ASK THE EXPERT

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

Q How should old lime plaster with surface damage be treated?

Small pockmarks and minor damage can be filled with either matching lime plaster or, if they are narrow, interior filler gauged with whiting (pulverised chalk). Lime plaster, however, is preferable where repairs will be limewashed. Another option is to conceal blemishes below new lining paper, providing there are no important historic finishes. Occasionally, a new coat of lime plaster might be skimmed on, particularly over small areas, but skill is needed. Where areas of plaster, especially those of historic importance, lose cohesion and become powdery, specialist consolidation techniques can be used along with materials such as nano-lime (fine particles of calcium hydroxide suspended in alcohol).

Q What can I do about draughty or rattling sash windows?

Good draughtproofing (including new parting and staff beads with seals) will address draughts and rattles from general wear and tear. Alternatively, fit cam-action catches or, as a temporary solution, small timber or rubber wedges. Tackle draughts or rattles due to badly positioned, insufficiently thick or distorted sash beads by repositioning or replacing them. Excessive wear of timber parts results in sashes moving too freely and their overlapping horizontal or ‘meeting’ rails settling out of level. Remove any projections causing wear and fill grooves with filler. In severe cases, re-edging of sashes might be needed. A gap above a sill may indicate a structural problem, requiring other work.

Q Should I clean old stonework?

Cleaning is sometimes justified but often does more harm than good, damaging stonework and erasing evidence of a building’s history. Cleaning may be appropriate, however, where there is a need to facilitate repairs, or remove stains, soiling or salts contributing to decay.

The method and extent of cleaning must be carefully chosen in consultation with a specialist depending on the deposits and stone type. Don’t over-clean and be mindful that some techniques, such as aggressive abrasive cleaning, can be very damaging. A trial should always be conducted first.