How to maintain garden paths and drives

Damaged paths and drives are dangerous as well as unsightly. Yet maintenance and a few simple repairs are usually all that are necessary to make them last a lifetime.

The most common materials used for paths and drives—concrete, tarmac and bricks—should last for years providing they have been properly laid and finished off. But even so, continuous use, frost and subsidence can all take their toll by causing surface damage. This is best put right before it becomes too extensive.

Concrete paths and drives

Structural defects in concrete can cause it to crack, chip easily or become uneven. The most common reasons for this are: an inadequate or unsuitable hardcore base which leads to subsidence, expansion of the concrete in warm weather which leads to buckling, an inadequate thickness of concrete, badly laid or poor quality concrete and badly laid or poor quality surface screed.

Not only do broken edges and cracks detract from the appearance of the path, drive and surroundings, they can also be dangerous. And if they are not repaired, the faults will spread, obliging you to break up and relay large sections. Prompt action saves both time and money.

Filling cracks

Providing there are no signs of serious subsidence, you can patch up cracks in paving concrete with a 1: 6 cement-sand mortar mix. To ensure a good bond with the original concrete, you also need a supply of PVA bonding agent, which you can buy from builders’ merchants.

To provide a good key for the mortar, chip the crack out to a width of about 25mm with a hammer and bolster. Be sure to wear goggles to protect your eyes from flying bits of masonry. Afterwards, brush away the debris with a wire brush and paint on a coat of the bonding agent.

Add a little more of the bonding agent as you make up the mortar, but remember that this means you will need less water in the mix. Force the mix well into the crack using a pointing trowel and smooth it level with a flat piece of wood or a wooden float. Where a crack extends to the edge of a path or drive, take particular care that the mortar does not fall away after application. You may find that a timber former helps to give the edge a clean finish.

Where cracks or chipping at the edge of the concrete are confined to a small area—possibly the result of lawn-mower damage—hack away the damaged material back to firm concrete and brush it out. Check that the base below is sound, tamping it down and adding a little more hardcore if necessary—you can use the old, chipped concrete for this.

Use a timber former to form the new edge, paint on some bonding agent, then fill the hole with mortar as above. Leave the repair for at least a week before treading on it.

Surface chips and flakes often appear in screeded concrete or in concrete which has been laid too wet. In the latter case, the flakes are due to laitance—a thin layer of watery cement and fine ballast—which forms on the surface of the concrete leaving a rough aggregate surface below.

If the damage is not too extensive, you can patch it with a 1: 5 mortar mix including a proprietary hardening additive. Chip away all the loose—or potentially loose—debris so that the repair mortar has a substantial hole in which to settle.

Where the screed shows signs of being too thin and badly laid, or where there is excessive laitance, you have no choice but to rescreed the entire area. Excessive laitance is a common fault in concrete laying and is mainly caused by over-trowelling with steel tools. When steel is applied to the surface of wet concrete it causes water to rise to the surface, bringing with it raw cement. It is this water-cement scum on the surface, which, when dry, becomes laitance.

Also remember that laitance means less cement in the concrete body, which of course means a weak concrete mix. Excessive laitance can be avoided by using wooden floats to level and solidify the concrete, as these keep the mixture well bound together.

Cracking and subsidence

If this becomes apparent, the most likely reasons are that the concrete is too thin or that there is something wrong with the hardcore base on which it has been laid.

The minimum recommended thicknesses for concrete are 75mm for paths and 100mm for drives, laid on a base of well-tamped hardcore. In the case of drives, it is preferable—especially on a light soil substrate—to reinforce the concrete with steel reinforcing mesh which is obtainable from builders’ merchants.

The mesh should be 100mm x 100mm formed from 6mm wire and should be set 40mm above the hardcore. If your concrete does not match up to this, the only permanent solution is to relay it. However, as a temporary measure, it is well worth filling in the cracks in order to stop any water from entering the concrete and cracking it still further.

Subsidence—likely wherever the concrete cracks and sinks—will probably be confined to a localized area. The only remedy is to hack away the subsiding material back to firm concrete and relay.

Once you have removed the old concrete, inspect the base carefully. It may be that no hardcore was used, the base was not properly tamped, or that the ground is indeed slipping. Less likely, but still possible, is that the original hardcore contained plaster or rotting waste which has eaten away at the cement in the concrete.

Unless you are confident that the ground is firm, it is a good idea to dig out the old base and make a new one with fresh hardcore. Use only clean brick, aggregate or old concrete for this. Hogging—waste sand from gravel pits—is ideal if you can get it, being easier to compact and level than ordinary broken brick.

When you come to lay the fresh concrete, coat the edges of the existing concrete with bonding solution and make sure there are no crumbling patches left.

Cracks due to expansion

Sure signs of this are when the concrete appears to have lifted slightly around the cracks. Although concrete shrinks when it is drying out, hot weather may later cause it to expand considerably. If there is no room for movement at the edges, it forces upwards, cracking in the process.

In addition to filling in the cracks, it is necessary to provide expansion joints to allow for future movement. Do this at the edges by chipping away about 25mm all round, especially if the path butts up against a wall, then cut another 25mm groove across the width of the affected area.

