Precast Kerb Comparison
What You Should Know About All Types of Precast Kerbs
Kerbs are essential infrastructural products. They serve a number of purposes:
- Kerbs retain the roadway edge to prevent erosion and loss of structural integrity.
- They act as a barrier or demarcation between road traffic and pedestrians.
- They provide a physical ‘barrier’ to prevent vehicles leaving the roadway.
- Kerbs form a channel along which surface water can be drained.
- Some kerbs are mountable in order to create easy vehicular access where required.
All reasonably made kerbs should last a lifetime.
Good quality kerbs are accurate in sizing, consistent in appearance and comply with SANS 927. The colour of aggregates and cement used in production generally determine the colour of kerbs. There might be slight variances in the colour of kerbs (in fact, any concrete).
Kerbs are infrastructural products, not pretty products. They become discoloured and damaged on site very quickly, due to the following:
Manufacturing Methods
- Dry mix pressed or “dry cast”.
- Wet mix pressed – water is sucked out of the concrete through filter paper.
- Wet cast, in steel moulds.
A Brief Comparison
Dry mix pressed
The positive:
- Accurate and consistent in size.
- Quick to manufacture – supplying large jobs reliably.
- Can be manufactured with features like a castle bottom and spacing nibs.
- Due to the above it is much quicker and cheaper to install.
- There are no quality concerns due to moulds warping and stretching etc.
- Much less prone to acid attack than the other methods.
The negative:
- It has a rougher surface texture than wet cast kerbs.
- All pressed kerbs have ridgeline caused by the manufacturing process.
Wet mix pressed
The positive:
• Quicker to manufacture than wet cast kerbs.
• More accurate in sizing than wet cast kerbs.
• No effect from mould warping.
• Not as prone to acid attack as wet cast kerbs.
The negative:
• “Pimple” texture on the face due to filter paper used.
• Brittle edges where water and cement get sucked out in the manufacturing process.
• All pressed kerbs have a ridgeline caused by the manufacturing process.
Wet Cast
The positive:
• Easy to set up manufacturing because capital cost is much less.
The negative:
• Inconsistency and great size variances.
• Surface imperfections like pinholes and warping are common.
• Greatly susceptible to acid attack because the surface cement paste is thin and comes off quickly.
• Very brittle edges because water and cement escape at these points.
• Control of concrete consistency is more difficult due to manual production processes.
