Advice & Guidance

Walls

The UK has a diverse range of building stones ranging from tough Cornish granites through to soft, easily weathered chalk. Limestones, sandstones, slate and flint contribute much to the character of our places of worship as do manufactured materials such as brick and terracotta.

We may also find that our ancient walls contain reused materials such as Roman tiles or early grave markers. The variety in colour, texture and pattern is very importance and for this reason we must take extra care to treat our walls with sensitivity when we maintain and repair them.

New stone following original profile

As different building materials have a range of characteristics and decay patterns we must take time to understand the materials our buildings are made of before we contemplate their repair. We also need to understand how walls are constructed and be alert to the early signs of structural problems.

Masonry: In the main, the masonry elements of the building e.g. the brick, limestone, sandstone, granite or flint will stand up well against the elements and will have a very slow rate of decay.

Weathered stonework However, problems with other parts of the building fabric, such as the rainwater goods, may increase their rate of decay. We also know that the presence of incorrectly specified mortars containing cement can have a damaging effect so it is good practice to examine the wall surfaces from time to time.

Architectural features such as string courses, cornices and hood moulds above windows and doors are designed to throw water clear of the face of the wall. If these features are damaged water will run down the face of the wall increasing the rate of decay. You should therefore pay close attention to these elements.

When looking at the walls take time to consider the condition of the mortar in the joints. Note areas where the mortar is deeply recessed, very crumbly (friable), loose or missing. Your architect or surveyor will be able to advise whether there is a need for some localised repointing.

Decayed joints between the stonework They will also be able to specify a suitable mix for the repointing mortar as it is very important to make sure that the mortar allows any moisture present in the wall to evaporate through the joints rather than through the face of the stone.

Pollution may affect the appearance of buildings in urban areas over time. However, unless the soiling is heavy and is actively harming the masonry, cleaning is usually inadvisable. You should also avoid using colourless water-repellent coatings on masonry.

These have a limited life, rarely provide a cure and can often cause more harm than good.

Traditional render and limewash Render: Traditional renders are generally based on a mix of lime and sand. This makes them softer and more porous than modern cement renders, which can be extremely dense and impermeable. When rain falls on a lime-based render, it is absorbed then dries out naturally when the conditions are favourable. Lime renders are also flexible and will accommodate movement in the structure without undue harm.

Over time, lime renders will weather away, particularly where they are used in exposed locations, so it is advisable to note the condition of the render.

Your architect or surveyor may suggest some patch repairs to repair small areas of damage. Lime render can also be given a protective coating of limewash to help ensure its longevity but avoid using proprietary masonry paints or waterproofing substances on lime renders as these will disrupt the building's ability to ‘breathe'.

Patched cement render In contrast, cement renders are designed to be impervious and will crack if there is any movement in the structure. Such cracks will allow rain to penetrate the wall where it can become trapped and may promote decay. Cracks and areas of missing render should therefore be reported to your architect or surveyor. These can often be successfully patched or consolidated.

Alternatively, it might be worth considering whether the cement render could be replaced with a lime render.

This would improve the building's ability to ‘breathe' but care must be taken, as removing the cement render can cause damage to the fabric underneath. The potential harm to the fabric must be carefully weighed against the benefits of removing the render.

Bricks damaged by removal of cement render

Timber: Throughout history, timber has been used as a structural material in walls, floors and roofs and can last indefinitely if properly maintained. Any problems are usually attributable to dampness, which can lead to fungal infestation and wood-boring insect damage.

Timber repairs Oak, chestnut and certain other hardwoods are generally very durable and grow harder with age. They also have a natural resistance to decay and insect attack. On the other hand, softwoods, such as pine and fir, are generally less durable and need to be painted to protect them from decay. The most vulnerable part of all timber is the outer sapwood. If you suspect that there is timber decay or possible insect infestation in your building, seek advice from your architect or surveyor, rather than someone with a vested interest in a method of treatment. It is usually possible to treat such problems sympathetically. Wholesale timber treatment with chemical preparations is rarely necessary but independent advice from a timber specialist (rather than a treatment company) may be required. Also, remember to ask your cleaning team if they have swept up any insect debris. Evidence of insect attack is often cleaned away and not reported.

Joints, particularly between structural sections or between the timber component and adjacent masonry, can also be problematic. If water is able to penetrate these areas, it can do serious damage, so it is important to check any timberwork carefully in order to spot potential problems at an early stage. A skilled carpenter or joiner will be able to cut out small areas of decay and repair them with a new piece of timber. The distortion of timbers is rarely a problem and is usually attributable to the natural movement that occurred while the timber was drying out.

Shakes in oak beam

Action point: If areas of softwood have previously been painted, make sure that the integrity of the surface is maintained. This will probably mean repainting external timberwork every few years. If the surface is allowed to break down, water can penetrate the cracks and become trapped leading to decay. If your building is Grade I or Grade II* listed you should consider using traditional lead paint as this has a pleasing appearance and is long lasting. If you are not able to use lead paint, you might consider using other types of traditional linseed oil paint instead.

Extensive plant growth Plants: Plants may enhance the appearance of buildings, but consider seeking advice about the control or removal of trees or climbers if there is evidence that they are damaging walls or blocking gutters.

Recent research has shown than ivy can sometimes provide a level of protection to old walls but in other cases it can be quite destructive. If the walls are already in a poor condition then ivy can force joints open and damage the core of a solid masonry wall.

Planted borders around the base of the walls are a popular way to enhance the appearance of a building but do be aware that this may prevent the masonry drying out properly. The presence of large shrubs may also reduce access for maintenance purposes and air grilles or ventilation bricks may become blocked.

Action point: Clear away plant growth from around the base of the building and in particular from the ground gutter or drainage channel. The roots of plants and grasses can damage the integrity of the channel and impair its ability to carry water swiftly away from the building.

It is best to remove weeds by hand rather than using weed killers as the chemicals in the weed killers can penetrate into masonry leading to problems of efflorescence.

If you are unsure how to deal with ivy on your building seek further advice from your architect or building surveyor.

Ground levels: High ground levels can encourage dampness so care should be taken to prevent earth building up against the base of walls. Ideally, external ground levels should be at least fifteen centimetres (six inches) below the internal floor level.

However, it may not always be desirable to attempt to reduce the ground levels around older buildings as this can have a negative impact on burials and archaeological deposits. If this course of action is deemed necessary archaeological advice should be obtained before any ground is disturbed.

Air bricks and ventilators: Air bricks and ventilators are used to circulate air through the voids under timber floors or pew platforms. If they become blocked, there will be less air movement under the floor, which may eventually encourage rot in the floor joists and floorboards. If air bricks or ventilators are broken, replacements can be obtained.

Decorative ventilator Many older examples are decorative as well as functional and should be retained if possible. It is often a good idea to fit some fine mesh behind the ventilator to exclude rodents and insects.

Action point: Make sure that any air bricks or ventilators in the base of the wall are free from obstruction and clean them if necessary. A thin stick is useful for this purpose.

Advice & Guidance

Walls

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