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Painting Metal Windows

Method of Removing Old Paint: Rust Removers : Protection from Condensation
By Ray Lewhite.

Most metal windows in older houses are made of iron, and when new were treated at the factory with a coating of zinc; they are known as galvanized iron windows. (Crittall windows were installed by the millions) The zinc coating protects the iron from water and so prevents it from rusting. Often however, some of the older houses have iron windows which were not galvanized and the iron has become wet through steam and condensation running down the glass and rusting has carried on for many years. On the other hand, because of age or neglect, the zinc coating on galvanized iron windows may have become thin or broken and rust has been produced beneath the zinc coating, causing it to lose its grip upon the iron. Exactly the same thing happens with paint films upon iron windows which have rusted. The rust will creep beneath the paint causing it to turn brown and later push it off.

Removing Old Paint

Painting Metal Windows
Where the old paint is in a very dilapidated condition it may be removed fairly easily with a painters stripping knife or a shave hook. It is very seldom that the rust is so firmly attached that it would be necessary to use a cold chisel and hammer. On some parts of the window especially where it is not effected by moisture, the paint may be in a sound condition and need not be removed. If there is any doubt then treat it with liquid paint remover. This should be liberally applied with a small brush and time allowed for it to soften the paint. When it has reached this condition it may be scraped off. Should the paint be very old and thick, a second application of paint remover must be applied in order to expose the bare metal. Coarse emery cloth should now be used and all the bare metal, especially the rusty parts, should be vigorously rubbed, starting at the corners of the frame and working towards the middle parts of the bars. As soon as this operation is completed the bright metal should be treated with a metal primer.

Rust Removers

Painting Metal Windows
Where metal window frames have been neglected for many years and rust has continually formed, it will be extremely difficult to completely remove it from the metal, even with the coarsest of emery cloth and the maximum physical effort. In cases such as this the rust must be converted into another substance which has no detrimental effect upon the paint that is to be applied. There are solution obtainable in small bottles called rust removers. This is actually a misnomer, for it does not remove the rust but converts it into a phosphate which is hard and firm and suitable to support coats of paint. So after removing as much rust as possible, apply the rust remover with a small brush and wait until the rust has changed to a dirty greyish colour. Because rust remover is a acid care should be taken not to apply it or slash it upon surrounding paint which is not going to be repainted. There are special paints on the market designed to be applied upon bare metal. Their main function is to inhibit the spread of rust, and to gain firm attachment to the bare metal. One of the best types of primers is zinc dust primers obtained in small tins sufficient to paint an average size window. This primer prevents metals rusting by electrolytic action, and in order to ensure is complete the metal window frame should be rubbed down with emery cloth and made very bright in patches approximately 6in. apart. Furthermore to ensure that the circuit is complete, it is best to moisten the metal frame with water before the zinc dust primer is applied.

Primers

Painting Metal Windows
Another rust inhibitive primer was red lead but this has been outlawed and replaced by zinc chromate, and is suitable for metal window frames and should be applied to clean metal, free of rust, with a paint brush of a suitable size. When painting protect the glass with masking tape, which should be removed after the window frame has been completed with its final coat. The primer should be applied as evenly as possible, making certain that all parts are adequately covered, including the edge of the bars were they meet the glass. Under normal conditions the primer should be dry within 24 hours.

Condensation

Painting Metal Windows
Most windows suffer from condensation, and precautions should be taken to prevent water from getting behind the metal bars. All lose putty and that which is broken should be removed and replaced with new putty. Linseed oil putty is the material to use, which should be rubbed in the palm of the hand until it is soft and pliable and forced into the cracks between the glass and the frame with a stopping knife or old table knife. The putty in the bottom rail should be levelled off so that the condensed water upon the glass is able to run off. The undercoating should next be applied, starting at the top of the window and working down towards the bottom. When this is dry it may be lightly rubbed down with F2 grade of glass paper. Metal window frames should always be finished with a glossy paint.
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