Painting external render

roofmog · 8 Sep 2009

I am currently repainting the exterior of my 1820 end of terrace cottage. At some point in the past the exterior was rendered and the front painted white but the side gable end was not painted. I am now looking to paint this render as it now looks very dull and scruffy. I am planning to use a breathable coating - probably Sandtex ultra smooth masonry paint. Tests on a small area suggest I will need to use two coats owing to the blackness of the chips in the render. I am also considering using a stabilising primer first, but am a bit concerned that this may effect the breathability of the wall.

I am also having a bit of difficulty in identifying exactly what the wall was rendered with. It has a slightly yellow colour and is slightly dusty if you scratch it. It also has a patchy grey material growing on it which may be some kind of lichen. This can be removed with a stiff brush but it owing to the texture of the wall would probably take several days to remove. Any ideas as to what this material actually is and how to remove it. ( It does not appear on the already painted surface at the front)

Hopefully the attached pictture may help
View media item 14357

spread9264 · 14 Sep 2009

roofmog said:
I am currently repainting the exterior of my 1820 end of terrace cottage. At some point in the past the exterior was rendered and the front painted white but the side gable end was not painted. I am now looking to paint this render as it now looks very dull and scruffy. I am planning to use a breathable coating - probably Sandtex ultra smooth masonry paint. Tests on a small area suggest I will need to use two coats owing to the blackness of the chips in the render. I am also considering using a stabilising primer first, but am a bit concerned that this may effect the breathability of the wall.

I am also having a bit of difficulty in identifying exactly what the wall was rendered with. It has a slightly yellow colour and is slightly dusty if you scratch it. It also has a patchy grey material growing on it which may be some kind of lichen. This can be removed with a stiff brush but it owing to the texture of the wall would probably take several days to remove. Any ideas as to what this material actually is and how to remove it. ( It does not appear on the already painted surface at the front)

Hopefully the attached pictture may help
View media item 14357

spread9264 · 14 Sep 2009

this looks like it has been rendered with black spar/sand and cement.it looks like like you have a lot of algae too.try to brush this with a stiff brush or fine wire brush.or use a fungicide and a pressure washer to remove.i cannot tell you about the breathabily because this depends on the construction of your house.but if this worrys you can water down the first coat as masonry paint is water based by 60%paint40%water.it will probably take two more coats to cover. from simon the builder

roofmog · 16 Sep 2009

Thanks for the reply. I managed to scrub about 90-95% of the algae off with a stiff brush (took about 2 days). However a fungicidal wash has made no difference to the remaining bits. As it will be impossible to get rid of all of it will it cause any problems if I paint over the remainder.

spread9264 · 16 Sep 2009

personally any areas that are a bit suspect.i would paint with stabaliser to be on the safe side,just to stop any algea showing through.hope this has been helpfull. simon the builder

joe-90 · 16 Sep 2009

That doesn't look too bad to me. I think you'd get away with using a watered down masonry paint ( like a mist coat on new plaster) then a couple of coats of normal masonry paint. Look for one that is mould resistant, it is always a risk adding stuff to paint that might not be suited.

roofmog · 23 Sep 2009

A power washer did the trick. Took about nine hours in total to clear the wall completely, and at 10 litres a minute I'm very glad I don't have a water meter. I was a little concerned about how easily the washer removed the test patches of Sandtex masonry paint. However these had been applied direct to the surface without any cleaning or priming. I'm now waiting for the wall to dry out a bit berfore painting.

Thanks for all the suggestions. Attached is an "after" shot of the wall. I noticed that nearby trees also suffer from the same algae/lichen problem

View media item 15102

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Painting external render

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