Repairing Brick Walls
Brightening the brickwork can give a new lease of life to the appearance of the home. It is, however, also important to be able to patch up or to replace damaged bricks, cure flaws and deterioration to bricks, joints and surfaces and to recognise the problems of settlement, as well as the lesser one of shrinkage.
Brickwork may occasionally need smartening up. This may mean no more than cleaning it down with a stiff broom and clean water. Mould or lichen can be removed with a mixture of one part of household bleach to four parts of clean water. Do not use detergent, as this may affect the face work of the brick. Difficult patches of dirt can be brushed down with a wire brush. Avoid rubbing too hard, however, as this may again damage the brick face.
Dull and faded brickwork can be brightened by one of the brick dyes. These lighten after a time and need renewing periodically.
Efflorescence is a discolouration of white powder or feathery crystals, similar to damp salt, on the face of new brickwork or freshly plastered walls.
It forms because rainwater or water used in building a house soaks the brickwork and dissolves any soluble salts in it. The water evaporates, drawing the salt to the surface.
This does not damage brickwork but is unattractive. The walls can be brushed off periodically with a stiff-bristled broom. If you use a wire brush, avoid damaging bricks and pointing.
A neutralising liquid can be applied to remove efflorescence. Using a 100mm brush, two or three coats of a proprietary preparation should be used, allowing about 15 minutes between applications.
Redecorating on interior walls can usually take place about a day after treatment.
You cannot wash off efflorescence with tap water, since this usually contains chemicals which accelerate reappearance of salts.
Surrounding vegetation may also stain brickwork. First find the cause and remedy it, and then clean the brickwork with a stiff broom. It is wise to apply a coat of colourless fungicide. The wall should be treated in dry weather, so that the solution is not washed away by rain.
Rust is another discolouration which may appear on brickwork joints or around ironwork embedded in brickwork. Brickwork can flake and crack as a result of rust, so mortar around ironwork should be raked out. Clean the metal thoroughly and prime it. You may need to use a rust-neutralising agent on the metal.
Rust in brick jointing occurs as a result of ironstone in the sand. The mortar will have to be raked out and repointed.
Brick is porous and takes in moisture in wet weather which evaporates when the weather is dry. On very porous bricks, water may accumulate inside and freeze. Ice expands and may cause the brick to crumble or ‘spall’ at the edges. The brick then ceases to offer resistance to the weather and should be replaced.
Use a club hammer and bolster to remove damaged bricks, but protect your eyes by wearing safety glasses. Cut back till you reach solid brick. Remove loose material with a wire brush and then cut back the mortar joints with a narrow cold chisel.
A matching half brick can be used to replace the damaged portion. This is called a queen closer-that is a brick cut in half along its length. You can cut a queen closer with a bolster and club hammer, working steadily around the brick until it comes apart into two halves.
Either cut the queen closer slightly undersize, or cut back to slightly more than half a brick. This allows a sufficient bed of mortar for the brick to fit flush with the existing bricks. Apply a bond of PVAto both faces, and mortar in place using a 1:3 mortar mix, plus a little PVA additive. Point finally once bricks have set.
Sometimes you may have to remove entire bricks. This is done by removing the pointing around the brick and using a narrow cold chisel to dislodge the brick.
You may also have to break out an old brick in sections in order to remove other bricks more easily.
Damaged brick at ground level or below should be removed after first being exposed by raking the soil clear.
It is also worthwhile treating a wall with a water repellent. This will ensure, in the case of porous bricks, that frost does not damage the brickwork again.
Once you have made good any damage, form a thin ‘apron’ of rendering about 150mm high along the front of the wall. Add a waterproofing liquid or powder to the mortar or a water repellent to the rendering mix.
Before repointing badly deteriorated joints, lay a sheet of polythene down to collect mortar droppings. A plugging chisel and a club hammer are used to clear out old mortar from about lm2 of wall at a time. First clear vertical joints and then horizontal ones. Clear them to a depth of about 15mm, for any deeper may damage the wall.
Brush down the joints to remove dust and old mortar, and soak the brickwork, so that it does not absorb moisture from the new mortar.
Only mix up enough mortar for about two hours’ work. Use a hawk, and first practise picking up mortar with a smooth upward sweep on the back of the trowel from the mix.
Make sure that new joints match the old. Weather-struck joints give maximum protection from damp and are advisable on chimneys and house walls.
With rough-textured bricks, recessed joints are attractive, but flush or rubbed joints look better with smooth-surfaced bricks.
With the weather-struck joint, a sloped surface allows rain to run off. The horizontal joint is recessed beneath the top brick and overhangs slightly the lower.
Push mortar into the joints, first into the uprights and then the horizontals, the top and then the bottom.
Form the slope on weather-struck joints as you go. With other joints, leave the mortar flush with the bricks. Weather-struck joints are trimmed at the horizontal joints with a pointing trowel.
Slope vertical joints to one side, matching the horizontal with the trowel. Use a small trowel or a ‘Frenchman’, a tool to cut off excess mortar at the bottom of the horizontal joints, in conjunction with a straight edge.
The straight edge acts as a guide while you run the Frenchman along with the angled tip pointing downwards. Once the mortar has set, brush off the area you have been working on. Repeat the process over the next square metre of working area.
To form a flush joint, let the mortar become semi-stiff and rub a piece of sacking along the joint in one direction to flush this with the brickwork. Brush off when dry.
A recessed joint is formed with a piece of metal with a pointed curved end. This can be made from a piece of metal bucket handle, using the inside bend to strike the joint. Use the pointing tool to scrape mortar from both vertical and horizontal joints to a depth of around 6mm. Rub down the joint gently with a piece of wood so that the surface is smooth and water-resistant.
When repointing, you can add a vegetable dye or proprietary colourant to produce a matching or decorative effect. The colour will, however, be mutated by the texture of ordinary sand, so white sand should be used.
10. November 2011 by admin
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