Is it difficult to repair concrete?

If concrete is mixed, placed and cured correctly there should be no need for repairs which are difficult to execute. Listed below are ways in which concrete can be resurfaced and slippery concrete surfaces can be rectified.

Resurfacing Finished Concrete

This can be achieved by the application of a topping which is suited to both old or new concrete. Surfaces must be completely clean - free of dirt, grease and dust. Good preparation will contribute greatly towards a satisfactory result.

Resurfacing methods available:

Levelling Compounds

Available from most builders' hardware suppliers, levelling compounds would typically be mixed with water then screeded and trowelled onto the concrete surface. Beware that some compounds may not be suited to outside use. Seek advice from a builders' hardware supplier about the most suitable product for the particular application. Observe product manufacturer's instructions.

Unbonded Topping

Unbonded toppings would typically be used to refurbish an existing pavement. The concrete mix comprises 1 part cement: 2 parts sand: 3 parts coarse aggregate (10 mm nominal maximum size). Cover the surface with a plastic sheet to give a definite separation from the base concrete. Fix formwork in place to new predetermined levels, allowing for a minimum of 75 mm of topping.

If topping is to be thicker than 50 mm, reinforcement should be used. Place reinforcement such as F42 fabric or similar. If you are topping a large area, it should be divided into bays limited to 14m with a length-to-width ratio of 1 :1.5. Place, finish and cure concrete as described previously.

Note: If topping exceeds 75 mm (thickness) it may be regarded as a new concrete slab.

Rectifying Slippery Concrete Surfaces

Smooth concrete surfaces that have become slippery may be rectified either by using a highpressure water blaster or by acid etching the concrete surface

If you use a high-pressure water blaster, the equipment hired must be capable of delivering pressure of between 1000 and 1200 psi to achieve surface texturing. It is recommended you seal the clean concrete surface (once dry) to minimise dirt and grime from later penetrating it.

Acid etching will require care in both application and handling. Should you wish to undertake the acid-etching process, it is recommended you obtain a copy of the Cement and Concrete Association of Australia's Concrete Information - Treatment for Slippery Concrete Surfaces.

Controlling Cracks in Concrete

Why does concrete crack? How do I control it?

Concrete cracks typically result from failure to cure the concrete properly. However, the cause may also be the result of poor site preparation and attention to detail in mixing, placing and finishing concrete with the inclusion of appropriate control joints.

The prevailing weather conditions may also contribute to cracking, with the risk most likely on warm days, dry days with low humidity and/or windy days.

To control the incidence of concrete cracks, the following advice is offered:

1. Prepare the site properly, including where control joints will be. Ensure correct placement of steel reinforcement if used. Spread a 10-mm base layer of sand or fine gravel over the formed area to act as a slip-joint between the ground and the concrete. Ensure that formwork is level, firm and properly fixed in place.

2. If mixing concrete on site, mix the concrete correctly. Use a container, not a shovel, to measure each part of materials used in the mix. Add only enough water to obtain an even, workable mix.

3. Place the concrete carefully.

4. Ensure thorough compaction of the concrete during placement.

5. Start early. Avoid concreting in the middle of the day. Make sure there are sufficient able-bodied helpers to assist in placing, compacting, and finishing the concrete. Work at a steady pace until the entire job is complete.

6. Avoid, if possible, executing major household concreting projects on warm sunny days, dry days with low humidity, or cold and/or windy days (see How does weather affect concrete and concrete operations). Heed the prevailing weather conditions: if the weather is forecast to be hot, dry or windy - dampen the subgrade (ground) and formwork before placing the concrete. Make sure the work is adequately prepared because there will be less time to place, compact, finish and cure the concrete in weather conditions described above.

7. The concrete MUST be finished correctly - from initial screeding to final finish; including properly positioned and constructed control joints.

8. THE CONCRETE MUST BE CURED.