Advanced options
Trade rule of thumb: about 1 tonne of building sand and 6-7 bags of cement lays 1,000 bricks (blocks cover more wall per unit but take bigger joints, needing about 40% more mortar per unit laid). Standard 10mm joints, 5:1 building sand to cement with plasticiser; use stronger mixes below DPC and for exposed work.
What The Mortar Calculator Works Out
- Building sand: the bricklayer's planning rule that a tonne of building sand lays about 1,000 standard bricks at 10mm joints, so 500 bricks wants half a tonne. Blocks cover six times the wall per unit but drink roughly 40% more mortar each through their bigger bed joints, so the figure is 1.4 tonnes per 1,000 blocks.
- Cement: six to seven 25 kg bags per 1,000 bricks (nine per 1,000 blocks) at the usual 5:1 soft sand to cement mix with plasticiser for workability, mixed in small batches as the day goes. Mortar stays usable about two hours, less in heat, and must never be re-tempered with water once stiffening.
- Coverage check: 60 bricks or 10 blocks per m2 of single-skin wall converts the count back into wall area, a sanity check against the drawing.
- Work from wall area (advanced): enter the wall area instead and the calculator derives the brick or block count at 60 or 10 per m2 single skin. Double the area for a solid one-brick wall; cavity walls are two single skins.
- Mix (advanced): rescales the cement for the mix designation while the sand stays the same. General work above the damp course runs at 5:1; below ground, retaining work, copings and chimneys step stronger to 4:1 or 3:1, and soft old brick wants 6:1 or lime entirely. For anything structural, the mix on the drawing wins over any rule of thumb.
- Wastage (advanced): add 10% to 15% for droppings, mix left over at the end of the day and uneven joints; more for inexperienced hands.
- Sand bulk bags and cost (advanced): sand is sold in bulk bags of about 850 kg at roughly GBP 50 to GBP 75 each, cement at GBP 6 to GBP 9 a bag. The mix table shows cement and cost at every designation so you can see what a stronger mix really adds (usually a bag or two).
- Mortar volume and plasticiser (advanced): the mixed mortar at about 2,000 kg per m3, expressed in drum-mixer loads, and a plasticiser allowance of about 0.2 litres per bag of cement. Ready-mixed tub and silo mortar cost more per brick and buy colour consistency; for coloured work, mix from one measured recipe.