Any ideas ?

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Fatarm

Trainee mod
What's caused this?was working in this estate doing some internal work..and seen this on most of the houses, the customer was telling me the NHBC? Are involved now
 

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t33ch

Active Member
Search tinternet. There's companies that make gear just for solving this.
Probably subsidiaries of the render companies!
 

flynnyman

Well-Known Member
Yep deffo Algee especially with all them over hanging trees lol they must be less than ten years old if NHBC are involved? I recon it might have something to do with the mortar used or the type of blocks, it looks like it's bleeding. Something's had a reaction with something, maybe the render and the wrong primmer used? Maybe the the dye in the mesh is bleeding through? Has it had cavity wall insulation fitted? Does the stain go all the way through the render or is it just on the surface?
 

t33ch

Active Member
... I recon it might have something to do with the mortar used or the type of blocks, it looks like it's bleeding. ...Does the stain go all the way through the render or is it just on the surface?

AFAIK...
The colour can depend on what's in the render that the algae feed on (e.g. cement has iron in it) but it's mainly a problem with the rough surface giving a huge surface area to grow on and sheltered parts that shade the algae from UV which would kill it.

Really damp conditions (e.g. Western, eastern northern, southern and central Ireland) will make things worse. Porous render will also make things worse so I'd expect it to happen less in silicone based renders.
Depth of growth will depend on material as cement renders are too alkaline to support deep penetration, but if a hairline crack appears, you are knackered as it will be like a algae holiday camp.
 

flynnyman

Well-Known Member
Unless this is common on every rendered house in the area, not just this site then it might be algee but I doubt it.
 

Fatarm

Trainee mod
Yep deffo Algee especially with all them over hanging trees lol they must be less than ten years old if NHBC are involved? I recon it might have something to do with the mortar used or the type of blocks, it looks like it's bleeding. Something's had a reaction with something, maybe the render and the wrong primmer used? Maybe the the dye in the mesh is bleeding through? Has it had cavity wall insulation fitted? Does the stain go all the way through the render or is it just on the surface?
Houses are only 9 years old....I've never seen the red staining before,looks like an paintball attack:eek:
 

Cornelius

Well-Known Member
All the houses on the new build slum down the road from me look like that, filthy and block work grinning through, it’s an eyesore.
 

Stevieo

Royal Spin Doctor
AFAIK...
The colour can depend on what's in the render that the algae feed on (e.g. cement has iron in it) but it's mainly a problem with the rough surface giving a huge surface area to grow on and sheltered parts that shade the algae from UV which would kill it.

Really damp conditions (e.g. Western, eastern northern, southern and central Ireland) will make things worse. Porous render will also make things worse so I'd expect it to happen less in silicone based renders.
Depth of growth will depend on material as cement renders are too alkaline to support deep penetration, but if a hairline crack appears, you are knackered as it will be like a algae holiday camp.

Ireland is jumping with it. Plenty people making a living cleaning it up.

I think you might be muddling up the iron thing though. Think algae is a thing all on its own.

You basically clean it with acid and paint of a sealant and that's you shut of it.

https://www.homeperfections.co.uk/single-post/2017/10/11/Dealing-with-red-staining-on-house-walls

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