Painting outer wall - need some advice

Rollerball · 19 Jan 2011

I have a fairly rough and ready out-building that appears to be made of breeze-blocks and which seems to have a cement render.

Not sure when it was last painted, must have been at least 10 years ago. It's painted white. The outer paint layer is flaking off, sometimes in large chunks, only to reveal another layer of white underneath.

The north facing portion of it also has a thin film of green algae over most of it.

I need to scrape off the flaking paint of course, but how about the algae? How best to remove that?

Also, what type of paint should I use to re-paint it with? Are there any which are 'algae resistant'? I haven't painted anything for ages, hence the questions. I guess I'll need a roller too.

Thanks

TheDec · 19 Jan 2011

Firstly you will need to remove all loose and flaking paintwork, you can both kill off and remove the algae with a mild soloution of household bleach, (a cupfull to a gall of water) Use a stiff bristle brush for this, and wash down with clean water and allow to dry.

Sandtex would be a good choice of paint, should offer years of protection, you say there is a layer of white underneath your topcoat of paint. If this is chalky and leaves a white powdery residue on your hand post back for more advice prior to painting.

Dec.

Rollerball · 19 Jan 2011

Many thanks for the advice. I'll check if the other layer leaves a chalky residue - if it does, what does that indicate?

TheDec · 20 Jan 2011

All it means is the underlying paint is unstable and wiil need sealing before it is painted.

Dec

Rollerball · 20 Jan 2011

I see - what would I use to seal it if so?

TheDec · 20 Jan 2011

Either an oil based primer sealer or stabilising soloution.

Dec.

AbnerWright · 21 Jan 2011

I read somewhere that for new and powdery surface use 1 coat of Oil Based Sealer and for normal and sound surface apply 1 coat of Water Based Sealer. After using sealers accordingly, apply 2 coats of Algae Resistant Emulsion.

Rollerball · 21 Jan 2011

Thanks for the great advice.

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Painting outer wall - need some advice

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