Measurement and Quantities
Measurement questions test whether you can take off quantities in a defensible order and convert them to bags of cement, cubic metres of sand and numbers of blocks. State your rules, apply them consistently, and round only at the end.
Principles
Take off in the sequence the work is done, describe each item fully, measure net, and state the deduction rule you are using. Units: linear metres to 2 decimal places, square metres to 2 dp, cubic metres to 2 dp, countable items in whole numbers.
Methods
- Centre-line method: best when all walls are the same thickness - total centre-line length × width × height, with corners counted once.
- Long wall/short wall: use when wall thicknesses differ; short walls are reduced by the thickness of the long walls at each junction.
- Floor-area method: quick estimating from blocks per m² and cement per m².
Constants worth memorising
- 450 × 225 × 150 mm blocks with 10 mm joints: 9.25 per m² of wall face.
- Dry-volume factor: 1.33 for mortar, 1.54 for concrete.
- Cement: 1440 kg/m³, so a 50 kg bag is about 0.035 m³.
- 1 m³ = 1000 litres.
Worked example
Mortar and cement for 13.68 m² of 150 mm blockwork using 127 blocks. Wall volume = 13.68 × 0.15 = 2.052 m³. Block volume = 127 × (0.45 × 0.225 × 0.15) = 127 × 0.01519 = 1.929 m³. Wet mortar = 2.052 − 1.929 = 0.123 m³. Dry mortar = 0.123 × 1.33 = 0.164 m³. For a 1:4 mix (5 parts), cement = 0.164 ÷ 5 = 0.0328 m³ × 1440 = 47 kg, that is one 50 kg bag; sand = 0.0328 × 4 = 0.131 m³. Reasoning: mortar is what is left after the blocks, then bulked to dry volume before splitting by the mix parts.
Traps that cost marks
Forgetting to deduct openings; using wet instead of dry volume; mixing millimetres and metres in one line; double-counting corners in the long wall/short wall method; omitting waste and breakage; measuring to the outside face when the drawing dimensions to the centre line.
Communication, Numeracy and Entrepreneurship
This domain tests the non-trade skills that decide whether a good mason makes money: clear site communication, correct arithmetic under pressure, and pricing and record-keeping that survive a client’s questions.
Site communication
- Written: drawings and specifications, bills of quantities, site instructions, requests for information, the site diary, delivery notes, daywork sheets, minutes and the drawing register.
- Verbal: briefings, toolbox talks, hand signals to plant operators, two-way radio. Confirm verbal instructions in writing the same day, record all deliveries against the note before signing, and report accidents and near-misses immediately.
Numeracy for the trade
Ratios and percentages, unit conversion, labour and material constants, wages and overtime, simple interest, discounts, profit and loss, average output per gang per day. Always write the unit at every step - most lost marks here are unit errors, not arithmetic errors.
Running a small contracting business
Register the business with the Office of the Registrar of Companies, obtain a Business Operating Permit from the District or Municipal Assembly, and register with the Ghana Revenue Authority for a TIN; VAT registration applies once turnover passes the threshold (confirm current rates and levies with GRA, as they change). Price a job as materials + labour + plant + subcontractors + overheads + contingency + profit. Keep a cash book, invoices, receipts and quotations; a quotation is a fixed offer valid for a stated period, an estimate is not. Manage cash flow with mobilisation payments, stage invoicing and retention (commonly 5–10%).
Worked example
Materials GH₵4,800, labour GH₵2,200, plant GH₵600, so direct cost = GH₵7,600. Overheads at 8% = GH₵608, giving GH₵8,208. Contingency at 5% = GH₵410.40, giving GH₵8,618.40. Profit at 15% = GH₵1,292.76, so the quotation is GH₵9,911.16, say GH₵9,911. Note the trap: GH₵1,292.76 ÷ GH₵9,911.16 = 13.0%, so a “15% mark-up” is only a 13% margin - if the client asks for a 15% margin, divide by 0.85 instead.
Traps that cost marks
Confusing mark-up with margin; quoting from memory without measuring; forgetting overheads and transport; giving a verbal price that later changes; not keeping copies of quotations and delivery notes; treating VAT collected as your own money.
Practical Project Work and Trade Assessment
The practical project is where the trade is judged by hand rather than by pen. Candidates normally receive a drawing and a short specification and must set out and build a blockwork corner, pier or short wall - or cast and finish a small reinforced element - within a set time, usually one working day or less. Assessment is by observation against a checklist, so work method matters as much as the finished job.
What the assessor looks for
- Setting out accuracy within about ±5 mm, checked with a tape and the 3-4-5 method.
- Plumb checked with a spirit level and plumb bob on every course; level checked across every course.
- Gauge and joint thickness about 10 mm, consistent, with full bed and perpend joints.
- Correct bond, correct block orientation, clean arrises.
- Mortar of the right consistency, mixed in the right proportion, not revived with water.
- PPE worn from the start, tools handled safely, scaffold used correctly.
- Housekeeping, tool cleaning, and handover with the face left clean.
- Time taken within the allowance; dimensions matching the drawing.
Working method
Read the drawing and specification → take off the materials → collect and check the tools → set out with lines and profiles → build the corners first → line and fill → check level and plumb after every course → point and clean down → self-check with tape, level and plumb bob → hand over.
Worked example
Build two legs of 225 mm blockwork forming a corner, each 1.2 m long and 1.2 m high, from 450 × 225 × 150 mm blocks. Course height 235 mm, so 1.2 ÷ 0.235 = 5.1, meaning five full courses (1.175 m) plus the bedding course. Blocks per leg per course = 1.2 ÷ 0.46 = 2.6, so three blocks with one cut. The legs share the corner block, so per course 3 + 3 − 1 = 5 blocks. Total = 5 courses × 5 = 25 blocks; add 5% for cutting = 27, so request 30. Mortar at 1:4 for this volume needs roughly one and a half 50 kg bags of cement - order two.
Traps that cost marks
Starting to lay without reading the drawing; putting PPE on only when the assessor appears; laying fast with no level checks and discovering a 20 mm lean at the top; leaving mortar smears on the face; tools dirty at handover; not curing or protecting the finished work; running out of time because materials were not staged before starting.