Stains coming through painted render, see pics - what is it?

Copperface · 24 Jul 2010

Hi,
Have attached two pics for reference.
As you can see I have some type of brown stains coming through the masonry paint which was applied to a new render. The render was a completely new application about three years ago and all the old was hacked off.
However, as per the pics, there is some type of brown stain coming through the exterior masonry paint, primarily on the north facing wall.
Can anyone tell me what it is and how to get rid of it? Can i seal the spots with something (like a knotting solution for masonry)?
My painter said that it was some type of impurity in the render coming through, but I have repainted a couple of spots and eventually it has come though again.
Any ideas/advice gratefully received.

sparkwright · 24 Jul 2010

Could it be rust from some old wall ties or some old nails?

Copperface · 24 Jul 2010

sparkwright said:
Could it be rust from some old wall ties or some old nails?

thanks for reply.....

No......in other places it is nowhere near where any wall ties or nails would be.

Closer inspection of some small areas where it is beginning shows that it appears to be some type of impurity that is coming out of the render.
I'm looking to seal the spots and paint over them but don't know what to use to do it.

paulc7617 · 24 Jul 2010

only a diy'er but maybe couple of coats of zinseer bin or even oil based undercoat, then over paint with your masonary paint. However i am sure the pros will be on later and give you sound advice.

Copperface · 24 Jul 2010

Hmmm, had never heard of Zinsser BIN before - looks good stuff.

B&Q have the areosol version for spot exterior use so will go and get some tomorrow and see if it works.

Many thanks.

Still not sure what's causing it though, but pretty sure it's something in the render that was put on - don't know if any experts know if this is a common thing?

Cheers

roughcaster · 24 Jul 2010

I think it could be iron pyrites in the actual roughcast/wet dash itself??? Small metal particles that rust over the years. I've seen it happen before. I don't think water based sealers/paints, wont stop it coming through again.

Copperface · 24 Jul 2010

yup, thought as much. Think I'll seal with Zinsser and chase around spot repainting as necessary.

Thanks.

jondecs · 24 Jul 2010

roughcaster said:
I think it could be iron pyrites in the actual roughcast/wet dash itself??? Small metal particles that rust over the years. I've seen it happen before. I don't think water based sealers/paints, wont stop it coming through again.

Interesting thoughts on the iron pyrates r/c. My thoughts before reading that it was 'new render', was that someone had used a wire brush to clean off before painting, leaving wire bristles trapped in the dash. I did a job earlier this year with same rusty stain spots. I dabbed some rust eater type stuff from halfords which sends rust black etc, then dabbed on zinsser 123 befor masonry paint. perfect 2 mths later.. but in past have used rust converter stuff then just white solvent based undercoat.. just as good(?)

O/P I'm not sure that the zinsser 'bin' will stop rust stains.

Good luck..

Copperface · 25 Jul 2010

Don't know what Zinsser 123 is......another type of sealant/primer?

So, some sort of rust eater, then a zinsser sealant then paint?

Do I have to clean the old streaks off first or can I just paint over them do you think??

?getting more complicated..........

roughcaster · 25 Jul 2010

I've just Googled Zinsser 123, and it says it's a "stain eater",,, sounds good stuff though, maybe worth a try.

jondecs · 25 Jul 2010

I would try the rust converter and spot prime all the area which turns black/ blue dpending on what rust eater you find (halfords etc) with solvent based undercoat. I use 123 lots nowadays might b worth looking at this.
http://www.zinsseruk.com/Shop/Product.aspx?cId=130&pgId=355

Bournemouth pier railings were primed with the stuff lol.

the shellack bin is best on knots/nicotine waterstains.

hope it helps.

jondecs · 25 Jul 2010

oh u beat me r/c

roughcaster · 25 Jul 2010

No probs John,, great minds think alike.

Copperface · 25 Jul 2010

jondecs said:
I would try the rust converter and spot prime all the area which turns black/ blue dpending on what rust eater you find (halfords etc) with solvent based undercoat. I use 123 lots nowadays might b worth looking at this.
http://www.zinsseruk.com/Shop/Product.aspx?cId=130&pgId=355

Bournemouth pier railings were primed with the stuff lol.

the shellack bin is best on knots/nicotine waterstains.

hope it helps.

OK going to follow this advice - however the 1-2-3 is a water based undercoat, not oil based?
so
1. Rust converter
2. Solvent based undercoat
3. Zinsser 1-2-3
4. repaint patch with the sandtex masonry paint

Sound about right??
2.

joe-90 · 25 Jul 2010

roughcaster said:
No probs John,, great minds think alike.

"...and fools rarely differ!"

(Great old Scottish saying - my dad came from Kirkaldy.

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Stains coming through painted render, see pics - what is it?

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