Masonry — Category 4

Envelope

CMU Sizes (CSA A165)

Nominal (mm)	Actual (mm)	Typical Use
200×200×400	190×190×390	Std load-bearing, fdn
250×200×400	240×190×390	Thick fdn, tall walls
300×200×400	290×190×390	Heavy load-bearing
150×200×400	140×190×390	Interior partitions
100×200×400	90×190×390	Veneer backup, infill

Mortar Types (CSA A179)

Type	Cem:Lime:Sand	Str. (MPa)	Use
S	1 : ½ : 4½	12.4	Below grade, structural, ext.
N	1 : 1 : 6	5.2	Above-grade veneer, int.
M	1 : ¼ : 3	17.2	Fdn below grade, retaining

Mortar life: 2½ hrs max (1½ hrs if >30°C). No retempering.

Grout (CSA A179)

Min. 12.5 MPa at 28 days; slump 200–250 mm
Max pour height: 4800 mm (fine grout, cells ≥50×75 mm)
Vibrate with 25 mm pencil vibrator; reconsolidate within 30 min

Key Dimensions & Spacing

Item	Value
Modular brick (actual)	90 × 57 × 190 mm
Bed & head joint	10 mm target
3 courses CMU + joints	= 600 mm (coursing check)
Wall tie spacing (CSA A370)	600 mm H × 400 mm V
Tie embedment (min.)	50 mm each joint
Cavity air space (min.)	25 mm clear (50 mm pref.)
Weep holes	600 mm o.c. above all flashing
CMU control joints	≤ 6 m intervals
Brick expansion joints	6–9 m intervals
Lintel bearing (min.)	100 mm (<1800) / 200 mm (>1800)
Flashing end laps	150 mm min., sealed & dammed
Shelf angle soft joint	10–15 mm (backer rod + sealant)

Reinforcement & Cleaning

Rebar in Masonry

Min. cover from CMU shell: 15 mm clear
Lap splices: 40 bar diameters (10M, 15M, 20M) in grouted cells
Horizontal joint reinforcement: every 400 mm vert. (typ.)
Clean-outs required for lifts > 1500 mm
Inspection hold point: rebar + clean-outs before grouting

New Masonry Cleaning

Wait min. 7 days before cleaning
Pre-wet wall; apply cleaner bottom-up; rinse top-down
Never use raw muriatic acid — use proprietary cleaner
No wire brushes on face brick
Test panel (1 m²) first; evaluate after 24 hrs

Code References

CSA A165: Concrete Masonry Units — sizes & specs
CSA A179: Mortar & Grout for Unit Masonry — mix ratios, retempering
CSA A370: Connectors for Masonry — wall tie material & spacing
CSA A371: Masonry Construction for Buildings — workmanship, grouting
O. Reg. 213/91: Construction Projects — scaffolding, Working at Heights
O. Reg. 490/09: Designated Substances — silica dust controls
401A: Brick & Stone Mason — compulsory trade in Ontario

Safety — Do Not Forget

Compulsory trade: Must hold 401A C of Q or be registered apprentice.
Silica dust: Wet-cut all masonry. Min. N95 for any dry cutting. Silica awareness training mandatory (O. Reg. 490/09).
Working at Heights: Approved training required before any scaffold access (O. Reg. 213/91 s. 26.2).
Scaffold guardrails: Top rail 1050 mm ± 50 mm, mid-rail, toeboard ≥ 100 mm.
Scaffold loading: Never exceed rated capacity; distribute materials evenly.
No retempering: Discard mortar past its working life — no adding water.

Pro Tips

Blend brick: Pull from 5+ cubes to prevent colour banding on the facade.
Cavity check: Drop a weighted line down the cavity at every 3rd weep hole to verify no mortar bridges before closing up.
Set leads with a transit/laser on walls > 20 m — a 2 mm error at the lead compounds into a visible bow.
Tool joints at thumbprint-hard — window can be as short as 20 min on hot days.