After a pipe leaked in an upstairs bathroom and the plaster in the wall downstairs, above the kitchen window, became wet. A metal strip just under the surface of the plaster became corroded (it looks like rusted iron) and this flaked the top layer of plaster off. This is along the edge of the underside of the window (where a concrete lintel might be expected to be, above the window).
The rusty metal is exposed in only two places and these are 2 to 3 inches wide and a quarter inch or so high. The pipework is long fixed and the wall is fully dry. I need to decorate the kitchen.
How should I treat the rusty iron in order to then fill or plaster over it? I guess there is a product that will seal it but I can find no information on how to proceed.
It is quite a small repair but I don’t want the rust to lift or stain through what I put over it and I am guessing that putting wet filler onto it will reactivate the rust.
The steps I would take in this situation would be:
- Ensure all traces of damp have been eliminated and the affected area has fully-dried out.
- Cut back the affected plaster beyond the rusty area and, if possible, remove the rust with a scraper and/or a wire brush and abrasive paper.
- Prime all the exposed metal with an oil-based metal primer with zinc content. (Zinc-phosphate, ideally, and 2 coats are better the one).
- Allow to dry for at least 48 hours then repair as normal and redecorate.
Hope this helps although there is always a risk that there has been some damp contamination in areas you can’t see (such as the other side of the metal beam) and this will eventually work its way through to the surface.
However, it is almost impossible to mitigate against this and you will just have to wait and see.
That said, any minor staining that does eventually work through can be treated with a coat of the same metal primer before redecorating.