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1.01 Scope
This specification covers the minimum requirements for
the application of a stucco
system, including general information pertaining to
the design and application of stucco.
NOTE:
• This specification serves as a guide for the
development of a specification
for a particular project.
1.02 Contractor
Scope of Work
The work of this section includes all the equipment,
materials and labor necessary to
complete a stucco system, as indicated in this Stucco
Resource Guide and/or in project
documents (drawings and specifications).
1.03 Related
Sections (Section numbers
may be different depending upon specification format)
A. Section 01200 —
Project Meetings
B. Section 01630 —
Substitutions
NOTE:
• Product substitutions will be considered only
under the terms and
conditions of section 01630.
C. Section 03300 —
Concrete
D. Section 04220 —
Unit Masonry
E. Section 05410 —
Load-Bearing Steel Studs
F. Section 06110 —
Wood Framing
G. Section 07240 —
Exterior Insulation and Finish Systems
H. Section 07600 —
Flashing and Sheet Metal
I. Section 07900 —
Joint Sealants
J. Section 09110 —
Non-Load-Bearing Steel Studs
K. Section 09250 —
Gypsum Sheathing Board
L. Section 09900 —
Painting
Details in this Stucco Resource Guide may show a single
layer of water-resistant
barrier for drawing clarity only. Refer to the Guide
Specification
section 3.38-B. The recommendation is for two layers.
1.04 Reference
Standards
A. National Building
Code — Canada
B. City Building Code
— Vancouver, B.C.
C. Building Codes - International,
NFRA, California, Uniform
D. Stucco Resource Guide
(NWCB)
E. American Concrete Institute
ACI 524R: Guide to Portland Cement Plastering
F. Federal Specifications
FS UU-B-790a: Building Papers, FS FF-N-105B: Nails,
Wire Staples for Application of Gypsum Board, FS QQ-W-461H:
Wire, Steel and Carbon (round
, bare & coated)
G. Portland Cement Plaster
(Stucco) Manual by PCA
H. ASTM Standards
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ASTM A526:
Steel Sheet, Hot-Dip Galvanized, Commercial Quality
ASTM C91: Masonry
Cement
ASTM C144: Aggregate
ASTM C150: Portland
Cement
ASTM C1328: Plastic
Cement
ASTM C206: Hydrated
Lime
ASTM C260: Air-Entraining
Admixtures
ASTM C494: Chemical
Admixtures for Concrete
ASTM C841: Installation
of Interior Lathing and Furring
ASTM C847: Metal Lath
ASTM C897: Aggregate
for Job-Mixed Portland Cement Plaster
ASTM C926: Application
of Portland Cement-Based Plaster
ASTM C932: Surface-Applied
Bonding Agents for Exterior Plastering
ASTM C979: Pigments
for Integrally Colored Concrete
ASTM C1032: Woven
Wire Plaster Base
ASTM C1063: Installation
of Lathing and Furring for Portland Cement Plaster
ASTM D1784: Rigid
Poly (Vinyl Chloride) PVC Compounds |
I. NAAMA Standard ML/SFA 920
NOTE:
• Current editions at date of bid.
• Use references and standards applicable to project.
1.05 Standards for Work
All work to be performed per Northwest Wall and Ceiling
Bureau recommendations.
A. Stucco Resource Guide and project construction documents.
NOTE:
• Project construction documents to indicate type
of stucco assembly.
(Refer to “Stucco Assemblies”
section of this Stucco Resource Guide).
1.06 Submittals
A. Submittal requirements
by the stucco contractor are to be indicated in the
construc-tion documents. The following is a list of
documents that may be requested.
1. Product literature.
2. Samples and/or mock-ups
of system.
3. Certification of compliance
of materials and/or product literature.
4. Product literature
for all additives and proprietary components.
5. Finish sample for texture
and color for architect/owner approval.
NOTE:
• Delete submittals not required.
• Plastering contractor is not to proceed with
work until the required
submittals have been approved.
1.07 Quality
Assurance for Scope of Stucco Work
A. Pre-installation meeting.
B. Wall assembly fire-resistance
rating: _______ hour(s).
NOTE:
• Construction documents shall indicate the type
of fire and/or sound
assembly rating required for project.
• Construction documents to indicate fire-resistance
assembly test
required.
C. “Scope of Work
Responsibilities Tables” section of this Stucco
Resource Guide.
D. “Stucco Quality
Assurance Checklist” section of this Stucco Resource
Guide.
E. If required and feasible,
an approved finish coat on a portion of the building.
Location of finish coat sample as directed by the architect.
NOTE:
• Delete if not applicable.
F. Applicator qualifications.
The plastering company shall meet the following
requirements:
1. Specialize in this
scope of work.
2. Have qualified and
properly trained people to perform work.
3. Be licensed, bonded
and insured.
4. Be in good financial
standing and capable of meeting the financial obligations
associated with the stucco scope of work on the project.
5. Have documented experience
in quality work of comparable scope.
6. Be recommended as a
qualified installer by NWCB or national or regional
Wall
and Ceiling Association (Plastering Association) or
approved by architect prior
to bid.
