned for rendering has a very even grain size indeed,
it looks like caster sugar but sandy coloured. It's hard to work,
but gives a very superior result. Washed sharp sand is probably
the way to go.


I have several bags of building sand left over so was hoping to be able
to use it if possible .....

Use it for something else, or give it away - don't put it on
your walls!

Re. PVA - put it on and render straight over, because if it sets,
you may have trouble getting the mortar to stay on the wall - the
PVA is supposed to leach into the brickwork *and into the render
you put on* - giving a strong bond when set.




Hi Chris

Thanks for the rapid and informative reply - I now understand the reasoning
!

I will try and do the job over the next week weather permitting.

Thanks again,

Nick

In article ,
says...
snip
No, don't. Just apply the PVA 1:5 PVA/water and render on it straight
away. Can't you get any of the paint off? It would be better.

I'd have thought a wire brush in an angle grinder would make a fairly
easy job of that.

"Rob Morley" wrote in message
t...
In article ,
says...
snip
No, don't. Just apply the PVA 1:5 PVA/water and render on it straight
away. Can't you get any of the paint off? It would be better.

I'd have thought a wire brush in an angle grinder would make a fairly
easy job of that.

Hi Rob,

Thanks for the reply - I have those so will give that a go first.....

I suppose I could always fix some suitable mesh on the wall first
to give it a good key...

Nick

In article , says...

"Rob Morley" wrote in message
t...
In article ,
says...
snip
No, don't. Just apply the PVA 1:5 PVA/water and render on it straight
away. Can't you get any of the paint off? It would be better.

I'd have thought a wire brush in an angle grinder would make a fairly
easy job of that.

Hi Rob,

Thanks for the reply - I have those so will give that a go first.....

I suppose I could always fix some suitable mesh on the wall first
to give it a good key...

EML - expanded metal lath

Nick wrote:
"Rob Morley" wrote in message
t...
In article ,
says...
snip
No, don't. Just apply the PVA 1:5 PVA/water and render on it straight
away. Can't you get any of the paint off? It would be better.

I'd have thought a wire brush in an angle grinder would make a fairly
easy job of that.

Hi Rob,

Thanks for the reply - I have those so will give that a go first.....

I suppose I could always fix some suitable mesh on the wall first
to give it a good key...

Nick

We dont know what kind of bricks youve got, nor what type of building.
With some buildings rendering in sand/cement is really not a smart
idea. Lime render is safe on any building type.


Wirebrushing bricks may do significant damage to the bricks, depending
on what type they are. Cement rendering may do likewise, again
depending. Use lime.

If you use EML, the common galv EML is not so good, as it rusts and
makes a right mess of it all. This doesnt happen with SS, though its
several times the price.


NT

wrote in message
oups.com...
Nick wrote:
"Rob Morley" wrote in message
t...
In article ,
says...
snip
No, don't. Just apply the PVA 1:5 PVA/water and render on it straight
away. Can't you get any of the paint off? It would be better.

I'd have thought a wire brush in an angle grinder would make a fairly
easy job of that.

Hi Rob,

Thanks for the reply - I have those so will give that a go first.....

I suppose I could always fix some suitable mesh on the wall first
to give it a good key...

Nick

We dont know what kind of bricks youve got, nor what type of building.
With some buildings rendering in sand/cement is really not a smart
idea. Lime render is safe on any building type.


Wirebrushing bricks may do significant damage to the bricks, depending
on what type they are. Cement rendering may do likewise, again
depending. Use lime.

If you use EML, the common galv EML is not so good, as it rusts and
makes a right mess of it all. This doesnt happen with SS, though its
several times the price.


NT

Hi,
Thanks for the added info - the bricks are in very poor shape approx 110
years old and pretty weathered - I would guess that in their day they were
the cheapest you could get, or even rejects..... Part of the wall is already
rendered and there was once an outside toilet, which was removed, exposing
the area needing to be rendered.

By "damage to the bricks" do you mean cosmetic damage or something else ?
Why would it matter if its going to be rendered over ?

In any case, I will take the advice and use Lime in the render

Thanks again,
Nick

Nick wrote:
wrote in message

We dont know what kind of bricks youve got, nor what type of building.
With some buildings rendering in sand/cement is really not a smart
idea. Lime render is safe on any building type.


Wirebrushing bricks may do significant damage to the bricks, depending
on what type they are. Cement rendering may do likewise, again
depending. Use lime.

If you use EML, the common galv EML is not so good, as it rusts and
makes a right mess of it all. This doesnt happen with SS, though its
several times the price.


NT

Hi,
Thanks for the added info - the bricks are in very poor shape approx 110
years old

ok then you do need to use lime not cement


and pretty weathered - I would guess that in their day they were
the cheapest you could get, or even rejects..... Part of the wall is already
rendered and there was once an outside toilet, which was removed, exposing
the area needing to be rendered.

By "damage to the bricks" do you mean cosmetic damage or something else ?

cosmetic and structural: damaged soft bricks soak up water, freeze, and
slowly disintegrate. Eventually the only solution is to rebuild the
wall.


Why would it matter if its going to be rendered over ?

because its the bricks that hold the wall up, that are teh wall. You
dont want them disintegrating and the wall becoming unstable. Its a
very slow process, but thats what cement does to soft bricks.


In any case, I will take the advice and use Lime in the render

The advice was not to use lime in the render, but to use lime render.
Lime render does not contain cement. Cement based renders have the
following problems on Victorian properties:
- they trap water thus cause brick damage
- they adhere to the brick more strongly tha the brick adheres to
itself, thus they often damage the brick when they eventually come off
- being impervious they prevent the wall drying out, and increase the
chances of damp in the house

Lime render is 3:1 by volume of sand and lime putty. Lime putty is
simple to make yourself. It is very slow setting, it takes weeks, and
if frost is likely where you are it should be covered over until set.


