Learn About Kerbs

Bosun is the only manufacturer in South Africa using the “dry cast” method to produce precast concrete kerbs. In Europe, this is the preferred method of manufacture and we firmly believe that kerbs produced according to this method are of consistent better quality than those produced by other means. Herewith a helpful list of short articles to consult when researching the purchase of kerbs, the installation of kerbs as well as when potential problems arise after installation.

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Dry Cast Kerbs versus Wet Cast Kerbs

Wet cast kerb was installed next to a dry cast kerb. Two years later the dry cast kerbs are darker, the surface doesn’t abrade as easily and withstands acid attack better in the long term. Wet cast kerbs are manufactured in the same way as cobbles. Dry cast kerbs are manufactured in the same way as interlocking pavers.

Bosun kerbs are designed consistently with high quality in mind, ensuring a durable and resilient form. Our kerbs, being manufactured out of concrete, are fire resistant; and due to their solid form, are robust in nature.

Bosun dry cast kerbs were used on the left-hand side of this traffic island. Wet cast kerbs were used on the right-hand side. It is clear to see that the dry cast kerbs are dimensionally more accurate than the wet cast kerbs.

Dry Cast

Wet Cast

SANS Specifications for Concrete Kerbs Explained

The South African National standard for precast concrete kerbs, edgings and channels SANS 927:2013:

Bosun kerbs adhere to SANS specifications and are all manufactured according to the required specifications and product guarantees are based on the same rules.
Kerbs are made up of high quality materials.
The kerbs will be free from cracks other than hairline cracks. They will also be free from visible twists and dents.
Kerbs dimensions stay within +3mm of length and straightness.
Kerbs comply with strength specifications.
Kerbs are sampled and tested in a lab.

Kerb Installation Guidelines

The guidelines below are largely based on SANS 1200MK, the official South African Standard for the installation of precast concrete kerbs.
As SANS 1200MK was last updated in 1983, we have also included key points from the British standard for the installation of precast concrete kerbs.

The following is stipulated in SANS 1200MK:

  • Trenches for kerbs and channels shall be excavated to the correct depth.
  • Bedding material is to be crushed stone, cinders, slag, sand or other approved porous material having a maximum particle size if 13,2mm.
  • This bedding material should be placed on a compacted subbase (90% of modified AASHTO.)
  • Units shall be laid with joints not exceeding 10mm.
  • 3:1 sand cement mix will be used to joint the kerbs. The ends of the units will be well moistened before jointing. Joints will be covered and kept moist for 40 hours after installation.
  • Provision shall be made for expansion joints at least every 20m.
  • Expansion joints will be filled with a suitable sealant.
  • After grouting the kerb joints, the kerbs shall be backed with concrete with a strength of 15MPa.
  • The backfill behind the kerbs needs to be compacted to 90% of modified AASHTO.

The British Standard stipulates:

  • The subbase should extend to behind the kerbs to be installed.
  • Kerbs should be installed on a concrete bed which is on top of the subbase mentioned above.
  • Kerbs should be backed by concrete and not only haunched with concrete behind their joints.

Bosun recommends the following:

As the British guidelines suggest, it is common practice in South Africa to use a concrete foundation for precast concrete kerbs. This is recommended by Bosun.

It is important to fill expansion joints with a suitable sealant in order to prevent bedding and jointing material of segmented paving behind the kerbs seeping out of empty expansion joints.

Precast kerbs are commonly installed in combination with cast in situ channels. Bosun recommends the use of precast channels which eliminates many issues caused by cast in situ channels.

However, if channels are cast in situ, precast kerbs should be covered in order to protect them against concrete splatter. It is also recommended to protect kerbs against asphalt splatter.

Kerb Installation Cross Section Detail

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Kerbs generally weigh in excess of 100kg per unit. Bosun actively promotes the use of specialist handling tools in order to protect workers on site.

These tools are available from www.cretesol.co.za

Kerb Innovation

Bosun manufactures a range of precast kerbs with innovative castellated bottoms and with spacer nibs. The patented Castle Bottom design ensures better adhesion in all directions, while the spacer nibs ensure even spacing between units. Click below to view more: