What the 1980s did to our listed buildings

The 1980s were a catastrophe for Grade II listed residential buildings in the South East, and the profession is still arguing about exactly how bad. What is not in dispute is that four specific interventions, applied very widely between roughly 1975 and 1995, caused most of the damage we spend our working weeks trying to reverse. I'll take them in turn, briefly, because every owner of a listed building needs to be able to recognise what was done to their property.

The first is cement render over timber-framed or soft-brick buildings. Cement is impermeable. Timber frames and soft bricks are not — they are designed to take on water in the winter and release it slowly in the spring. Seal the external face with cement, and the water routes through the timber instead. Fifteen years later the frame is soft at the base, the sill beam is structurally compromised, and the owner wonders why the render is peeling off in sheets. It isn't — the cement is being pushed off by the building trying to breathe. On any listed building where the render looks suspiciously smooth and unweathered, assume cement until proven otherwise.

The second is the chemical damp-proof course — that silicone or siloxane injection a surveyor recommended in 1982 because the plaster was blooming at skirting height. In almost every case I have seen, the bloom was condensation caused by impermeable modern paint on the wall, not rising damp. The chemical DPC solved nothing; it added a horizontal band of dried chemicals twelve inches above floor level which, along with the retained cement render outside, trapped moisture in a new and more damaging pattern. If your listed building had a DPC injected in the 1980s, the right answer is usually to strip the modern plaster, remove the external render, and let the wall breathe for a year before deciding what to do next.

The third is gypsum plaster applied directly onto lime-plaster substrates. Gypsum is chemically incompatible with lime over the long term. The bond fails in five to ten years, and the new plaster falls off in sheets, usually taking chunks of the historic lime with it. The repair is always longer and more expensive than the original gypsum job. If a room in your building has been replastered in gypsum over historic lime, factor replacement into your ten-year plan.

The fourth is plastic paint — any emulsion or masonry paint with a vinyl or acrylic binder — on external lime-rendered or cob walls. The mechanism is the same as cement: it seals the surface, water routes behind it, the render or cob softens, and eventually the paint peels off in sheets with a layer of the underlying material attached. The repair is always a chemical strip and a return to lime wash.

The good news is that none of this is irreversible if caught early. The bad news is that a whole generation of owners were told these were improvements, and the correct specialist knowledge to undo them was, for a while, genuinely hard to find. It's less hard now — the SPAB runs excellent courses, the Heritage Craft Association publishes good guidance, and firms like ours exist specifically to rebuild the knowledge that was lost. If you own a listed building and any of this sounds familiar, write or ring. The first site visit is free.