Ask the Expert Question-and-Answer Archive

by Ron Joseph

July, 2004

Surface Preparation of Rusty Galvanized Roof

Q. I have an old galvinized metal roof on a barn that has become rusty. Its over 6000 sqft so I'd like to paint it with inexpensive aluminized fiber asphalt based coating. Hand sanding and prep is too daunting and time consuming on such a large area. I was thinking of spraying with a phosphoric rust converter, pressure washing to TSP, then priming. Is this adequate prep and which primer should I use to keep the costs down?

A. Preparing the roof with the rust converter is a good idea but if the rust is heavy it may require several applications. The asphalt based coating will provide excellent protection even over rusting metal, as a matter of fact, the rust texture will promote adhesion. The power wash and TSP will clean as well as remove the residue from the rust converter.

Best regards,

Tom Burke