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In the building trade, two types of sand are prevalent; these are known as building, or soft sand, and grit, or sharp sand. The best choice of sand is determined by the proposed usage of the material. Soft sand generally creates fine mortars, either for rendering a constructed surface or jointing bricks and blocks. Conversely, sharp sand is primarily a bedding material, laid as a base for paving.
Sharp sand is constituted from rock grains ranging in size up to 2.0 millimeters (0.08 inches) in diameter. The particle size ranges used in different mixes result in a variety of grades being available. These grades are created through the use of sieves with precise gap dimensions. The material retained within the sieve once the sand has passed through possesses a minimum diameter as determined by the size of the sieve.
There are a variety of purposes for which sharp sand can be utilized, including bedding, pointing, and as a drainage media. By mixing sharp sand through compost or stiff soils, water transition can be improved due to the open structure and coarseness of the sand. When used for bedding, the best sharp sand grading is a coarser one than that used for jointing of block paving. Generally, bedding sand should feature around 50 percent passing through a 0.5 millimeter (0.02 inch) sieve; this compares to 100 percent passing a 0.5 millimeter sieve for jointing sand.
The final application of the paving should also be considered when deciding what grading of sharp sand to use for bedding. Sand grades with lower percentages of fine particles are generally more reliable as a bedding material for heavy-duty applications. It should also be considered that naturally rounded sands will settle less under loading than the more angular sands. This is because rounded sand compacts more readily on placement rather than under loading, as is the case with angular sand where the sharp edges can shear off, increasing the percentage of fine particles present and resulting in the gradual settlement of the bedding layer.
For common usage, a general grit or sharp sand is sufficient for the majority of domestic applications. Attention to the individual grading and composition of bedding sand is only really required when major industrial or commercial applications such as airport taxiways, freight yards, and city center roadways are being considered. The sand used for jointing block paving should have low clay content and contain a greater ratio of fine particles than bedding sand. These fine particles increase the level of friction under load and help to prevent lateral movement in the block paving.
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