Bedding material for paving blocks and bricks
The incorrect selection of bedding sand is a major cause of site failures.
In simple language – well-draining river sand containing no clay and very little fines should be used for bedding.
The most important considerations for bedding sand is:
- Bedding material must drain well. Good drainage of bedding material is crucial for any paving installation.
Moisture trapped in the bedding material could cause black attack and other discolouration. Furthermore, when the bedding layer of paving becomes saturated with water, it will start pumping through paver joints, removing grouting material in the process.
- Bedding material should not contain any particles larger than 9.52mm in size. Large particles in the sand will cause point loads, which will cause pavers to break.
- Bedding sand should be moist when bedding pavers (not saturated with water, just moist), the sand should contain 4-8% moisture.
The sand bed must be laid slightly in advance of the placement of the units but only to the extent that the particular area of paving can be completed on the same day. With the sun baking down, it should be limited to a few hours at a time and its moisture content should be continuously assessed on site. When bedding sand becomes dry, it should be raked back into a heap, moistened and spread out again.
Dry bedding sand will not allow pavers to “bed in” when compacted, which will cause an uneven paved surface with many high and low pavers.
- Bedding sand should be 25-35mm in its compacted state. To achieve this, it should be screeded to a thickness of 30-40mm, which will in turn compact to the correct thickness once pavers are installed.
Insufficient bedding material will cause an uneven paved area with pavers breaking.
- Bedding sand should be screeded with a straight edge (straight plank or similar), using rails in order to achieve the correct, even thickness.
- If you install pavers according to the flexible method, do not mix cement with bedding sand, unless specified by an engineer.
Bedding material as specified by SANS1200MJ