Drying flooded old buildings

Flooding may not be making the headlines anymore but there are still plenty of people with homes that have suffered damage. What worries me is that I’m hearing about insurance companies, loss adjusters, landlords and contractors who are pushing ahead with inappropriate and rushed work to older buildings without thinking about the long term consequences. These may be more harmful than the flood itself.

Speed but not haste is the key. Buildings must be allowed fully to dry out and care must be taken to ensure moisture is not trapped. Sealants, tanking plasters, ‘plastic’ paints and water-repellent products are not the way to overcome flooding or damp in old buildings. They simply compound the problem, causing deterioration of the building’s fabric and potentially resulting in moulds and spores that can lead to ill health for the occupants.

Old buildings need to ‘breathe’ and this means using lime plasters, renders and mortars and ensuring there is adequate controlled ventilation. Indeed, it’s worth remembering that old buildings built and maintained with traditional materials can be much more resilient to flooding than modern ones. Lime-based plasters usually soften when wet but generally harden again when dry, whereas modern gypsum-based plasters deteriorate when wet and will need to be removed.

These are some of the key points to remember when dealing with an old building after a flood:

• Care and time are needed when drying out old buildings
• Monitor the drying out process regularly to check that damaging shrinkage and movement is not occurring to the building’s fabric
• Aim to retain as much of the building’s original fabric as possible
• Get professional advice from specialists qualified to deal with old buildings
• Avoid using pressure washers as they cause damage and blast contaminated matter into the air
• First encourage natural ventilation by opening windows and using fans to promote air movement. At the same time ensure the property is secure – if necessary, fit temporary grilles to openings
• Then, if safe to do so, use steady background heating and dehumidifiers but avoid dehumidifiers if historic wallpaintings are present. When using dehumidifiers close external doors and windows
• To help drying where suspended timber floors are present, lift a limited number of floorboards (take care not to damage them as they’re likely to be swollen by the damp) and ensure airbricks are cleared of silt
• Avoid stripping original plaster. Where it’s necessary to temporarily remove joinery and other architectural elements, number and record the position of the items as they’re removed. Turn timber pieces regularly to limit warping.
• Don’t discard items until you absolutely sure they can’t be conserved. They may, in any case, serve as a useful model to create replicas or when trying to find matches
• If salt deposits, ‘efflorescence’, appear, brush or vacuum them away, never attempt to wash them – this will only make matters worse
• Don’t repair or redecorate until you’re satisfied that the building is dry. When it is use appropriate breathable materials
• Remember with listed buildings to ensure you have listed building consent for any works

Image: Background heating and dehumidifiers can help dry out buildings after flooding Credit: ©Roger Hunt