A client calls: 20 metres long, 2.4 metres high, six-inch blocks, plastered and painted both sides, with a gate opening. They want a figure by evening. Here is how to get to a defensible number without opening a fresh spreadsheet.
Step 1: measure once, in areas
Almost everything in a wall is priced by the square metre of wall face, so start there.
wall area = 20 m × 2.4 m = 48 m² less gate = 3.0 m × 2.1 m = 6.3 m² net wall area = 41.7 m² plaster/paint = 41.7 m² × 2 faces = 83.4 m²
Step 2: convert area to materials with fixed factors
These factors barely change from job to job. Once they are written down you never derive them again.
| Item | Factor | Quantity for 41.7 m² |
|---|---|---|
| 6-inch blocks | 12.5 per m² | 521 blocks |
| Cement for mortar | 0.35 bag per m² | 15 bags |
| Sand for mortar | 0.02 trip per m² | 0.83 trip |
| Plaster cement | 0.28 bag per m² of face | 23 bags |
| Plaster sand | 0.018 trip per m² of face | 1.5 trips |
| Emulsion paint | 0.02 unit per m² of face | 1.7 units |
| Putty | 0.05 bag per m² of face | 4.2 bags |
Sand and chippings are bought by the trip, not the cubic metre, so round up to whole trips and say so in the quote. Nobody delivers 0.83 of a trip.
Step 3: the foundation nobody quotes
A boundary wall is a structure. It needs excavation, a strip footing, a few courses below ground and — on most Accra plots — columns at intervals to handle wind load and poor ground.
- Excavation: 20 m × 0.6 m wide × 0.6 m deep ≈ 7.2 m³
- Strip footing concrete: about 0.18 m³ per metre run ≈ 3.6 m³
- Columns: one every 3 m gives 7 columns, each about 0.1 m³ plus reinforcement
- Below-ground blockwork: two to three courses across the full length
Step 4: the six lines that get forgotten
In our own reviews of contractor estimates, these are the omissions that appear most often on wall and fence jobs.
- 1.Haulage. Blocks, sand and chippings arrive on trips. Two or three trips at Accra rates is real money and is nobody’s free delivery.
- 2.Waste and breakage. Blocks break in transit and on site. Five to ten percent on blocks and tiles is not padding, it is observation.
- 3.Water. Curing a wall in dry season means a tanker, or you accept cracking.
- 4.Setting out and site clearing. Half a day of labour before a single block is laid.
- 5.Gate and ironmongery. Frame, leaf, hinges and painting — often a third of the wall’s value if the client wants steel.
- 6.Site clean-up and disposal. Excavated spoil has to leave the plot.
Step 5: price it, then check the margin
Apply your own rates to the quantities, add overhead, contingency and the markup that produces the margin you decided on, and then look at the finished number as a rate per square metre of wall. If it is wildly different from the last wall you built, one of your quantities is wrong. That single sanity check catches more errors than re-reading the whole estimate.
The fastest estimators are not the ones who type quickly. They are the ones who never derive the same factor twice.
— A quantity surveyor in Kumasi, on why he keeps a notebook of rates
Turning this into an assembly
Everything above is repeatable. One square metre of six-inch blockwork always consumes the same blocks, cement, sand and mason hours. Store it once as a composite rate and the next wall takes four minutes: measure the area, apply the assembly, add the foundation, add the gate, check the margin.