The bricks were probably fine until someone cement rendered them.
Typically bricks were made onsite, with the junk used on the inner
leaf.

An angle grinder and wirebrush would do substantial damage to Victorian
soft bricks, and would be truly unwise.

If you want more detail on Victorian properties and cement and lime,
http://www.periodproperty.co.uk/cgi-...ing/forum2.pl?


NT

wrote in message
ups.com...
Nick wrote:
wrote in message

We dont know what kind of bricks youve got, nor what type of building.
With some buildings rendering in sand/cement is really not a smart
idea. Lime render is safe on any building type.


Wirebrushing bricks may do significant damage to the bricks, depending
on what type they are. Cement rendering may do likewise, again
depending. Use lime.

If you use EML, the common galv EML is not so good, as it rusts and
makes a right mess of it all. This doesnt happen with SS, though its
several times the price.


NT

Hi,
Thanks for the added info - the bricks are in very poor shape approx 110
years old

ok then you do need to use lime not cement - OK noted ...


and pretty weathered - I would guess that in their day they were
the cheapest you could get, or even rejects..... Part of the wall is
already
rendered and there was once an outside toilet, which was removed,
exposing
the area needing to be rendered.

By "damage to the bricks" do you mean cosmetic damage or something else ?

cosmetic and structural: damaged soft bricks soak up water, freeze, and
slowly disintegrate. Eventually the only solution is to rebuild the
wall.


Why would it matter if its going to be rendered over ?

because its the bricks that hold the wall up, that are teh wall. You
dont want them disintegrating and the wall becoming unstable. Its a
very slow process, but thats what cement does to soft bricks.


In any case, I will take the advice and use Lime in the render

The advice was not to use lime in the render, but to use lime render.
Lime render does not contain cement. Cement based renders have the
following problems on Victorian properties:
- they trap water thus cause brick damage
- they adhere to the brick more strongly tha the brick adheres to
itself, thus they often damage the brick when they eventually come off
- being impervious they prevent the wall drying out, and increase the
chances of damp in the house

Lime render is 3:1 by volume of sand and lime putty. Lime putty is
simple to make yourself. It is very slow setting, it takes weeks, and
if frost is likely where you are it should be covered over until set.


The bricks were probably fine until someone cement rendered them.
Typically bricks were made onsite, with the junk used on the inner
leaf.

An angle grinder and wirebrush would do substantial damage to Victorian
soft bricks, and would be truly unwise.

If you want more detail on Victorian properties and cement and lime,
http://www.periodproperty.co.uk/cgi-...ing/forum2.pl?


NT


I reckon this is exactly what I have got - fortunately its on a sheltered
wall that rarely if ever gets / got wet and it can breathe from the
inside. - I will be careful in getting a key on the bricks and not lay into
it with anything brutally mechanical... the shame / concern is that the wall
is already 80% rendered with what almost certainly is a cement render
unless it looks identical to lime render...

It sounds like a discussion with Anna Kettle may also be worthwhile for some
additional hints and tips...
especially with how to make lime putty, which I hadn't even heard of...

Thanks again,
Nick

Nick wrote:
[ snip lime and stuff ]
I reckon this is exactly what I have got - fortunately its on a sheltered
wall that rarely if ever gets / got wet and it can breathe from the
inside. - I will be careful in getting a key on the bricks and not lay into
it with anything brutally mechanical... the shame / concern is that the wall
is already 80% rendered with what almost certainly is a cement render
unless it looks identical to lime render...

It doesn't. Lime render is soft. Cement render is very hard. To match
what you've got, and avoid problems due to widely dissimilar renderings,
use 1:1:6, which is widely accepted.

meow222 wrote:
Typically bricks were made onsite

In Victorian times? I disagree with that. What makes you
think it's so?

Nick wrote:

I reckon this is exactly what I have got - fortunately its on a sheltered
wall that rarely if ever gets / got wet and it can breathe from the
inside. - I will be careful in getting a key on the bricks and not lay into
it with anything brutally mechanical... the shame / concern is that the wall
is already 80% rendered with what almost certainly is a cement render
unless it looks identical to lime render...

The 2 are significantly different. Lime render is essentially chalk,
and ages by gradually wearing down, thus has a self cleaning action. It
is also self repairing, it reacts with CO2 to grow hard crystals across
any cracks, thus can tolerate movement and repair itself.

Use round corners with lime rather than square, as its not as hard as
cement.


It sounds like a discussion with Anna Kettle may also be worthwhile for some
additional hints and tips...
especially with how to make lime putty, which I hadn't even heard of...

Thanks again,
Nick

Either buy it, or else get a bag of hydrated lime from a BM, dump it in
a bin, mix with water to form a paste, and store it either with an
airtight lid, or under a layer of water, for a few weeks. Its then
ready to go.

3:1 is the usual mix. Dont add any cement.

Lime rendering is easier than cement. It has lots of body, sticks
better, and youve got all the time you want to get the surface right.
Have fun.


NT

Chris Bacon wrote:
meow222 wrote:

Typically bricks were made onsite

In Victorian times? I disagree with that. What makes you
think it's so?

I guess it all depends on when and where. If its late Victorian in
London, they wont be on site bricks, if its early Victorian in the
country, they will be. Even in London, bricks were made on site for a
long time.

If theyre the later wire cut type, sure to be off site, but even at the
end of Vic period, hand made stocks were standard.


NT