Can anyone recommend the best way to smooth out badly-rendered, painted external walls, in a cost-effective way? Due to the fact that the wall has been painted, I'm not sure if simply applying a skim-coat of sand & cement is a viable option. perhaps there is some kind of additive that would make it viable and durable...

TIA

Al

On 13/10/16 18:42, Al wrote:
Can anyone recommend the best way to smooth out badly-rendered, painted external walls, in a cost-effective way? Due to the fact that the wall has been painted, I'm not sure if simply applying a skim-coat of sand & cement is a viable option. perhaps there is some kind of additive that would make it viable and durable...

TIA

Al


I am fairly sure this would work:

Soak wall in diluted (1:1) water-SBR (not PVA, SBR is more penetrative
and 100% water resistant).

Prepare a cement slurry with the same 1:1 SBR water mix to a thin honey
consistency and paint on 1m2 at a time immediately before applying render.

Test this first on perhaps an old paving slab or bit of ply just to make
sure the render doesn't slip off. That's the only risk I can think off.

The result will be as strong as the paint ultimately and will be
forgiving of a certain amount of friability.


There may be other ideas forthcoming...

Al wrote

Can anyone recommend the best way to smooth out badly-rendered,
painted external walls, in a cost-effective way? Due to the fact that the
wall has been painted, I'm not sure if simply applying a skim-coat of
sand & cement is a viable option.

perhaps there is some kind of additive that would make it viable and
durable...

Unlikely IMO.

On Thu, 13 Oct 2016 20:12:01 +0100, Tim Watts wrote:

Can anyone recommend the best way to smooth out badly-rendered,
painted
external walls,

One of our gable walls had been fully rendered over the old painted
stonework. One winter an area of render fell off, tapping the
remaining render started as "how much has blown?" but rapidly changed
to "is there any that isn't?" (There wasn't...). Failure was at the
paint layer.

Soak wall in diluted (1:1) water-SBR (not PVA, SBR is more penetrative
and 100% water resistant).

Prepare a cement slurry with the same 1:1 SBR water mix to a thin honey
consistency and paint on 1m2 at a time immediately before applying
render.

Well it might work but will the SBR soak into and bind reliably the
paint, paint that is presumably a masonary paint and pretty damn
waterproof?

Pressure washing the wall to remove any loose (and not so loose)
paint before the SBR and render treatment will improve it's chances
of lasting well. The other painted bare stone and rendered walls here
got a good pressure washing before being repainted, quite a number of
years ago, that paint is still sound.

--
Cheers
Dave.

On 14/10/2016 08:19, Dave Liquorice wrote:
On Thu, 13 Oct 2016 20:12:01 +0100, Tim Watts wrote:

Can anyone recommend the best way to smooth out badly-rendered,
painted
external walls,

One of our gable walls had been fully rendered over the old painted
stonework. One winter an area of render fell off, tapping the
remaining render started as "how much has blown?" but rapidly changed
to "is there any that isn't?" (There wasn't...). Failure was at the
paint layer.

Soak wall in diluted (1:1) water-SBR (not PVA, SBR is more penetrative
and 100% water resistant).

Prepare a cement slurry with the same 1:1 SBR water mix to a thin honey
consistency and paint on 1m2 at a time immediately before applying
render.

Well it might work but will the SBR soak into and bind reliably the
paint, paint that is presumably a masonary paint and pretty damn
waterproof?

Pressure washing the wall to remove any loose (and not so loose)
paint before the SBR and render treatment will improve it's chances
of lasting well. The other painted bare stone and rendered walls here
got a good pressure washing before being repainted, quite a number of
years ago, that paint is still sound.

or fix expanded metal lath over it all and re-render...


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
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On 14/10/16 09:39, John Rumm wrote:
On 14/10/2016 08:19, Dave Liquorice wrote:
On Thu, 13 Oct 2016 20:12:01 +0100, Tim Watts wrote:

Can anyone recommend the best way to smooth out badly-rendered,
painted
external walls,

One of our gable walls had been fully rendered over the old painted
stonework. One winter an area of render fell off, tapping the
remaining render started as "how much has blown?" but rapidly changed
to "is there any that isn't?" (There wasn't...). Failure was at the
paint layer.

Soak wall in diluted (1:1) water-SBR (not PVA, SBR is more penetrative
and 100% water resistant).

Prepare a cement slurry with the same 1:1 SBR water mix to a thin honey
consistency and paint on 1m2 at a time immediately before applying
render.

Well it might work but will the SBR soak into and bind reliably the
paint, paint that is presumably a masonary paint and pretty damn
waterproof?

Pressure washing the wall to remove any loose (and not so loose)
paint before the SBR and render treatment will improve it's chances
of lasting well. The other painted bare stone and rendered walls here
got a good pressure washing before being repainted, quite a number of
years ago, that paint is still sound.

or fix expanded metal lath over it all and re-render...


If you are going to do that, strip the blown stuff first.

And save te mesh.

--
To ban Christmas, simply give turkeys the vote.

On 14/10/16 09:39, John Rumm wrote:
On 14/10/2016 08:19, Dave Liquorice wrote:
On Thu, 13 Oct 2016 20:12:01 +0100, Tim Watts wrote:

Can anyone recommend the best way to smooth out badly-rendered,
painted
external walls,

One of our gable walls had been fully rendered over the old painted
stonework. One winter an area of render fell off, tapping the
remaining render started as "how much has blown?" but rapidly changed
to "is there any that isn't?" (There wasn't...). Failure was at the
paint layer.

Soak wall in diluted (1:1) water-SBR (not PVA, SBR is more penetrative
and 100% water resistant).

Prepare a cement slurry with the same 1:1 SBR water mix to a thin honey
consistency and paint on 1m2 at a time immediately before applying
render.

Well it might work but will the SBR soak into and bind reliably the
paint, paint that is presumably a masonary paint and pretty damn
waterproof?

Pressure washing the wall to remove any loose (and not so loose)
paint before the SBR and render treatment will improve it's chances
of lasting well. The other painted bare stone and rendered walls here
got a good pressure washing before being repainted, quite a number of
years ago, that paint is still sound.

or fix expanded metal lath over it all and re-render...



Add a layer of celotex at the same time

On Thursday, 13 October 2016 18:42:23 UTC+1, Al wrote:
Can anyone recommend the best way to smooth out badly-rendered, painted external walls, in a cost-effective way? Due to the fact that the wall has been painted, I'm not sure if simply applying a skim-coat of sand & cement is a viable option. perhaps there is some kind of additive that would make it viable and durable...

TIA

Al

Assuming you want it look as presently.
If the rendering is sound (ie firmly attached( the paint can be removed by sand blasting (Tool Hire Shop.)
If it's not sound, it will have to be chipped off.
Either hammer and chisel or a power chisel.
Quite often it comes away easily.

Applying anything on top of paint is likely to fail.

Thanks to everyone for the helpful suggestions. Both the rendering and the paint is very sound and well-attached. I may be wrong, but am I right in thinking that there are a lot of "we'll coat your house with our special coating; it will last till the end of time or your money back" ;-) companies, that seem to be able to apply their special coating and it generally seems to last very well? I wonder what materials and methods they use... Whatever they use, as sound surface on which to apply their coating is a prerequisite for durability anyway, right?

Al