Masonry Unit Preparation and Cutting

Preparation and Cutting of Masonry Units

Module Introduction

The preparation and cutting of masonry units is a fundamental step in the bricklaying trade. Before installation, every brick, block, or stone must be inspected, conditioned, and, when necessary, cut with precision. A poorly executed cut compromises the appearance, structural strength, and watertightness of the wall. This chapter covers all the theoretical and practical knowledge required for the Red Seal exam: types of units, tools, cutting methods, waste calculations, safety regulations, and applicable Canadian standards.

Types of Masonry Units and Their Preparation Requirements

Unit Classification

Masonry units are divided into three main families: fired clay bricks, concrete blocks (CMU – Concrete Masonry Units), and natural or manufactured stone. Each type has distinct physical characteristics that influence the cutting method.

Unit Type	Typical Strength (MPa)	Water Absorption (%)	Recommended Cutting Method
Fired clay brick	20 – 55	5 – 17	Wet saw, manual brick cutter
Lightweight concrete block	7 – 15	10 – 20	Wet saw, diamond saw
Heavy concrete block	15 – 35	5 – 12	Wet saw, diamond saw
Natural stone (granite)	100 – 250	0.1 – 0.5	Diamond saw, water jet
Manufactured stone	20 – 40	6 – 12	Wet saw, grinder

CSA A82 (Fired Clay Bricks) and CSA A165 (Concrete Blocks) define dimensional tolerances. A standard Canadian brick measures 190 mm × 90 mm × 57 mm (length × width × height), with variations of ± 2 mm acceptable. For blocks, the common nominal dimension is 390 mm × 190 mm × 190 mm.

Inspection and Conditioning

Before any cutting, you must visually inspect each pallet. Units that are split, chipped, or have through-cracks must be set aside. The Red Seal exam tests your ability to identify acceptable defects versus unacceptable defects.

Acceptable defects: minor chips on edges (less than 5 mm), colour variations, light efflorescence.

Unacceptable defects: cracks through the unit, chips exceeding 10% of the surface, excessive deformation (warping > 3 mm).

Conditioning involves wetting highly absorbent units before installation. The general rule: if water absorption exceeds 12% (measured according to CSA A82.1), bricks must be dampened 24 hours before installation. However, a saturated brick must never be laid — it would slide on the mortar. The goal is to achieve a surface that is "dry on the surface, damp in depth."

Calculating Waste and Quantities

Waste calculation is a skill assessed on the exam. Standard waste for manual cutting is 5 to 8%; for mechanical saw cutting, 3 to 5%. Additional waste for breakage, handling, and storage is added: 2 to 3%.

Calculation formula:

Total quantity = (Number of units installed) × (1 + waste rate)

Example: a 10 m² wall requires 50 bricks per m² (with 10 mm joints). Number of bricks installed = 500. With 8% waste: 500 × 1.08 = 540 bricks to order.

Common trap: the exam often includes waste for corner cuts, openings (doors, windows), and wall ends. For a wall with openings, first calculate the net area (gross area − opening area), then apply the waste rate. Never double the waste rate for openings — the waste is already included in the overall percentage.

Cutting Tools and Their Use

The Wet Saw (Masonry Saw)

The wet saw is the primary tool for cutting bricks and blocks. It uses a diamond blade cooled by water, which reduces dust and prevents blade overheating. Technical characteristics to know:

Rotation speed: 2,800 to 3,500 RPM for blades 350 to 450 mm in diameter.

Water flow rate: 6 to 10 L/min for effective cooling.

Maximum cutting depth: typically 150 to 200 mm depending on the model.

The feed rate must be constant. Feeding too quickly causes diamond segments to tear out; feeding too slowly polishes the blade and reduces its efficiency. The cutting sound is an indicator: a high-pitched sound indicates overheating, a low-pitched sound indicates a proper cut.

Portable Diamond Saw (Angle Grinder)

For on-site cuts, the angle grinder fitted with a dry (or wet) diamond blade is used. Blades of 115 mm and 230 mm are the most common. Dry cutting generates crystalline silica dust — a hazard recognized by CSA Z94.4 (respiratory protection). Wearing at minimum an N95 respirator is mandatory.

Manual Brick Cutter

The manual brick cutter (or "roller brick cutter") is used for clay bricks. It works by pressure: a tungsten carbide wheel scores a break line, then sudden pressure splits the brick. This method is fast but produces less precise cuts (± 3 mm). It is reserved for straight cuts and low-strength bricks (< 30 MPa).

Chisel and Mallet

For fine adjustments and precision cuts, the bricklayer's chisel (75 to 100 mm blade) and a 1.2 kg mallet are used. The technique involves scoring the brick on all four faces, then striking a sharp blow on the scored line. This method requires precise technique — a striking angle of 45° relative to the surface.

