Can anyone recommend the best way to smooth out badly-rendered, painted ext ernal walls, in a cost-effective way? Due to the fact that the wall has bee n 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...
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.
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.
Add a layer of celotex at the same time :)
xternal walls, in a cost-effective way? Due to the fact that the wall has b een painted, I'm not sure if simply applying a skim-coat of sand & cement i s a viable option. perhaps there is some kind of additive that would make i t viable and durable...
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 th inking that there are a lot of "we'll coat your house with our special coat ing; it will last till the end of time or your money back" ;-) companies, t hat seem to be able to apply their special coating and it generally seems t o 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 prerequisit e for durability anyway, right?
Al
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