There can be inherent potential problems with concrete finishes, some that can be avoided or minimised and some that cannot. You need to be aware of these limitations and potential problems as they may not be covered under the Consumer Guarantees Act or our terms of trade.
Waikato Concrete Ltd will not be liable in the event the below-described issues occur arising from:
- Factors beyond our reasonable control, or
- You not following our advice and recommendations, including as to concrete care and maintenance.
Finishing
The finishing process can only begin when the concrete has stiffened sufficiently and the bleed water has evaporated from the surface. The timing of this depends on both the weather and the concrete temperature.
Curing
Concrete should be protected from early loss of moisture. This can cause shrinkage and cracking. A good curing environment should exist immediately after finishing and for up to seven days later.
Plastic Shrinkage Cracks
Plastic shrinkage cracks may form in the surface of the concrete before it has set (or in a “plastic” state). This may not become visible until some time later.
Factors which lead to plastic cracking due to high evaporation rate:
- Sunny or windy days.
- Low humidity.
- Exposed sites.
This can be addressed by covering the concrete with polythene or a membrane cure immediately after finishing.
Colour Variations
There will always be a natural variation in colour, texture and appearance due to concrete being a natural material.
Be aware that:
- Areas in shade, the time of day, and concrete poured in stages on different days can affect the final colour.
- Accelerators can cause the concrete to produce a variable colour.
- Coloured concrete may require an acid wash to remove or reduce efflorescence (white minerals) from the surface. This process needs to be carried out by an appropriately experienced concrete contractor.
When sealing concrete it is advisable to:
- Not seal when the concrete temperature is below 12 degrees or when it is damp (moisture will make the sealer go ‘milky’).
- Leave a minimum of 28 days from placing until concrete is sealed.
How to minimise colour variations and patchiness:
Architectural and coloured concretes are prone to colour variations, fading of colour and other staining or patchiness issues. These are sometimes variously described as efflorescence, staining, pinto or burnishing stains. Some of these issues can arise notwithstanding that the concreting has been carried out with all reasonable care and in accordance with industry standards. To the extent that any colour variations and other issues are within “standard tolerances” and are not within our reasonable control (ie. have not arisen from defects in works or materials), we will not be liable for them.
The final colour of a concrete surface may be influenced partly by the water content of the freshly placed concrete (including weather conditions at the time of the placement and shading on site) and partly by a successful curing process and the finishing or texture of the top surface.