Guide: Historic Metal Casement Window Care, Repair and Maintenance

With care and routine cleaning historic metal casement windows can last just as long as a modern-day replacement. Whether cast, wrought iron or steel, corrosion is generally the primary cause of any issues that might occur.

This guide aims to give a historical context to non-galvanised (pre-1950) metal casement windows and the distinct development of material and form over the years, advice on a best practice maintenance routine, signs of deterioration to look out for and likely restoration and repair techniques when metal windows are in need of intervention.

Whilst every effort has been made to ensure this guide is informative, this is not a definitive resource to historic metal window restoration and specialist advice should always be sought when necessary. 


Metal Casement Windows Through the Ages


The first metal windows in the UK were reserved for the noble or papal. Exceptionally expensive, glazing was not affordable for most meaning the earliest examples of metal windows in the UK are predominantly found in ecclesiastical buildings and country manors.

Initially, windows were made by medieval blacksmiths from wrought iron. Installed directly into the building secured with copper or lead ferramenta bars, the windows were fixed closed and fairly simplistic in design. 
Casement windows, those with at least one light or pane that could be opened, required significantly more skill and craftsmanship since they required mechanical components.

The majority of 14th – 17th-century windows took this form, made up of a series of leaded light panels, in diamond shapes (known as quarries) joined together using strips of lead (cames) to produce one casement glazed area framed with wrought iron.

In the 18th century, wrought iron casement windows were predominantly superseded by the latest fashion - timber sash windows which we see so much of today.

Still, metal casement windows with leaded lights continued to be used in ecclesiastical settings and in lowlier domestic houses, and a mini-renaissance occurred in the 1800s with the boom in gothic architecture, the arts and crafts movement and the industrial revolution.

The developments in manufacturing processes in the industrial revolution led to traditional wood sash windows being reproduced in cast iron. Once a craftsman’s job, metal windows could now be mass-produced by the new 19th-century factories.

The final stage historically in metal window development came in the 1850s when Sir Henry Bessemer, an English engineer and inventor, developed a new mass-production process for hot-rolled steel.

This allowed for new innovations in the manufacture of casement windows and as a result, they became predominantly made from steel. Through the Art Deco and World War periods, owing to the versatility of the material architecturally, steel window production flourished. One of the largest and most well-known producers of the time was Crittal – now a well-used term for steel windows – which is still in production to this day.

To find out more about the metallurgy and a historical context of the particular metals used in these windows have a look at our tech spec guides for wrought iron, cast iron and steel.



Maintenance and Care


In the case of older non-galvanised metal windows made of wrought iron, cast iron or steel, a maintenance routine should be developed to ensure your windows last as they should.

Some of the most prevalent problems that occur with metal casement windows include:

  • Distortion
  • Build-up of paint
  • Hinge and fitting failures
  • Excessive corrosion 

Corrosion, although slightly different depending on the fabric of your window casement, is generally the primary cause of any issues that might occur, and good care and routine cleaning will keep this to a minimum, protecting both the metal and glazing.

If in any doubt, seek professional advice before attempting to clean metal windows.



Routine Inspection and Cleaning

  • Check metal frames for sitting water – whether resulting from heavy rain or condensation. Gathering excess can accelerate the corrosion process.
  • Some steel casement windows will have small holes along their base (weep holes) to allow sitting water to drain away. Check these regularly for blockages and keep them clear of any obstructions
  • Light rust can be removed by hand with a wire brush or sandpaper, however, more severely corroded metal windows may need to be cleaned professionally.
  • Oiling moving components of window furniture regularly will help reduce the chances of rusting or fusing shut. A thin oil (such as 2 in 1) should be used on iron and steel window moving components to keep them free.
  • You can clean historic ironmongery gently with soft cloths or brass brush. Do not use any abrasive cream or solvents and ensure you dry the ironwork completely after cleaning. 



Signs of Windows in Need of Intervention


There are certain signs to look out for that may indicate some of the above conditions may be occurring, at which point, restoration/conservation advice should be sought.

  • Fusing between catches, stays and pivots (never force windows open or closed if they are stuck!)
  • Blistering to protective paintwork where metal underneath is corroding
  • Lifting/falling out of putty around glazing
  • Localised cracked glass and/or split masonry
  • Distortion occurs due to thinning sections of a metal frames



Typical Restoration and Repair Techniques

Often, metal casement windows will look a lot worse than they actually are. Since rust by volume is greater than un-oxidised iron or steel, what looks like a terrible mess may in fact be fairly easily rectified by a professional. Once restored, metal casement windows can last as long as a new replacement would if maintained.

Original historic metal windows bring character and aesthetic to your building, and should never be replaced with uPVC or other crude alternatives. Replication, where repair isn’t possible, should be sensitive to the character of existing windows using matching sections, original fittings, and where necessary, traditionally produced glass.

An important note should be made on window furniture. It is of great importance that the existing furniture is both maintained and preserved where possible and re-used during any repair or alteration works.
These points are even more relevant where the building is listed or in a conservation area and planning consent may be required.

In restoration, glazing and old putty will often need to be removed from the metal frames.  Existing glazing will be carefully cleaned and reinstated and replacement putty installed.

Where the metal frames are in need of attention, dependent on the fabric, dent-straightening, cold stitching (if thick enough), fire welding, modern welding and patching are typical repair techniques which may be used.

Whilst light corrosion can be removed by hand, serious rust may require using acid pickling or shot blasting. Which techniques are employed will often depend on both budgets and the historical context of the windows.
A zinc-based paint will often be used as a primer to provide a protective layer to bare metal prior to painting with a suitable system.

It should be noted, that removing all coatings from the metalwork can destroy evidence of previous historic paintwork. As such some paint samples should be taken and if possible layers should be left behind in a small area where rust has not occurred to provide a context for future owners.

These restoration methods should only ever be carried out by a skilled and experienced professional. 

Click below for guides on other architectural metalwork features: