Rust stain on render

[Alan Zoff]

As you will see from picture, the wall of the house has a large rust stain. Apparently, years ago an iron chimney ran up the wall. I would appreciate suggestions for obliterating it. It shows through ordinary masonry paint. It is deeply embedded in the render so can't physically remove it.

[IMG]http://i225.photobucket.com/albums/dd192/Alzoff/MumspicturesJune07149.jpg[/IMG]

 

[Chancer]

Try WD40 or the French equivalent, it has worked wonders for me in the past on other problem stains.

Make sure that you throughly degrease before repainting, also try an isolating primer before the masonry paint.

good luck.

[gers32]

if i was you drill a hole in the worst place see if there is any bolts under the render if so remove as much as you can if you was to use wd 40 try a sample on a little patch it might mean removing some render to extract the rust but looking at it it be worth it

[BIG MAC]

I agree it's a good idea tocheck there isn't any more iron in there. WD40 as a rust removing agent I havent heard of, it's a penetrating oil so getting rid of it to allow painting after may be a bit of a nightmare IMHO. I guess I would try removing what Iron remained and making good locally then use a weak solution of dis clean or similar brick cleaning acid try to locally clean up and neutralise the iron without disolving the stone / render. I would then use a masonry stabiliser and two good coats of decent quality masonry paint.

[Alan Zoff]

Thanks for suggestions so far.

I am quite sure there is no iron under the render. Fixing bolts seem to have been removed and holes filled with concrete.

You can just see in the picture the large hole, also filled in with concrete, at the bottom of the stain where the flue originally came through the wall. It apparently then fed into a large pipe that ran up the outside wall, linking with another shorter one from an upstairs room before disappearing through a hole (still there) in the eaves. I assume it was ripped out when they installed central heating some years ago (boiler in cellar, flued to the brick chimney on other side of house, and radiators in all rooms).

[chirpy]

Ask for a solvent based sealer and use two coats to seal in the remaining stain before using the topcoats-if not sealedin the stain will eventually makes it way to the surface-maybe not this year but  after the affect of rain ,sunshine and flexing of the building.

[nomoss]

Oxalic acid crystals dissolved in water removes rust stains from fibreglass boat hulls.

It may be worth a trial, but might not be effective on masonry.

[Alan Zoff]

I'll give the various suggestions a go. If it comes through again in a year or so, I will just have to hack off the contaminated render and re-render it. Or I might just do that now and know that it's sorted once and for all...

Thanks again.

[buckdendave]

As Nomoss has said, try oxalic acid - it removes rust stain from lots of things.

Dave