Jointing Sand Calculator

Sand needed = paved area × joint plan-area fraction × joint depth × sand density. The joint fraction depends on your paving unit size: for a grid of units measuring a × b (mm) with joint width w, fraction = 1 − ((a−w)/a) × ((b−w)/b), because joints run in both directions. Smaller units (block pavers) have far more joint length per m² than large slabs, so they use more sand.

For standard 200 × 100mm block pavers with 3mm joints filled to full 50mm depth, roughly 3.3 kg/m² — so a 20kg bag covers about 6 m² of new paving. Deeper 80mm blocks rise to about 5–6 kg/m². Re-sanding cleaned existing paving uses much less because joints are only partly empty.

Yes, 5–10% extra is recommended. Kiln-dried sand is swept in dry and a fair amount blows away or stays on the surface, and joints settle after compaction so they need topping up.

Polymeric sand contains a binding agent that hardens when wet, locking pavers in place and resisting weed growth and ant nests. It is more expensive than kiln-dried sand but much more durable. Joints generally need to be at least 3mm wide and 25mm deep for it to cure properly.

Make sure the paving and joints are bone dry. Tip kiln-dried sand over the surface and sweep it into the joints with a stiff broom, working diagonally across the paving. Vibrate or compact, then re-sweep and top up until joints are full and level. For polymeric sand, brush in, remove all excess from the surface, then activate with a fine mist of water following the product instructions.