The Mortar That Goes With The Bricks: Cement And Sand For The Same Wall

The Day The Mixer Stopped At Noon

The wall in this article, 3 m by 3 m at 200 mm thick with its 900 bricks, needs about 0.41 cubic meters of wet mortar, which becomes 3.1 bags of cement and 0.43 cubic meters of sand at a 1:4 mix. Nobody at my relative's house had done that sum. The bricks had been counted twice, argued over, and ordered with care. The mortar had been estimated the way mortar usually is, by glancing at the stack and naming a number of bags. At midday the bags ran out with the wall at half height, the mixer stopped, and six men stood in the sun while a rickshaw went for cement at retail price. That evening I rebuilt the materials list from the wall itself, using the volume balance this article teaches. The list took eleven minutes. The rickshaw had taken two hours. Nobody forgets the bricks on an order; everybody forgets that a fifth of the wall is mortar, until the mixer stops at noon.

Where The Mortar Hides In A Finished Wall

A finished wall is two materials wearing one face. Take one cubic meter of standard brickwork. The bricks inside it occupy 500 multiplied by the volume of one brick, 190 by 90 by 90 mm, which is 0.7695 cubic meters. Everything else in that cubic meter is mortar: 0.2305 cubic meters of it, sitting in the 10 mm joints between every brick. About a fifth of the wall, hidden in plain sight. The bricks for wall calculator prints this mortar figure beside the brick count for exactly this reason: the two materials are one volume, split two ways, and an estimate that covers one half and guesses the other is half an estimate.

Count the bricks and you have counted three quarters of the wall. The last quarter arrives in bags and in heaps of sand, and it stops the mixer when it runs out.

The balance runs backward just as cleanly. A wall of known volume gives up its mortar volume the moment you subtract the bricks. For the 3 by 3 m wall above, the wall volume is 1.8 cubic meters, the 900 bricks inside occupy 1.385 cubic meters, and the difference, 0.41 cubic meters, is the wet mortar that the mixer actually placed. Wet, though, is the word that trips the shopping list, because nobody buys wet mortar. You buy dry cement and dry sand, and dry material refuses to keep the same volume.

Wet Mortar Is A Liar: The Dry Volume Step

Dry cement and dry sand are full of air. Sand grains rest against each other with gaps between them, and cement powder is mostly trapped air by volume. Add water, mix, and compact the blend into a joint, and the volume settles down to less than the heaps you started with. Standard rate analysis handles the gap with one factor: dry volume equals wet volume multiplied by 1.30. The 0.41 cubic meters of wet mortar in this wall therefore starts life as 0.54 cubic meters of dry material. Skip this step and the order comes up short by nearly a third, which is a precise description of what happened at the mixer that noon. The joint article in this series, on Why The Mortar Joint Decides Your Brick Count, covers the other half of the same ten millimeters: what the joint does to the brick side of the balance.

Two Mixes, Two Shopping Lists

A mortar mix ratio splits the dry volume between cement and sand. At 1:4, one part in five is cement; at 1:6, one part in seven. Cement is priced by the 50 kg bag, and estimating converts its volume to weight at 1,440 kg per cubic meter, the standard density behind bag counts. The table splits one cubic meter of finished brickwork both ways, then prices the worked wall from the sections above.

Mortar materials per cubic meter of brickwork, and for the 900 brick wall:

One translation remains before the list can go to a shop. Cement sells by the bag everywhere, but sand sells by the cubic foot, by the trolley, or by the truck, depending on the city. The conversion is one multiplication: a cubic meter holds 35.315 cubic feet. The 0.43 cubic meters for this wall is therefore about 15.2 cubic feet of sand, and the per-meter figure of 0.24 cubic meters is about 8.5 cubic feet. Quote the sand both ways when you order, in cubic meters from the calculation and in cubic feet for the supplier, and measure the trolley bed when it arrives: length times width times the height of the heap, leveled, is the volume you paid for, and heaps have a way of shrinking between the yard and your gate.

Read the sand column with care, because it surprises most buyers: the leaner mix needs slightly more sand, not less. The total dry volume is fixed by the wall; a leaner mix simply fills more of it with sand and less with cement. The saving at 1:6 is a cement saving, about one bag in three on this wall, and it is bought with strength the wall may or may not need. Richer mixes belong on external and load-bearing work; leaner mixes serve partitions and boundary panels. That call belongs to the engineer or the mason. This table exists so the call is made with both prices on the table.

Running The Same List For Your Wall

The method, in the order the mixer taught it to me:

1. Take the wall volume from your brick count. One cubic meter of wall is the unit; scale up or down from there.
2. Subtract the brick volume: bricks multiplied by 0.001539 cubic meters each. The remainder is wet mortar.
3. Multiply the wet mortar by 1.30 to get dry mortar.
4. Split the dry mortar by your mix ratio, and convert the cement share to bags at 50 kg each.

The concrete use case is the buyer standing at the building-materials shop with a brick count on his phone and no answer for the second question the shopkeeper always asks: how many bags, and how much sand. The 10 By 10 Wall Count in this series ends at 929 bricks; this article continues from that exact wall to its 3.21 bags and 0.45 cubic meters of sand at 1:4. Two lists, one wall, no rickshaw at noon. Order the mortar with the bricks, from the same arithmetic, and the mixer stops only when the wall is finished.