Division B
Acceptable Solutions

Part 9 — Housing and Small Buildings

Section 9.28. Stucco

9.28.1. General

9.28.1.1. Sheathing beneath Stucco
1) Intent StatementSheathing shall be provided beneath stucco applied over wood-frame walls except as permitted in Article 9.28.4.2.
2) Intent StatementWhere applied beneath stucco, sheathing shall conform to Subsection 9.23.17.
9.28.1.2. Lath and Reinforcing
1) Intent StatementStucco lath or reinforcing shall be used to attach stucco to any substrate other than masonry.
2) Intent StatementStucco lath or reinforcing shall be used to attach stucco to masonry where
a) the masonry is soft-burned tile or brick of less strength than the stucco, or
b) the masonry surface is not sound, clean and sufficiently rough to provide a good key.
3) Intent StatementStucco applied over masonry chimneys shall be reinforced.
9.28.1.3. Concrete Masonry Units
1) Intent StatementStucco finish shall not be applied over concrete masonry units less than one month old unless the units have been cured by the autoclave process.
9.28.1.4. Clearance over Ground Level
1) Intent StatementStucco shall be not less than 200 mm above finished ground level except when it is applied over concrete or masonry.
9.28.1.5. Flashing and Caulking
1) Intent StatementFlashing and caulking used with stucco shall conform to Subsections 9.27.3. and 9.27.4., except that if aluminum flashing is used, it shall be separated from the stucco by an impervious membrane or coating. (See Article 9.7.6.2. for caulking around window frames.)

9.28.2. Stucco Materials

9.28.2.1. Portland Cement
1) Intent StatementPortland cement shall conform to CAN/CSA-A3001, “Cementitious Materials for Use in Concrete.”
9.28.2.2. Aggregate
1) Intent StatementAggregate shall be clean, well-graded natural sand or sand manufactured from crushed stone, gravel or air-cooled blast furnace slag and shall contain no significant amounts of deleterious material.
2) Intent StatementAggregate grading shall conform to Table 9.28.2.2.
Table 9.28.2.2.
Aggregate Grading for Stucco
Forming part of Sentence 9.28.2.2.(2)

Sieve Sizes, mm (in.)

 % Aggregate Passing Sieve
Maximum Minimum

4 (.16)

 — 100

2 (.08)

 — 90

1 (.04)

 90 60

0.5 (.02)

 60 45

0.25 (.01)

 30 10

0.125 (.005)

 5 —
9.28.2.3. Water
1) Intent StatementWater shall be clean and free of significant amounts of deleterious material.

9.28.3. Fasteners

9.28.3.1. Materials
1) Intent StatementFasteners for stucco lath or reinforcing shall be corrosion-resistant and of a material other than aluminum.
9.28.3.2. Nails and Staples
1) Intent StatementNails for stucco lath or reinforcing shall be not less than 3.2 mm diam with a head diameter of not less than 11.1 mm.
2) Staples for stucco lath or reinforcing shall be not less than 1.5 mm diam or thickness.

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3) Intent StatementStaples and nails for attaching stucco lath or reinforcing to vertical surfaces shall be of sufficient length to penetrate 25 mm into framing members or to the full depth of the sheathing where the sheathing is used for attachment.
4) Intent StatementOn horizontal surfaces nails for stucco lath or reinforcing shall be not less than 38 mm long.

9.28.4. Stucco Lath

9.28.4.1. Materials
1) Intent StatementRib lath or expanded metal stucco mesh shall be
a) copper-alloy steel coated with rust-inhibitive paint after fabrication, or
b) galvanized.
2) Intent StatementWoven or welded wire mesh shall be galvanized.
9.28.4.2. No Sheathing Required
1) Intent StatementSheathing need not be provided beneath stucco where not less than 1.19 mm diam galvanized wire is applied horizontally to the framing at vertical intervals of not more than 150 mm, or where paper-backed welded wire metal lath is used.
9.28.4.3. Stucco Lath Specifications
1) Intent StatementStucco lath shall conform to Table 9.28.4.3.
Table 9.28.4.3.
Stucco Lath
Forming part of Sentence 9.28.4.3.(1)
Location Type of Lath

Minimum Diam of Wire,
mmchange begin(1)change end

 Maximum Mesh Opening

Minimum Mass, kg/m2
Vertical surfaces Welded or woven wire

1.15

25 mm

 —

1.30

38 mm

 —

1.50

51 mm

 —
Stucco mesh reinforcing (expanded metal) —

25.8 cm2

0.98

Horizontal surfaces(2)

9.5 mm rib lath

 — —

1.84
Cedar lath — — —
Notes to Table 9.28.4.3.:
(1) Wire with other than a circular cross-section is acceptable if it’s cross-sectional area is equal to or greater than that of the wire listed.
(2) See Appendix A.

