Ask the Expert Question-and-Answer Archive

by Ron Joseph

January, 2003

Repairing Rusty Steel Flashing

Q. I live in basement flat. In the front bay window, on one of the walls, the metal flashing (used to define the edge when plastering) has started to rust and has now pushed through the plaster and emulsion. Is there any treatment that does not require full replacement and plastering? There is no need to provide additional DPC, the area is quite localised.

A. Since I can't see the problem I will make some assumptions. However, it seems to me that the best way to approach this is to sand the plaster and paint back down to the bare metal. Then sand off all the rust and make sure that you go beyond the boundaries of the rusted area. If the rust is the typical red/brown rust that we associate with steel, then ask your local hardware store for a small can of an alkyd zinc chromate primer. Apply one coat of the primer to the bare, clean metal and allow it to dry for at least one day (depending on weather conditions.) Once the paint is dry and cured apply a coat of plaster and follow with the paint to match the surrounding area. If the damaged area is small, you should be able to accomplish this quite easily.

After you apply the plaster, wait at least one day for the plaster to dry and cure before applying the acrylic latex paint.