Advanced Cutting Techniques

Bevel Cut (Angle)

Bevel cuts are necessary for non-perpendicular wall angles (for example, a 135° angle). The method:

36.Measure the wall angle with a miter square or protractor.

37.Divide the angle by 2 to obtain the cutting angle for each brick.

38.Set the wet saw table to this angle.

39.Perform a test cut on a scrap brick.

Angle calculation: for a 120° wall angle, each brick must be cut at 60° (120° ÷ 2). The brick length after cutting is reduced according to the formula: L′ = L × cos(90° − θ), where θ is the cutting angle.

Radial Cut (for Arches and Curves)

Arches require radial cuts. The standard method:

43.Trace the arch on the wall using a compass or template.

44.Calculate the number of bricks needed: N = (π × D) / (L + e), where D is the arch diameter, L the brick length, and e the joint thickness.

45.Calculate the cutting angle: α = 180° / N.

46.Cut each brick at angle α, ensuring the longer side remains at the extrados (outer face of the arch).

Example: an arch with a 2 m diameter using 190 mm bricks with 10 mm joints. N = (π × 2000) / (190 + 10) = 6283 / 200 = 31.4 → round to 32 bricks. α = 180° / 32 = 5.6°.

Cutting Concrete Blocks

Concrete blocks (CMU) present particular challenges: their size (390 mm) and weight (15 to 20 kg) make handling difficult. Cutting is done almost exclusively with the wet saw. For 190 mm thick blocks, a single pass suffices; for 290 mm blocks, you must flip the block and cut from both sides.

Two-pass cutting technique:

51.First pass: cut to 50% of the thickness.

52.Flip the block over.

53.Second pass: align the cut line with the existing groove.

54.Complete the cut and check alignment with a square.

Cutting Natural Stone

Natural stone (granite, limestone, sandstone) requires specific diamond blades. Granite requires a continuous-rim (or "turbo") blade to prevent chipping. Limestone, being softer, can be cut with a segmented blade. The feed rate must be reduced by 30% compared to clay brick.

Safety Standards and Regulations

Crystalline Silica

Cutting masonry generates crystalline silica dust (quartz). Prolonged exposure causes silicosis, an irreversible lung disease. Canadian regulatory requirements are set out in the Canada Occupational Health and Safety Regulations (Part II of the Canada Labour Code) and equivalent provincial standards.

Mandatory control measures:

Use of wet saws (dust suppression through wet methods).

Source extraction for dry grinders.

Wearing a respirator (APR) with P100 filter.

Annual medical surveillance for exposed workers.

Machine Safety

CSA Z432 (Safeguarding of Machinery) applies to masonry saws. Key requirements:

The blade guard must be in place at all times.

The emergency stop switch must be accessible and tested daily.

The power cord must be inspected for damage before each use.

The machine must be grounded in accordance with the Canadian Electrical Code, Part I (Rule 8-200 for portable tools).

Manual Handling

Concrete blocks weigh up to 20 kg. CSA Z1004 (Manual Handling) recommends not lifting more than 23 kg per person without mechanical assistance. For heavier loads, use a forklift or a vacuum lifting device. Correct lifting techniques: straight back, bent legs, load close to the body.

Quality Control of Cuts

Dimensional Tolerances

CSA A371 (Concrete Masonry — Construction) defines installation tolerances. For cuts:

Length deviation: ± 3 mm.

Angle deviation: ± 2°.

Flatness deviation (cut surface): ± 2 mm over 300 mm.

Verifying Cuts

After each cut, check:

81.Squareness: use a mason's square to verify the 90° angle.

82.Flatness: place the cut brick on a flat surface — it must not rock.

83.The edge: the cut edge must be clean, without chips exceeding 2 mm.

Exam trap: a cut that appears correct but has a chip on the bottom edge (mortar side) is acceptable; a chip on the top edge (visible side) is unacceptable. The exam tests this distinction.

Special Cuts for Openings

For doors and windows, cuts must be precise to the millimetre. The method:

87.Measure the actual opening (after frame installation).

88.Subtract 10 mm for the expansion joint (2 × 5 mm).

89.Divide the remaining dimension by the modular brick length (190 mm + 10 mm joint = 200 mm).

90.Calculate the adjustment cut: if the result is not a whole number, the fraction represents the dimension of the cut brick.

Example: an opening of 1,210 mm. 1,210 − 10 = 1,200 mm. 1,200 / 200 = exactly 6 bricks — no cut needed. If the opening is 1,250 mm: 1,250 − 10 = 1,240. 1,240 / 200 = 6.2 → 6 full bricks + 1 brick cut to 0.2 × 200 = 40 mm. The cut brick must be placed at the centre of the opening, never at the ends.

