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Will a coat of exterior wall pain cover these wall stains?

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  • 11-07-2020 4:04pm
    #1
    3rdDegree
    Registered Users Posts: 1,261 ✭✭✭


    I have these dirty, red coloured streaks on one wall only of the side of the house. I was thinking of buying some standard exterior wall paint and painting over, but then it occurred to me that the stains might just come up through the new paint.

    Is it possible to tell just by looking at the pictures what those marks are and if a coat of paint will permanently cover them? Or would I have to pre-treat them with something before painting?

    Many thanks.


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    #2
    dok_golf
    Registered Users Posts: 1,090 ✭✭✭dok_golf


    That a fungus mate. Hit it with both a fungicidal wash and them hypochorite to bleach the staining


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    #3
    Dempo1
    Registered Users Posts: 26,933 ✭✭✭✭Dempo1


    3rdDegree wrote: »
    I have these dirty, red coloured streaks on one wall only of the side of the house. I was thinking of buying some standard exterior wall paint and painting over, but then it occurred to me that the stains might just come up through the new paint.

    Is it possible to tell just by looking at the pictures what those marks are and if a coat of paint will permanently cover them? Or would I have to pre-treat them with something before painting?

    Many thanks.

    Not sure that's fungus, I've seen this on reasonablly new houses, a chemical reaction with render that have not been painted, gable ends mainly. You'll need to give it a really good power wash, possibly bleach based. As it looks like a first painting, be prepared for at least two coats. Exterior masonry paints are acrylic based and should cover well. I've a 200 year old cottage with plaster render and use white, I'm guessing you'll a color which will help. Use a branded paint also, I know more expensive but worth it. Any decent paint retailer will offer advice but preparation crucial before painting.

    Is maith an scáthán súil charad.




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    #4
    [Deleted User]
    Posts: 14,344 ✭✭✭✭ [Deleted User]


    I'm not too clued into this, but from looking at your picture, it could be something that I see a fair bit.

    I think it's something to do with calcium inside the stone coming out. Something like that. I think it depends where the stone is sourced, but I see it a lot on houses in Cavan/Monaghan/Leitrim area. Often red patches of it. I have seen it washed off before. Bleach in a 'foam' bottle attached to a pressure washer to coat it and kill it off, and then washed with the pressure washer (but you need to take your time and use a relatively low pressure as you'll blow the pebble-dashing off if you use too high a pressure).


    A quick google search brings me to this website, if you scroll down, they clean it off and mention it's a common thing.

    https://roomwithaview.ie/gallery/


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    #5
    Dempo1
    Registered Users Posts: 26,933 ✭✭✭✭Dempo1


    [Deleted User] wrote: »
    I'm not too clued into this, but from looking at your picture, it could be something that I see a fair bit.

    I think it's something to do with calcium inside the stone coming out. Something like that. I think it depends where the stone is sourced, but I see it a lot on houses in Cavan/Monaghan/Leitrim area. Often red patches of it. I have seen it washed off before. Bleach in a 'foam' bottle attached to a pressure washer to coat it and kill it off, and then washed with the pressure washer (but you need to take your time and use a relatively low pressure as you'll blow the pebble-dashing off if you use too high a pressure).


    A quick google search brings me to this website, if you scroll down, they clean it off and mention it's a common thing.

    https://roomwithaview.ie/gallery/

    Yes, that's it, I knew it was some sort of chemical reaction. OP I didn't notice you've pepple dash so apologies, I don't think painting over pepple dash wise and yes, low pressure wash

    Is maith an scáthán súil charad.




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    #6
    whizbang
    Registered Users Posts: 1,924 ✭✭✭whizbang


    Its almost definitley Red Algae; grows where there is just enough porosity to hold it.

    Iron ore can cause a similar effect, but generally the material for renders doesnt carry it.


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    #7
    dok_golf
    Registered Users Posts: 1,090 ✭✭✭dok_golf


    Dempo1 wrote: »
    Not sure that's fungus, I've seen this on reasonablly new houses, a chemical reaction with render that have not been painted, gable ends mainly. You'll need to give it a really good power wash, possibly bleach based. As it looks like a first painting, be prepared for at least two coats. Exterior masonry paints are acrylic based and should cover well. I've a 200 year old cottage with plaster render and use white, I'm guessing you'll a color which will help. Use a branded paint also, I know more expensive but worth it. Any decent paint retailer will offer advice but preparation crucial before painting.

    Its fungus. I've been dealing with this for 25 years. Power washing without hitting it first with a fungicide will make it worse. The reason you see it on umpainted walls is that exterior paint has a fungicide in it already.


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