Materials you'll need:

• Builders, sand
• Dry sponge
• Sand-cement mix
• Commercial bonding agent
• Sacking or plastic sheeting
• Timber plank
• Fine aggregate
• House bricks

Tools you'll need:

• Cold chisel
• Hammer
• Stiff brush
• Garden hose
• Wheelbarrow (for mixing)
• Trowel
• Timber float or 2 x 4 screed

As a path, driveway or step wears, cracks and holes often develop with time and traffic. If not fixed they can become dangerous, and holes in a driveway can be hard on your car tires. It is not enough, however, to just pour a dollop of new concrete into a hole or crack. That may work for a while but soon the patch will crumble at the edges and the repair will come loose. With care and the right preparation, this need not happen. Here's how to make effective, long lasting repairs in concrete.

Paths and driveways.

If a crack in a path or driveway is ignored it will soon widen and become a real danger. As more and more material works loose, the inner-edges of the crack are affected by changes in moisture and temperature so the crack grows at an alarming rate. Since fixing a small crack is far easier than a large one, the sooner you get around to it the better.

    1. It may seem strange that you repair a crack by first making it bigger, but this must be done to ensure the new concrete can grip the sides of the crack properly. The process is called undercutting. Use a cold chisel to widen the crack to at least 2cm wide, making it wider at the bottom of the crack than on the surface. Protect your eyes from flying concrete chips by wearing safety goggles, or simply push chisel through a plastic ice-cream container lid and position as close to bottom of chisel as possible to stop chips flying up.
    2. Now use a stiff brush to remove all the loose concrete and debris from the crack. Hose out to complete the clean-up.
    3. If the crack goes right through the concrete slab to the ground beneath, put a layer of builders' sand into the crack and tamp it down before adding the concrete.
    4. Remove any standing water from the crack by pushing a dry sponge into the crevice so it soaks up the water. The work needs to be damp but not running with water.
    5. Prepare a mix of cement, sand and water add some commercial bonding agent, following the directions on the product. Alternatively, coat the inside of the crack with a bonding agent. Now push the mix well into the crack with a trowel.
    6. After about 45 minutes, when the mix starts to set, level the patch with a screed made of an off-cut of 2 x 4 soaked in water.
    7. For a strong joint, cover the repair with a piece of wet sacking or plastic sheeting and allowing to cure for four to six days.

Patching holes.

A lot of the rules for patching cracks apply to filling holes.
    1. First, you must clean out the cavity of all the loose concrete. Once you have chipped loose all the fragments, hose out the cavity. The cleaner it is, the better your chances of obtaining a patch that will stay put for a long time.
    2. Remove any standing water from the cavity using the dry sponge as described above.
    3. You can mix your own concrete but it is probably quicker and just as economical to use a bag of ready-mixed concrete. The mix should be thoroughly blended to ensure all the sand and aggregate is coated with grey concrete, then add water as directed on the pack. Remember that too much water weakens the mixture.
    4. As well as the concrete you will need a quantity of commercial bonding agent which locks the patch into position permanently bonding the new concrete to the old. Follow the instructions on the product. It is usually brushed onto the inside of the cavity or added to the mixture.
    5. Pour the mix into the hole and work it into the cavity with a trowel. Level the patch with a length of wet 2 x 4 timber stretched across the hole.
    6. When the surface sheen disappears from the concrete, smooth the patch with a metal or wooden float. Pull a stiff bristle broom across the surface if you want to make it non-slip.
    7. When the surface sheen disappears again, cover the patch with wet sacking or plastic sheeting. Each day until the concrete cures (6 days is ideal), remove the cover, spray the surface with the hose set on "mist," and cover the patch again. This ensures the concrete hardens and cures to a really durable surface.

Steps and edges.

Steps and edges have one thing in common: they are easily damaged and often become chipped and unsightly. A badly chipped step can also be dangerous so repair them right away.

Here’s how.

If the whole edge is crumbling, however, more work is needed to restore it.

    1. Undercut the edge using a cold chisel and hammer to shape a V-cut back into the good concrete.
    2. Remove all the debris from the hole with a stiff brush and hose out the remainder.
    3. Make a timber support as wide as the step and high enough to be level with the new edge. Hold it in place against the riser with a couple of house bricks. The ends can be supported with timber.
    4. Prepare some ready mixed sand and cement or a 1:3 cement-sand mix, ensuring that all the sand is well blended with cement. Add enough water to make a stiff but workable mixture. Ready-mix will have directions on the product. If necessary add a fine aggregate for strength.
    5. Apply commercial bonding agent to the edge of the step as directed on the product and add some to the cement for extra adhesion.
    6. Pack the concrete mix into place with a trowel, tamping down well to avoid leaving any air spaces in the crack. Finish the patch level with the step using a trowel or wooden float. Ensure the texture of the patch matches the surrounding step.
    7. Cover the repair with damp sacking or plastic sheeting and spray with water each day for five days, until the repair has thoroughly cured. The timber can be removed after a day or so, but if left in place for the whole period, it will protect the patch more effectively.