Wastage
Most contractors’ experience significant differences between the calculated quantity of mortar to be used and the actual quantity used, often as much as 20%-30%. Typical areas of concern are:
- Make sure the site where the cement is stored has good security to avoid theft.
- Where sand is being bought by volume, always measure the truck as this is often overlooked.
- When mixing, always use a level concrete surface and mechanical mortar mixers are preferred to hand mixing. The mixing area must be contained and not be allowed to spread out.
- Mixing from pockets is not always efficient as a full pocket must be mixed and used every time, which is not always possible. Are mix proportions consistently batched and homogeneously mixed?
- Counting wheelbarrows is not always accurate due to the varying sizes of the wheelbarrows.
- Irregular brickwork is also a factor as it requires a far thicker plaster coat than the normal 15-20mm normally allowed for.
- In summary, poorly supervised transporting, storing, mixing and application of mortar are the most common reasons for unacceptable losses.
YIELD
Wheelbarrows of sand vs wheelbarrows of dagha
Counting wheelbarrows of mortar is an inaccurate method of determining yield. Whilst a full wheelbarrow will yield 65 liters of
damp sand, mortar being virtually liquid will only be able to convey some 30 liters before spillage occurs during transportation.
One wheelbarrow of damp sand (651) DOES NOT = one wheelbarrow of mortar (30-352)
Solid bricks vs perforated bricks
Often overlooked is the amount of extra mortar required when laying bricks with frogs or perforated with cavities. Illustrated below are examples of how mortar quantities can escalate.
Amount of mortar required to cover one vertical and one horizontal surface = 320ml
Amount of mortar required to cover two surfaces plus an additional 3 cavities = 770ml (140% extra)
Amount of mortar required to cover two surfaces plus allwafer cavities = 820ml (156% extra)
SPECIFICATIONS
Mortar classes, mix proportions and strength (most common mortar used is Class II)
References
Concrete/Beton April 1995 Issue No 76 SABS 0164 Part 1 1980.