Sand comes in five grades or sizes — Very Fine, Fine, Medium, Coarse and Very Coarse. Sand is an engineered aggregate, just like gravel. In fact, the only real difference between sand and gravel is size. Sand is rock particles from a sixteenth of a millimeter up to two millimeters long, while gravel is rock particles from two to sixty-four millimeters long (2.5 inches). Sand particles excavated from natural sources are mostly rounded and smooth from natural erosion. Sand particles that come from gravel crushing are sharp and angular, and “lock up” against gravel better than rounded sand.
Dirt, clay silt and rock dust is sometimes added or allowed to remain in certain sand mixes, but as a rule sand is thoroughly washed and screened to create an extremely clean aggregate of a uniform size. The finer grades are typically used in making industrial products, while the coarser grades are more often used for construction and landscaping. Sand is mostly silica, an inert and extremely hard mineral, so it is a super tough and reliable product. Used correctly, it’s going to stay where you place it and do its job indefinitely.
Sand has a special quality of filling the empty spaces between gravel and binders like cement, asphalt or epoxies, adding strength and bulk to the mix. It’s the sand that adds high compression strength to concrete. Gravel and cement alone makes a crumbly mess. Gravel, sand and cement makes skyscrapers and bridges that last for decades.
Landscaping sand is often chosen for its color, such as extra-white sand for golf course bunkers, beaches, volleyball courts, and playgrounds. Red mortar sand is favored for concrete and for the mortar in masonry walls both for its strength and the uniform gray color it provides. A topsand dressing on a lawn can help loosen and aerate clay soil. Particular grades of sand (like C33 or C10) are often specified in the building code for concrete construction and septic tank systems. It’s also a good choice for setting pavers.