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Features WINDOW REPAIR


as well as treatment with a solvent-borne preservative. Another problem is decaying timber sills, which can be replaced with thoroughly primed durable hardwood.


Any preservative treatments can be brushed onto the affected area after the decayed wood has been cut out. In some cases, it makes sense to bring in specialists to either pressure-inject organic, solvent-based preservative into the timber or to insert preservative rods containing water-soluble chemicals that diffuse into the surrounding timber.


Another option, and one that is commonly used, is to use proprietary polyester or epoxy resin repair products, which can be a good way to maximise the amount of original fabric retained. This will substantially extend the life of an original window when traditional joinery repairs are not possible.


Repairing metal windows Various kinds of metals are used for window frames. Non-ferrous metals include bronze and aluminium (though aluminium windows are very unlikely to be found in historic buildings). Frames of copper or


bronze can typically be repaired by brazing, soldering and welding, as well as stitching, riveting or screwing the pieces together. Ferrous metals are more common, and the kinds of repairs necessary depend on the particular type. Ferrous metal windows can suffer from surface rust, distortion, excessive build-up of paint and failed hinges and fittings. It's worth noting, though, that corrosion often looks worse than it is, so even windows that appear beyond repair can often be made good either by acid pickling or flame cleaning, adding decades to the window's life span.


Wrought-iron and cast iron windows Wrought-iron frames can usually be repaired with rivets, bolts and tenon joints, or sometimes by welding-on sections of a ferrous non-corroding alloy. Best of all, though, is to use salvaged wrought-iron sections, which should be welded through the full depth of the metal to ensure all parts are connected together and the bond is sufficiently strong, which is unlikely using just surface welds. As for cast iron frames, although welding is technically possible, there is a significant risk of fracturing the metal, so it is recommended that cast iron is


repaired by cold stitching. The surface should be cleaned back to sound metal, primed, repaired and painted.


Steel windows Ungalvanised steel windows are prone to rust and corrosion, which causes the metal to exfoliate and expand, and this can crack the glass. The problem begins when moisture is allowed to penetrate the protective paint, usually as a result of neglected decoration, defective putty or a faulty weather-seal. The first sign is often flaking or blistered paintwork, which should be probed with a pointed tool to establish the extent of the problem and any treatment necessary.


The key decision is whether to repair the window on-site or take it to a workshop, in which case it is important to carefully record its original profile. Severely corroded sections can be cut out and replaced as long as suitable matching sections can be sourced. Only where repair along these lines is not viable should the windows be replaced, and naturally with steel windows of the same kind.


Steel windows made after the mid-1950s are likely to be galvanised, which makes repairs much more straightforward. Nevertheless, it is important not to damage the galvanised finish in the process. It is a good idea to upgrade the window thermally at the same time.


Surveys In all cases where windows are to be repaired, it is vital that an overseeing surveyor draws up a schedule of works setting out the repair methods to be employed. It is usual that a preliminary survey is carried out at specification stage and a more detailed survey undertaken once scaffolding has been erected. The surveyor would usually draw up a schedule of the required repairs to each window and on a flat-by-flat basis. This information would be


Before and after (bottom right): Renovations to timber dormer window in a grade II listed building


44 Issue 21


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