preparation of exterior wall before painting

8 May 2011
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United Kingdom

I'm planning to repaint our 1920s/30s terraced house. there is a rough render on the front, last painted approx 10yrs ago

there are cracks in the render approx 1-2mm wide. what is the best filler for these? it looks like a mortar based repair has been performed on some areas in the past.

in several areas there are very thick layers of paint which have cracked (2-3mm wide) and the render underneath has reduced almost to powder. I don't think taking this paint off is an option. what is best applied to the paint cracks to fill/seal them before painting?

many thanks
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Hi stickmonster, like the name! :)

Filling narrow cracks in rough render is tricky and often leaves obvious signs of repair. I like to use a cement based powder filler (something like polycell weatherproof filler) which can be mixed a little on the wet side. This will allow you to force the filler well into the cracks with the aid of an old paintbrush and blend the repair in nicely. This type of product should be primed with an alkali resistant primer, so you may prefer to use a regular exterior filler, which will usually work fine.

Where the paint is cracked/powdery, you should remove all loose material with a stiff brush, before repairing and sealing the patches with a stabilising solution.

Once the repairs have all dried out, you can then begin your painting. Start by applying a slightly watered down coat over the repairs, before using the paint neat over the whole area to complete the job. ;)

You say that the underlying render if only in part has become powdery, you also say that these areas are covered in thick layers of paint which of cracked.

Therefore I am going to advise you not to undertake a re-paint until you have that render checked out, it seems to me that it has given up the ghost and any form of advice regarding a re-paint would only be a cosmetic solution that will never last.

Blown render will usually last for decades if you keep it covered with paint. A re-render will cost thousands.
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I don't disagree with that, yet the op has stated that the cracked and thickly applied paintwork is not going to be removed. Therefore to apply any paint system would'nt last another Winter, If the op decides only on a repaint surely it would be a better option to remove as much paint as he can and stabilise the powdery render. At least this way his newly applied paintwork will stand a far better chance of protecting the failing render.


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