Although you will probably want to leave major wall repairs to a professional, there are some jobs you can do yourself.
Even if your outside brickwork is sound, it will benefit from an occasional scrub down with a stiff broom and clean water. Mould or algae can be removed by scrubbing the surface with a mixture of household bleach and water, but a fungicide is better. Efflorescence, a surface deposit of powdery white crystals caused by water penetrating the brickwork and then evaporating and bringing dissolved salts to the surface, should be brushed off from time to time; washing it off only causes the salts to redissolve and reappear at a later date.
Replacing damaged bricks
Brick is porous, absorbing moisture when the weather is wet and allowing it to evaporate when the weather is dry. On very porous bricks, water may accumulate in the brick and freeze in cold weather, causing the surface of the brick to break away or spall. Such damaged bricks need replacing.
Use a club hammer and brick bolster, cutting back until you reach the solid brick behind, in a solid brick wall. Cut a new brick in half along its length, and bed it into the hole with a thick mortar backing, so that its surface is flush with that of its neighbours. On a cavity wall one brick thick, you will have to loosen the pointing around the damaged brick, and then use a narrow cold chisel to lever it out. Where necessary, you will have to break up surrounding bricks. Then line the opening with mortar after chipping away all the old mortar, and tamp the new brick into place. In either type of wall, finish off by pointing around the new brick for a weatherproof joint.
Even if the bricks themselves are sound, you may find that the mortar pointing between them has begun to crumble and fall out. If this is the case, use a club hammer and cold chisel or mortar rake to chop out the old pointing to a depth of about 18mm (3/4in) and then brush out all the dust and debris. Soak the brickwork to stop it absorbing all the water from the new mortar. Mix up enough mortar (1 part cement to 4 parts soft sand) for about two hours’ work, and start at the top of the affected area, taking mortar from a hawk to fill the crevices between the bricks. Press the mortar firmly into place, and trim off the excess roughly as you work. When you have completed a reasonable-size area go back and finish off to match the rest of the wall.
Flush pointing is left until the mortar is almost dry, and then the excess mortar is rubbed off with dry sacking. Weathered pointing is formed by drawing the edge of the trowel along the top edge of each horizontal join, and either the right-hand or left-hand edge of each vertical one — it does not matter which you choose as long as you are consistent — to leave a sloping surface to the pointing. A raked or recessed joint is scraped out with a pointed rod, while keyed pointing is given its rounded shape by drawing a dowel rod or a shaped piece of metal along the pointing. The final touch is to brush off the last traces of mortar with a stiff brush.
Rendering is a layer of mortar applied to exterior brickwork or blockwork as decoration or weatherproofing, and may be given a smooth or textured finish, or may have pebbles or fine shingle bedded in it. Once the surface begins to show cracks, moisture can penetrate and cause more widespread damage, eventually causing large areas to crumble and fall away from the masonry surface. It is therefore essential that any rendered surface is kept in good condition.
Undecorated rendering or pebbledash, however sound, soon begins to accumulate dirt and to discolour, and will benefit from an annual wash and scrub down with water and a stiff brush. Decorating with masonry paint or exterior-quality emulsion paint will enhance the looks of the surface, and
will also help to protect it by sealing the surface, so preventing dirt from adhering to it so readily and also cutting down on the rate of water absorption. Small hairline cracks should be filled with exterior-quality filler before they have a chance to enlarge and allow further deteriorating.
Where areas of rendering have crumbled away, you must chop out all loose material back to a sound edge before attempting a repair. Loose material should be brushed off and the wall surface damped ready for the first mortar coat, which should be applied with a float so that its surface finishes about 12mm (1/2in) below the level of the existing rendering. It should be scored when almost set to provide a key for the second coat. Leave the first coat to set for 24 hours, and then apply the second layer slightly proud of the surrounding surface. Draw a batten over the surface of the existing rendering and the patch to remove excess mortar, using a sawing to-and-fro motion. The surface can then be polished with a steel float if a smooth finish is required, textured to match the wall or covered with pebbles pressed into the final coat.
If you have to re-render an entire wall the technique is broadly similar to that for patching. It is best to divide up the wall surface into bays by pinning battens the same thickness as the final rendering — usually about 20mm — to the wall surface. Make the bays a maximum of 1.5m (about 5ft) wide. Then apply the mortar in two or three layers, cross-hatching the surface between layers to provide a key for the next layer.
Rising damp is moisture rising up the house walls from the ground as a result of failure in, or absence of, the damp-proof course of impervious material just above ground level. The result is a band of staining on inner walls, rising well above skirting board level in some cases, causing wallpaper to peel and adjacent timber — floors, skirting boards and so on — to rot. It can be cured only by inserting a new damp course, which can be done by one of several methods, most of which are usually professionally installed.
The first is the insertion of a new damp course of felt or slate. This is done by using a power saw rather like a chain saw to cut through the wall — usually along a mortar course. The damp course is inserted as the slot is cut, and is mortared into place. Both leaves of cavity walls must be treated.
The second method involves drilling holes in the wall at regular intervals, and injecting special chemicals which are absorbed into the masonry and dry to form a damp-proof barrier. Again, both leaves of cavity walls must be treated. The fluid can either be injected under pressure, or else allowed to flow in under gravity.
The third method is called the electroosmotic method, and involves inserting a ribbon of copper wire into the wall at the required level. This is then connected to a copper earth electrode driven into the ground. This method works because a small electrical charge is associated with the rise of water droplets up the wall, and the copper strip discharges these to earth, so preventing the droplets from rising. It is installed by damp-proofing contractors.
It is worth remembering that rising damp can also be caused by the damp course being bridged, allowing moisture to bypass it. The commonest cause of this is earth from flower beds being banked up against the house wall, but adjoining paths with their surfaces next to or even above the damp course can have the same effect, as can garden walls abutting the house wall without a vertical damp course between the two.
Solid floors should incorporate a damp-proof membrane too. If this is defective or absent, the floor surface can be sealed with a damp-resistant pitch-epoxy chemical, but this must be linked to the damp course in the walls. If this is not possible, the floor will have to be lifted and a new floor laid over a damp-proof membrane of heavy-duty, 500-gauge, polythene.
Coping with rot
Rot attacks wood in which the moisture content has risen to around 20 or 25 per cent, either because the house structure is defective and water has penetrated structural timbers or, in the case of exposed woodwork, where surface protection has broken down and the wood has become saturated. Structural timbers are particularly prone to dry rot, which can seriously weaken them, while exterior timber is usually attacked by wet rot. In the former case a professional inspection is advised to gauge the extent of the trouble, since the fungus can affect masonry as well; treatment involves cutting out and replacing all infected timber, and spraying nearby timber and masonry with special chemicals to prevent reinfection.
In the case of wet rot, minor attacks can be cured by allowing the wood to dry out, and if necessary cutting out and patching affected areas with wood filler or new wood. The use of wood preservatives on all new work will help to prevent the incidence of wet rot, but the best protection of all is to ensure that exterior woodwork is painted or varnished on all surfaces and that joints are tight and sealed with filler, so that water cannot penetrate and start an attack.