Step 1: FOOTING
Dig out trench approx. 200mm deep. The trench should be 60mm wide. Place and
well compact 100mm to 200mm of fine crushed rock (gravel). This base thickness
depends on the wall height e.g. 150mm thick for 1 metre high, 200mm thick for 1.5
metre high and over.
Step 2: SAND BED
Spread 25mm of sharp sand over the compacted base. This should be in a straight
line checked with a level. If the wall tapers, run a string line at the desired finish level,then gauge down at multiples of 180mm.
Step 3: FIRST COURSE
The first block course is now bedded into the sand bed. The use of a level and string is recommended to ensure that the first course is layed correctly. Make sure at least 100mm of the first block course is buried below the finish ground level with grave well compacted along the front of the blocks to stabilise.
Step 4: DRAINAGE & BACKFILL
Where an agpipe or strip drain is used, place behind base of first course. Backfil
behind the blocks using a clean free draining material (e.g. blue metal). Allow
300mm for walls over 1 metre. Now compact backfill material thoroughly to remove
all voids. If backfill is needed behind the drainage area, existing site soils may beused. (Do not use heavy clay).