ASK THE EXPERT

Douglas Kent, technical and research director at the Society for the Protection of Ancient Buildings, answers your renovation queries

QWe own an old cob cottage in Devon and need to carry out repairs to the walls – what formula should we use?

I’d suggest a mix comprising soil from the original source, otherwise one with matching constituents. Straw remains an important ingredient, but cow dung, which was often incorporated historically, can be omitted. Other additives are sometimes included, depending on local practice. Lime has been incorporated in recent times but is now avoided because of the unsuitably strong mix produced. Reconstituted earth from the building being repaired can be used unless it is contaminated, for instance, by vegetation. Fresh straw will be needed and, where required, the mix can be modified by the addition of aggregates at one end of the scale or clay at the other. It is sometimes worth having the salvaged material analysed first.

QOur original stone flooring is flaking and chipped. What do you suggest we do to restore it?

Your most feasible option would be to simply dress back loose material where the stones are flaking, although laminations in limestone can sometimes be repaired by conservators using injections of lime-based grout. Take care to minimise damage from vacuum cleaners. Suitable matting can lessen further deterioration. Where there is heavy erosion, you may be able to lift and reverse stones to avoid replacing them. While any deep holes or chipped edges can be filled with hydraulic lime mortar, ongoing maintenance is likely to be required. Renewing part of a stone with matching new material is usually preferable to wholesale replacement.

QMy old leaded light windows are leaking – what can be done to stop the water from coming in?

Establish first that leakage rather than condensation is the source and that it doesn’t indicate an underlying problem. Leaks are sometimes addressed by repairing joints that have opened between glazed panels or around the window perimeter. Often leaks develop between the glass and cames due to decomposition of the glazier’s cement (traditionally a mix of linseed oil, whiting and other ingredients). Successful regeneration of the old cement in situ can be achieved by brushing on several applications of a 50:50 boiled linseed oil: turpentine mix.

The Listed Property Owners’ Club will be providing access to a host of experts and support at the Scottish Listed Property Show, at the Assembly Rooms in Edinburgh on Saturday 27 October. Tickets are £10 in advance at lpoc.co.uk, or £15 on the door