Fill the joints with strips of 13mm bitumen-impregnated insulation board, then pack any gaps with pitch or a 1:6 mortar mix. Finally trowel, the filling level with the surrounding area. Any further movement will be confined to the filled joints—which can be patched up easily.

Surface damage

Superficial surface damage caused by general wear and tear can often be patched with a proprietary surface sealer. These are available from builders’ merchants in polyurethane, epoxyresin and vinyl-based forms and are easy to apply—just follow the manufacturer’s instructions.

Before you apply a surface sealer the surface must be free of flakes, dust, vegetable growth, lichen and grease or oil. De-greasing agents are available from builders’ merchants, motor spares shops and some garages. Lichen must be scrubbed off with a stiff wire brush and the concrete should then be treated with a proprietary lichen inhibitor, also available from builders’ merchants.

Faded concrete and concrete slabs can be revived by washing off the dirt and then removing the surface layer of cement, which has usually decayed slightly. Use a dilute solution of hydrochloric acid—available from large builders’ merchants, and apply the liquid with a stiff brush, taking care not to contaminate nearby soil.

When the surface has stopped fizzing, hose the path down thoroughly with plenty of cold water. You must wear protective rubber gloves when using acid and protect your eyes with goggles. Keep children and pets away from the area you are treating.

Brick paths and drives

Only hard bricks should be used for drives and paths, the most suitable being purpose-made paving bricks. Such bricks are only half the thickness of ordinary building bricks, but their length and breadth are the same. Commonly known as paviours, they are rarely kept as stock by brick merchants and may have to be specially ordered to your requirements.

Ordinary household bricks are not noted for their resistance to wear when used for paths and drives: water enters cracks in their surface, expands in cold weather and eventually causes the bricks to break up completely. For safety’s sake it is a good idea to replace those bricks which have crumbled to the stage where they leave a hole.

Dig out the remains of the old brick carefully, taking care not to damage those around it. Bed in the replacement with a strong 1: 3 mortar mix, slightly on the wet side to allow for adjustment. If you find that the brick is out of level with the others, remove it and start again—do not try to force it, or it is likely to split.

Fill the mortar joints around the brick—together with any other joints which have crumbled—with the usual 1: 5 mortar mix. Maintaining the joints in good condition goes a long way towards stopping the bricks from breaking up and turning to dust.

Tarmac and asphalt

Drives and paths made from tarmac or asphalt, the latter containing a higher proportion of bitumen binder to aggregate, improve with age as the surface becomes more consolidated. But after a while the binder loses its adhesive properties, releasing bits of aggregate and causing the surface to break up.

If you catch it in time, you can treat this problem by applying an emulsion, or tack coat, of binder and fine grit. Both materials are available from builders’ merchants who will usually deliver them to your door. Be sure to quote the area you wish to cover when ordering.

Having swept the area clean, and clear of loose chippings, brush on the tack coat as evenly as possible. Shovel the grit on top of this, adding just enough to cover the tack coat and fill any depressions.

When the tack coat starts to harden, run over the area with a garden roller dampened with water to prevent the binder sticking to it. A week or so later, brush away any surplus grit.

Repairing the edges

The edges of tarmac and asphalt drives and paths are best lined with kerb stones to stop them crumbling. The procedure for mending the edges follows closely that for repairing concrete edging, except that in this case you need a supply of ready-mixed tarmac or asphalt.

Use a hammer and bolster to cut back the edge to firm material, forming a regular, straight-sided hole. Having brushed away the debris, and flattened and levelled the base, secure a timber former along the old edge and tap it down level with the surface of the existing tarmac. sure that it is firmly fixed.

Warm the ready-mixed tarmac according to the manufacturer’s instructions and shovel enough into the hole to protrude slightly above the surrounding surface—if you heat your spade beforehand, the tarmac will not stick to it. Wait until the mixture has started to harden, then roll it flat with the dampened roller. Remove the timber former when the tarmac has fully hardened.

If you do not have a roller, you can compress the tarmac using a special tool called a punner. Make this from a 150mm x 150mm piece of block-board nailed to a broom handle or other suitable length of timber.

Use the punner to press on the fresh tarmac, making sure that you cover the whole area. If small indentations are left between strokes, fill them with more tarmac and repeat.

Holes and damaged patches

Use a hammer and bolster to chip holes and damaged patches back to firm tarmac so that you are left with a larger, square or rectangular hole. Check that the base below the tarmac is firm and level, adjusting the height where necessary, then fill and roll as above.

Flagstone paths

Cracks in flagstone paths are rarely worth patching: it is better to replace the damaged stone. Take great care when you prise this away or you will damage those around it.

Inspect the base under the stone for signs of subsidence or inadequate hardcore and correct as necessary, bringing it up to the level of the hardcore under the other stones.

On top of this, lay a bed of strong, 1: 3 mortar and smooth it out as level as you can. Gently position the new stone, then check it for level with a straightedge. Make small adjustments by lightly tapping the stone with a piece of heavy, but soft, timber. Finally, fill in the surrounding joints with 1: 6 mortar.

Gravel drives

Normally the only problem with these is that hollows develop, leaving ‘bald patches’ of the base material. Rather than try to distribute the existing gravel, it is better to enlarge the hollow to form a completely clear patch then fill it with fresh gravel. Use a garden rake to blend the old and new gravel together.

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