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Grass Block Installation Guideline

These guidelines are intended to offer simple advice on the installation of Bosun Grass Blocks. Much of the information contained in this document was extracted from SANS 1200MJ, the official South African standard for concrete paving installation.

Bosun cannot guarantee that the information in this document is 100% correct for any individual project and therefore can’t accept any responsibility for errors or problems  encountered by anyone who uses the information in this document. Bosun strongly recommend that you obtain professional, on-site advice by an engineer, as every paving project is unique with its own unique problems.

We consider this document as work in progress. Please share any further advice with your Bosun representative in order for us to improve these guidelines where possible.

The Bosun Grass Block with its honeycomb cavities is designed to facilitate the growth of grass within a supporting concrete matrix, allowing grass to be mowed in the conventional manner. Because of its design, the Bosun Grass Block, like any other grass block is not recommended for heavy duty industrial applications.

CONCEPTUALLY THERE ARE TWO APPLICATIONS FOR BOSUN GRASS BLOCKS:

  • A paved surface planted with grass, designed primarily for its permeability.
  • A paved surface planted with grass, using standard paving construction methods.

1. CUSTOM ENGINEERED WATER PERMEABLE SYSTEM

  • The Bosun Grass Block, is a permeable form of paving for areas where the stability of paving is needed, but the function and aesthetics of grass is desirable. The Grass Block system allows some storm water to infiltrate through the grass cells, decreasing the volume of runoff that leaves the site.
  • For a system where permeability is of critical importance, it is recommended to consult an engineer about the design of suitable, permeable layer works.

2. STANDARD PAVING CONSTRUCTION DESIGN

BASE COURSE PREPARATION

The base-course is the foundation for thee Grass Blocks.

  • Bosun recommends excavation to the depth of 240mm. (Bear in mind that Grass Blocks are thicker than normal pavers and therefore require deeper excavation). This will allow for a 100mm thick sub base , 100mm thick Grass Blocks and 40mm bedding material. In some instances, the soil found on site could serve as base course but it carries unnecessary risk as the material recommended as base course is cheap and easy to obtain.
  • Bosun recommends a 100mm thick base course to be constructed with G5 material.
  • More important is that the base course should be compacted with a roller or heavy plate compactor at least.
  • The compacted surface should be tight or close knit to prevent downward migration of bedding courses material.
  • An insufficiently prepared base course will cause any paving installation to fail in the long term.

BEDDING COURSE

  • The bedding course is the layer that the Grass Blocks rest on.
  • Well-graded, washed river sand is recommended as a bedding course material for Grass Blocks.
  • It is essential for bedding sand to be graded to the following specifications as per SANS 1200MJ and it may contain no foreign objects:

 

Nominal Sieve size (mm)Passing
9,52

4,75

2,36

1.18

0,600

0,300

0,150

0.075

100

95-100

80-100

50-85

25-60

10-30

5-15

0-10

  • The uncompacted bedding course should be 40mm thick.
  • Carefully screed (level) the bedding course with a straight edge.
  • Do not use topsoil or compost as bedding course even if grass will be planted in the blocks.
  • Bedding sand must be moist when the grass blocks are packed.
  • (According to SANS 1200MJ only enough bedding sand should be spread out for one days’s installation at the most. (If more bedding sand is spread out…it will become too dry.)
  • A well prepared, moist bedding course is a critical aspect of the installation of Grass Blocks. Apart from determining the accuracy of the installation, Grass Blocks will eventually fail if the bedding course was not sufficiently prepared.

EDGE RESTRAINTS

Restrain the perimeter of the laid Grass Blocks to prevent the washing out of the bedding sand and grout (this will cause subsidence of Grass Blocks on the edge and could result in movement of the blocks).

The best edge restraints will always be Kerbs but pavers laid in concrete could also be an option.

HANDLING OF PRODUCTS

To minimise damage to Grass Blocks during transport:

  • Transport in packs. Place packs as close as possible to the laying surface to prevent excessive handling.
  • Carry Blocks by hand to the laying area.
  • Blocks could also be transported in specially prepared wheelbarrows and packed / unpacked individually by hand. Wheelbarrows should have a padding lining and even between layers and blocks, similar to the thick fabric used by moving contractors.

SETTING OUT

Ensuring that your pattern stays aligned:

  • Use taut setting out lines, this is a grid of string or nylon lines spaced at exact intervals.
  • Constantly re-check your lines in all directions while installing the pavers as it is very difficult & time consuming to straighten at a later stage.

LAYING PATTERNS

The Bosun Grass Block can be installed in two laying patterns.

  • A Stack bond pattern where blocks are laid directly next to each other in a grid, similar to common tiles.
  • A Stretcher bond pattern where Grass Blocks overlap. Ensure that the honeycomb pattern stay aligned by carefully matching the straight edges with each other. (Recommended)

CUTTING

If necessary, Grass Blocks can be cut with an angle grinder using a diamond blade. Use the ridges on the blocks as guidelines where possible.

3. LAYING OF GRASS BLOCKS (APPLICABLE TO BOTH METHODS OF BASE PREPARATION.)

Basics

  • Pack the blocks and tap them down with a heavy rubber or special paving mallet. (Available to purchase from Bosun.)
  • In our experience, the greatest issues around this product are that this product must preferably be laid FLAT. If it is laid in curves, especially concave in nature, spalling could occur.
  • Spacers on the blocks will allow for consistent spacing between blocks.
  • Concrete is brittle. Consequently, expect up to 5% of the product to have small chips when delivered. Chipped products should be used for cutting where possible. It is imperative that the home owner, quantity surveyor and/or contractor allow for wastage of 5% in order to replace blocks that are chipped or damaged through handling during the laying process.

COMPACTING OF PAVING

It is recommended that newly laid Grass Blocks be compacted by:

  • A plate compactor with rubber mallet.
  • Ensure bedding sand is moist, yet not saturated with water when compacting at this stage.

JOINT FILLING

  • Riversand is used as jointing and filler material in the installation of Grass Blocks.
  • Sweep the riversand over the paved area in order to fill the voids and gaps between Grass Blocks.
  • Grass seeds and fertiliser could be mixed with riversand.
  • Compact the paved area again after filling the joints and voids and sweep additional sand onto the area if required.
  • Compost and lawn dressing are not recommended as joint filling but could be used to fill the upper part of the voids.

GENERAL

  • Creeping grasses like Kikuyu and LM are recommended to plant in Grass Blocks.
  • Tufts of non-creeping grass could be used when it is required to maintain a grid pattern. Consult a horticulturist for grass types suitable for this purpose in your climate.

 

Contact Us

Head Office
Cnr Cresset and Musket Roads
Midrand Industrial Park
Phone: 011 310 1176
Email: info@bosun.co.za