Maintenance
Walls and ceilings of older homes were plastered with lime or lime and earth-based plasters, so carry out any repairs using traditional materials and techniques
Until around the 1930s, walls and ceilings in most homes were plastered using traditional lime or lime and earth-based plasters. Unlike modern cementitious or gypsum plasters, these allow walls and ceilings to breathe and flex and are often mixed with animal hair or hay to reduce shrinkage and offer strength. Historically, this plaster was applied in one to three coats.
Any repairs to these surfaces should therefore be carried out using a compatible mix. Plastering is specialist work: limes are alkaline and caustic and are potentially harmful to eyes, skin and lungs, so wear safety glasses and gloves and, if mixing powdered products, work in well-ventilated areas and wear a good quality respirator mask.
How to repair
Before starting any plasterwork, proper investigation is essential so that the extent of the work is known, advises Julie Haddow of Lime Repair. ‘Plastering is a messy business so protecting adjacent floors and surfaces is very important. Remember, jobs often get bigger because you can’t always see the extent of the repair required.’
Understanding why plaster has failed and fixing the source of the problem before repairing the plasterwork is vital. ‘Cracked renders, missing pointing mortar, roof leaks and high external ground levels can all contribute to dampness and failed plasters on the inside,’ says Ryan Stojic of traditional building specialists Mike Wye. ‘If these aren’t identified and addressed you could end up with the same problems in your new lime plaster.’
Where plaster has been affected by damp and is crumbly or crusty, Julie suggests that it will probably need to be removed. ‘If the damp is caused by a short-term leak, it should dry out and remain in good condition.’
Ryan warns that saturated walls should be allowed to fully dry out before applying a new lime plaster. ‘Otherwise, there is a risk of slow setting – for non-hydraulic plaster – mould growth, and trapped moisture, which may take a significant length of time to dry out once plasters are applied over the top.’
Over the years, cracks frequently develop in plaster. While larger cracks should be investigated in case they result from structural issues, most just require filling. ‘We don’t recommend raking out cracks because, if it is a lime mortar with plenty of hair in it, raking it out will break the tension between the hairs,’ says plastering specialist Sean Wheatley. He advises removing dust from the crack with a vacuum cleaner, dampening it down and then using a soft, premixed filler, such as Toupret. Some prop