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9.28.4.4. Self-Furring Devices
1) Intent StatementStucco lath shall be held not less than 6 mm away from the backing by means of suitable self-furring devices.
9.28.4.5. Application of Stucco Lath
1) Intent StatementStucco lath shall be applied with the long dimension horizontal.
2) Intent StatementHorizontal and vertical joints in stucco lath shall be lapped not less than 50 mm.
3) Intent StatementEnd joints of stucco lath shall be staggered and shall occur over framing members.
4) Intent StatementExternal corners of stucco lath shall be reinforced with a vertical strip of lath or reinforcing extending not less than 150 mm on both sides of the corner, or the lath or reinforcing shall extend around corners not less than 150 mm.
9.28.4.6. Fastening
1) Intent StatementStucco lath shall be fastened in conformance with Subsection 9.27.5.
2) Intent StatementFasteners on vertical surfaces shall be spaced not more than
a) 150 mm o.c. vertically and 400 mm o.c. horizontally, or
b) 100 mm o.c. vertically and 600 mm o.c. horizontally.
3) Intent StatementNailing patterns other than those required in Sentence (2) are permitted to be used provided there are at least 20 fasteners per square metre of wall surface.
4) Intent StatementFasteners on horizontal surfaces shall be spaced not more than
a) 150 mm o.c. along the framing members when members are spaced not more than 400 mm o.c., and
b) 100 mm o.c. along members when members are spaced not more than 600 mm o.c.

9.28.5. Stucco Mixes

9.28.5.1. Mixes
1) Intent StatementStucco mixes shall conform to Table 9.28.5.1.
Table 9.28.5.1.
Stucco Mixes
Forming part of Sentence 9.28.5.1.(1)
Materials, volume
Portland Cement Masonry Cement Lime Aggregate
1 — 0.25 to 1 3.25 to 4 parts per part of cementitious material
1 1 —
9.28.5.2. Pigments
1) Intent StatementPigment if used shall consist of pure mineral oxides inert to the action of sun, lime and cement.
2) Intent StatementPigment shall not exceed 6% of the Portland cement by weight.
9.28.5.3. Mixing
1) Intent StatementMaterials shall be thoroughly mixed before and after water is added.
2) Intent StatementStucco shall be applied not later than 3 h after the initial mixing.

9.28.6. Stucco Application

9.28.6.1. Low Temperature Conditions
1) Intent StatementThe base for stucco shall be maintained above freezing.
2) Intent StatementStucco shall be maintained at a temperature of not less than 10°C during application, and for not less than 48 h afterwards.
9.28.6.2. Number of Coats and Total Thickness
1) Intent StatementStucco shall be applied with at least 2 base coats and one finish coat, providing a total thickness of not less than 15 mm, measured from the face of the lath or the face of the masonry where no lath is used.
9.28.6.3. First Coat
1) Intent StatementThe first coat shall be not less than 6 mm thick, measured from the face of the lath or masonry, fully embedding the lath.
2) Intent StatementThe surface of the first coat shall be scored to provide a key with the second coat.
9.28.6.4. Second Coat
1) Intent StatementThe second coat shall be not less than 6 mm thick.
2) Intent StatementThe surface of the second coat shall be lightly roughened to provide a key with the finish coat if the finish coat is other than stone dash.
9.28.6.5. Finish Coat
1) Intent StatementWhen the finish coat is other than stone dash, the base shall be dampened but not saturated before the finish coat is applied.
2) Intent StatementThe thickness of the finish coat shall be not less than 3 mm.
3) Intent StatementWhen a stone dash finish is used, the stone shall be partially embedded in the second coat before the second coat starts to set or stiffen.