Joint sand is the material used to fill the gaps between interlocking pavers or bricks in hardscaping projects. The sand stabilizes the pavers by locking them into place and preventing movement. It also helps to prevent weeds from growing between the pavers and reduces water penetration. After the pavers are installed, joint sand is typically swept into the joints and compacted, creating a firm and stable surface. Polymeric sand, a type of joint sand that hardens when wet, is often used for added durability.