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Red streaks on exterior walls - Bleeding

Posted by Exploring - Created: 4 years ago
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5 replies (Showing replies: 1 to 5)

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Posted by SallyDixon - 4 years ago

We washed the stains off really easily with a standard pressure washer [ladder] and some solution that is bought cheaply from any brico. Just ask for chelque chose pour les taches roses. It does not look as if it has worked fully at first but gets better over time.

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Posted by AQ-417490 - 4 years ago

This is a well known problem in Brittany. It might look unsightly, but is harmless. It is caused by the fact that the local sand used in the render has a naturally high level of iron oxide which leeches out on repeated exposure to rain, hence it is mostly south or west facing walls that are affected. Best cure is to apply a diluted bleach solution to the affected areas during a dry spell, which will remove the red stain, but might leave the wall looking blotchy and the staining will return again after further wet weather, particularly driving rain. So once the bleach solution has removed the stain, it is best to paint the entire wall / walls with any UK sourced masonry paint of about the same colour as the original wall (or different if you really want to change the entire wall colour). These paints are usually guaranteed for about 15 years, so should be good for at least 5 years and perhaps up to 10, if well applied with 2 coats.

You might have noticed that many houses in Brittany have these rain exposed walls clad with slates, either black or painted with masonry paint to match the colour of the other walls. Being waterproof, the  covered wall is completely protected. Simpler, however,to treat and paint.

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Posted by Alpacas - 4 years ago

I bet you have a slate roof.  These stains eminate from that but I would suggest that it would be easier and even cheaper to repaint the areas effected.

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Posted by Tryval - 4 years ago

It is a fungus, a neighbour had it treated last year with a clear liquid which it supposed to reactivate each time it gets wet, it wasn't cheap!

Kind Regards.

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Posted by Annabelle's Papa - 4 years ago

I always thought it was the metallic elements in the sand in the render/paint that oxidises with the air that turns to red streaks over time.

There are clear stabilising solutions you can buy and spray/brush on and I regret to say it but Dulux Weathershield is the best to paint over it, in the textured finish the sand is screened well to remove all metallic traces.

They said mushrooms..... that's a new one on me.