Many people go to the expense of re-roofing their home when all that is necessary is treatment of the weatherworn galvanised iron. Rusted but sound metal can be restored with a rust converter, a paint on product that turns rust back into solid metal. Corrugated iron that has lost much of its protective galvanising can be treated with an inhibitor that will prevent the formation of rust.

Specific treatment of a deteriorating corrugated iron roof depends on the type of system adopted by the manufacturer of your favoured brand of paint. Each of these systems is effective; the need is to follow the recommendations faithfully and, above all, to avoid mixing brands of paint. The top coat of one manufacturer, for example, may not be compatible chemically with the undercoat of another manufacturer.

[edit] Dealing With Rust

Remove all loose rust, powder, chalk and dirt with a wire brush. Remove oil and grease with turps. Apply rust converter, which is a watery liquid, only to areas that are rusted. The metal, of course, must essentially be sound. Next, treat areas that are not yet badly rusted with a rust inhibitor. Allow 24 hours for the anti-rust solutions to dry out.

Having treated the rust, the need is to ensure that the surface of the roof is in a condition to give good paint adhesion. Some manufacturers recommend that the entire roof be swabbed down with hydrochloric acid to thoroughly etch the iron: others by pass this step as their product is based on a formula that takes care of the problem.

If hydrochloric acid is used, hose down the roof before painting.

The easiest way to paint a roof is with a roller on a long handle. The rollers are made of plastic foam and are shaped to fit two or three corrugations. Those moulded in one piece stand up to the work better than the rollers composed of sections. There are also wire brushes for cleaning off rust and old paint that fit the corrugations.

Most paints recommended for old roofs are oil-based, and many contain rust inhibiting chemicals. A primer may be recommended for the entire surface of the roof, but at least one major manufacturer recommends a red oxide zinc chromate primer only for the rust treated areas. The undercoat is extremely important, as it has qualities that enable it to adhere to a galvanised surface. Unless stated otherwise, allow 24 hours between coats.

The range of colours of paints designed specifically for roofs is limited to standard shades of red, •green, grey and brown. But they all look attractive. Your choice may depend on the character of your house. There is also a brilliant white (the best colour for reflecting the sun's heat), but it can be an annoyance to neighbours.

Anti-corrosive paints with builtin rust inhibitors are also used for guttering and downpipes. As well, they are ideal for painting iron gates and fences and any iron work around your home that needs protection.

[edit] Painting A New Metal Roof

If you should choose to roof your house with unpainted corrugated iron sheeting rather than pre-painted, wait for six months before doing the job. This is advisable to create a surface that will give maximum paint adhesion. Exposure weathers the shiny, slippery surface that rejects paint and also gets rid of the greasy film found on new iron. Even after a period of months, thoroughly clean the roof before painting. Wash down the entire roof with turps, and if you intend using water based paints, swab off the turps with detergent. If the metal does not seem to be greasy a strong detergent wash might be all that is needed.

Before painting, read the general advice given above in Painting an old iron roof and religiously follow the paint manufacturer's recommendations. Water based acrylic paints are becoming increasingly popular for roofs: they are easy to apply, the primer can be painted over within four to six hours and you have a wide range of colours to choose from.

But a word of warning to country people dependent on roof catchment for their water supply - Do Not Use acrylic paints as they will contaminate your drinking water. Aluminium roofs are painted in the same way as iron roofs, but it is important to use a special alumin­ium etching paint as a primer (yellow zinc chromate).