Building sand is made up of fine to medium grained particles, between 0.2 mm and 0.7 mm in size, which are rounded and uniform in size. When building sand is mixed with cement and water, it makes a workable mortar mix which is sticky, capable of being squeezed into gaps and supporting the weight of several bricks or blocks but does not flow. A fairly uniform colour is also important for visual appearances. Sand worked at sand and gravel quarries is a mix of coarse sized sand up to 3 mm in size and is usually angular in shape which means it is unsuitable for mortar mixes.