Advanced Calculations for Preparation

Calculating the Number of Bricks per Square Metre

The general formula: N = 1 / [(L + e) × (H + e)], where L is the brick length, H the height, and e the joint thickness (in metres).

Example: brick of 190 mm × 57 mm, 10 mm joint.

N = 1 / [(0.190 + 0.010) × (0.057 + 0.010)] = 1 / (0.200 × 0.067) = 1 / 0.0134 = 74.6 bricks/m².

For 390 mm × 190 mm blocks with a 10 mm joint:

N = 1 / [(0.390 + 0.010) × (0.190 + 0.010)] = 1 / (0.400 × 0.200) = 1 / 0.080 = 12.5 blocks/m².

Calculating Actual Waste

Actual waste is calculated after cutting: Waste (%) = (Number of rejected units / Total number of units cut) × 100. The exam may ask you to calculate waste from a scenario: out of 250 bricks cut, 18 are rejected. Waste = (18 / 250) × 100 = 7.2%. This rate is acceptable (limit: 8%).

Optimizing Cuts

To minimize waste, plan cuts based on modular dimensions. A standard 190 mm brick can be cut into:

Half brick: 95 mm (for wall ends).

Three-quarter brick: 142.5 mm (for corners).

Quarter brick: 47.5 mm (for adjustments).

Golden rule: never cut a brick to less than 40 mm in length — it becomes structurally weak and difficult to lay.

Maintenance of Cutting Tools

Sharpening and Replacing Blades

A diamond blade wears normally and evenly. Signs of abnormal wear:

Polishing (shiny surface): the blade no longer cuts — resharpen by cutting an abrasive brick (fresh concrete) for 30 seconds.

Warping (deformation): replace the blade immediately.

Missing segments: replace the blade — risk of catastrophic failure.

The typical lifespan of a diamond blade is 50 to 100 m² of cutting for brick, 20 to 40 m² for concrete.

Daily Inspection

Before each use:

116.Inspect the blade for cracks, missing segments, or uneven wear.

117.Check belt tension (for wet saws).

118.Check the water reservoir level.

119.Test the emergency stop switch.

120.Verify that the cutting table is perpendicular to the blade (using a square).

Summary

Preparation of masonry units includes inspection, conditioning (dampening if absorption > 12%), and waste calculation (5 to 8% for manual cutting, 3 to 5% for mechanical cutting).

The main cutting tools are the wet saw (precision ± 1 mm), the angle grinder (flexibility), the manual brick cutter (speed, precision ± 3 mm), and the chisel/mallet (fine adjustments).

Special cuts (bevel, radial, openings) require precise angle and dimension calculations — the formula N = (π × D) / (L + e) for arches is essential.

Safety requires controlling silica dust (wet saw, extraction, P100 respirator), compliance with CSA Z432 for machinery and CSA Z1004 for handling.

Cutting tolerances according to CSA A371: ± 3 mm in length, ± 2° in angle, ± 2 mm in flatness.

Quantity calculations use the formula N = 1 / [(L + e) × (H + e)] — memorize it.

Diamond blade maintenance is crucial: inspect daily, replace if warped or if segments are missing.

Traps to Avoid

130.Confusing waste and rejects: waste includes handling breakage and failed cuts; rejects only concern unusable units. Do not add them together.

131.Forgetting to dampen: a highly absorbent brick laid without dampening draws water from the mortar too quickly, causing incomplete curing. Conversely, a saturated brick slides on the mortar.

132.Dry cutting without protection: silica dust is invisible but deadly. The exam tests your knowledge of protective equipment — never answer "dry cutting without a mask."

133.Calculating openings with double waste: the opening area is subtracted from the gross area, but the waste rate applies to the net area, not the gross area.

134.Ignoring the cutting direction: for clay bricks, always cut from the longest side to the shortest (from the bed to the face). Cutting in the opposite direction causes chipping.

135.Using a worn blade for natural stone: a blade designed for clay brick is not suitable for granite — it wears prematurely and produces imprecise cuts.

136.Neglecting squareness checks: a cut at 89° instead of 90° creates a cumulative deviation of 1° per brick — over 10 bricks, the wall deviates by 10°.

137.Always rounding up: for arches, round to the nearest whole number, then recalculate the cutting angle. Always rounding up creates excessively wide joints.

138.Forgetting the expansion joint at openings: the 10 mm clearance around door/window frames is mandatory — do not remove it to simplify calculations.

139.Confusing the standards: CSA A82 concerns clay bricks, CSA A165 concrete blocks, CSA A371 masonry construction. The exam may ask you which standard applies to which situation.