ASK THE EXPERT

Q The lead on the front windows of my 1920s cottage (which I replaced eight years ago) has badly discoloured. The original 100-year-old windows at the back are still fine. What is causing this and should I try to fix it?

The building conservation world has been intrigued by an increase in brownish surface discolouration on leadwork over the past 20 years. This has been noticed on lead roofs and vertical lead cladding - but this is the first case I know of affecting window leadwork. Analysis shows that the discolouration is linked to the formation of lead tetraoxide through a conversion of the natural grey surface patina. However, it is superficial, so does not appear to shorten the life of leadwork. While it is not fully understood, the cause may involve petrochemical additives or airborne fertiliser dust. You can remove the discolouration with a mildly abrasive scouring pad and cleaning with water.

Q Water tracks down into our fireplace via the chimney pot and metal lining. What’s the best way to combat this?

With old flues that have no lining, moisture is absorbed by the permeable lime parging in the upper part of the chimney, which evaporates with the warmth of the gases. Modern metal liners, however, can act as downpipes, conveying water down to hearths. Thankfully, fitting a metal rain cap with bird guard into the top of a pot is an easy fix and can be powder-coated to match. Some lining manufacturers’ warranties are only valid with a rain cap as it prevents corrosion. Rain caps must be avoided in thatched homes, though, as the ejected embers increase the fire risk.