Modern buildings are usually of brick with a cavity wall to keep the damp from internal walls. Traditional properties are often made of stone and do not have cavity walls or a damp proof course.
The temptation is to seal the wall so that damp cannot get in. This is a bad idea. Damp needs a way to get out. That is, the walls need to be able to ‘breathe’. If damp is trapped in the wall this can lead to fungus and mould problems, dampness inside the building and, when the frost comes, damage to the stonework itself.
All of these are problems that can be expensive to fix, so taking steps to avoid them will save money in the long run.
Traditionally, steps are taken to protect the walls in other ways. Gutters and parapets stop water from running down the walls from the roof and sometimes the walls are limewashed.
In a heritage location, such as Hamilton Square, following the original design criteria ensures consistency across the site and preserves the original look and feel of the area.
In order to avoid expensive re-working, be sure to get council approval for any work to the outside of the building, and especially to the facade.
Repairing rendered, pebbledash and harled surfaces
Possible problems
- An inappropriate render has been used
- Blown render, harling or pebbledash
- Cracks
- Plant growth
- Water leaking into the property
Inappropriate render
Surfaces that have been rendered, or repaired with cement, need attention. The cement based render, pebbledash or harling must be removed and replaced by a limecrete based alternative. This will blend in better with existing wall covering and ensures the wall can breathe, avoiding damp and frost damage in the future.
Blown render harling or pebbedash
The existing material must be removed. Also check whether the surrounding area is of limecrete or modern cement. If it is of cement it should be removed too. The entire surface can then be restored using limecrete render, harling or pebbledash as appropriate.
Cracks
If small, can be filled with limewash and limecrete.
Plantgrowth
The existing render must be removed, the plant removed and any remaining parts treated with herbicide. Where the wall was rendered before it can be re-rendered. If the surface was unrendered, you should seek professional advice as to whether a repair can be effected or the stonework needs to be replaced.
Water leakage
Water leakage is often associated with blown render. Fixing the render problem may well fix the leakage problem too. Water leakage problems generally need professional advice.
Repairing painted or limewashed surfaces
Surfaces in heritage buildings are usually either unpainted or painted with a (possibly coloured) limewash.
They should never be painted with modern waterproof paints because this traps the dampness inside the stonework.
If the surface was originally unpainted it should be restored to an unpainted state. If it was originally limewashed, a similar limewash may be applied once the surface is clean, stable and dry. Basically, you are aiming to bring the surface back to the state it was in when it was constructed.
- Unsuitable or damaged paint should be removed first using a stripping method which is council approved. Typical methods include
- poultice
- steam cleaning
- pressure washing
- clean and neutralise all chemicals after stripping
- ensure the surface is stable and dry
- cleaned away mould and fungus using an approved anti-mould treatment. Approved treatments work without damaging the underlying stonework and ensure there is no water damage inside the building.
The type of finish that can be applied once the paint has been removed is different for commercial and other properties