Yellow stains on newly painted pebbledash

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iona
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Joined: Tue Dec 20, 2016 2:04 pm

Yellow stains on newly painted pebbledash

Post by iona » Tue Dec 20, 2016 2:29 pm

Hello, our pebbledash exterior was painted white 3 months ago. It was pressure washed, then coated with (watered down I think) PVA, then 3 coats of Sandtex brilliant white. It had never been painted before and still had what I think was probably the original 1930s pebbledash on it.

I've just noticed that faint patches of yellow are starting to appear on the (concrete?) strip that runs around the base of the house and on some areas of the pebbledash. But I can't see any yet on the strip of bricks that is between the pebbledash and the concrete.

One area of pebbledash that is yellowing is an area that may be slightly damp, but I don't think the other yellow stains are in damp areas. And it is actually most noticeable under the porch where no rain would get to it.

Can anyone advise on what is causing this and what we can do about it? 2 pics attached (sideways - sorry!).

Thank you!

Iona
front.JPG
front.JPG (161.77 KiB) Viewed 2078 times
under porch roof.JPG
under porch roof.JPG (167.94 KiB) Viewed 2078 times

chloepoly
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Re: Yellow stains on newly painted pebbledash

Post by chloepoly » Wed May 31, 2017 11:30 am

Bumping this post - similar situation
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Colin
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Re: Yellow stains on newly painted pebbledash

Post by Colin » Wed May 31, 2017 8:55 pm

PVA, although cheap, would not be my choice for a primer, it can fail.
I would think the stain comes from minerals in the original render.
Because it wasn't supposed to be painted, stone and sand containing iron may have been used, and this is now showing up in the white paint.
If it's only a couple of area's, it may be worth trying a stain blocking primer on the patches and then painting over them, If it's lots of area's, try repainting the house using a Pliolite-based (oil-based) masonry paint, as a lot of these stains don't go through oil-based paints so easily. But do an experiment first

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