7. Contractor shall be
able to meet schedule requirements set at time of bid.
1.08 Delivery,
Storage, Handling and Setup
A. Materials at job site
to be in original containers with labels intact and
legible.
NOTE:
• Exception: Basecoat sand
B. All trim accessories
and lath and/or other specified products to be shipped
to job site
in original containers. Any damaged or bent materials
shall be replaced.
C. All sack materials
to be stored above ground, dry and protected.
NOTE:
• General contractor shall provide suitable site
for delivery, storage and
handling of materials.
• General contractor shall provide suitable site
for plastering operation.
1.09 Environmental Conditions
A. Cold Weather Conditions:
1. Do not apply cement
plaster when ambient temperature is less than 35....F
(2....C).
2. Do not apply cement
plaster to any frozen surfaces or surfaces containing
frost.
Protect plaster coats against freezing for a period
of 24 hours after application.
3. Do not use frozen materials.
4. Hoarding (tenting),
heat and ventilation must be provided if cement plastering
is done in a temperature below 35....F (2....C).
NOTE:
• The plastering contractor is not responsible
for these requirements.
• Maintain adequate ventilation. Vent heaters to
outside.
5. Admixtures of cement
plaster for cold weather condition must be approved
and
used in accordance of manufacturer’s recommendations.
B. Warm Weather Conditions:
1. Protect the basecoats
and finish coat of cement plaster from uneven and
excessive evaporation in warm, windy weather. (Refer
to section on curing in
Part III)
NOTE:
• Moist-curing is recommended.
2.01 Weather-Barrier
Backing/Water-Resistant Barrier
A. Water-resistant paper—Federal
Specification UU-B-790a, grade D/30-minute or 60-
minute
B. Spunbonded olefin housewrap
manufactured and designed specifically for stucco.
C. Flashing material around
rough wall openings shall be a reinforced coated vapor-barrier,
grade A or B product, sheet metal, PVC plastic, or other
approved
membrane. The application of the flashing is not the
responsibility of the stucco contractor. Refer to the
“Scope of Work Responsibilities” section of
this Stucco
Resource Guide.
2.02 Window head, door, louver
and/or other penetration-plus wall opening pan-type
flashing - 26-gauge galvanized sheet metal, or PVC plastic.
NOTE:
• Construction documents to indicate responsibility
for installation of
window head flashing and other stucco component flashing.
2.03 Tie Wire
Hanger and tie wire to be galvanized and annealed low-carbon
steel:
FSQQ-W-461g. AS
A. Hanger wire No. 8—.1620
inch (4.12 mm)
B. Tie wire 18 gauge—.0475
inch (1.22 mm)
C. Tie wire 16 gauge—.0625
inch (1.59 mm)
2.04 Runner- and Cross-Furring
Channels
Cold-rolled galvanized steel channels, 1 1/2 inches
(38 mm) and 3/4 inches
(19 mm), a
minimum of 33,000 psi yield strength and a minimum of
.0538-inch bare steel thickness,
ASTM A526.
NOTE:
• Suspended soffits/ceilings—1 1/2-inch (38
mm) main runner, 3/4-inch
(19
mm) cross furring.
2.05 Furring “Hat”
Channels
Furring channel, galvanized 7/8-inch (22
mm), 20-gauge.
2.06 Fasteners Shall Comply
with:
A. Nails—FS FF-N-105
B. Staples—FS FF-N-105
C. Screws—ASTM C
646
D. Power-driven fasteners—per
building code approval
NOTE:
• All fasteners to be corrosion-resistant and new.
2.07 Lath
NOTE:
• Architect/specifier to indicate in construction
documents the type or
types of lath (A, B, C or D).
Delete types of lath not applicable.
• Self-furring paperback lath (a
combination of lath and grade D 60-
minute water-resistant barrier) is not recommended
over a vertical
concrete or concrete masonry surface if the construction
documents.
require a water-resistant barrier for these surfaces.
A. Self-furring woven wire lath 17 gauge—1 1/2-inch
(38 mm) opening, galvanized.
Shall comply with ASTM 1032.
NOTE:
• For vertical surfaces only.
B. Self-furring diamond-mesh metal lath galvanized,
2.5 or 3.4 pounds per square yard.
Shall comply with ASTM 847.
NOTE:
• 2.5-pound-per-square-yard self-furring lath may
be used for a sheathed
framing construction system, 16 inches (400
mm) o.c., or for attachment
directly to concrete or concrete masonry.
C. Self-furring welded
wire lath, 16 gauge wire, galvanized openings not to
exceed 2
inches x 2 inches (50 mm x 50
mm). Shall comply with ASTM 933.
NOTE:
• For vertical surfaces only.
D. 3/8-inch (10
mm) rib lath, galvanized. ASTM 847
NOTE:
• For soffit condition with open-frame construction,
with supports 24
inches (600 mm) o.c.
2.08 Trim Accessories
NOTE:
• Trim Accessories shall be fabricated from galvanized
steel, zinc (alloy),
PVC or anodized aluminum.
• Depth (the grounds)
of accessories depends on the required thickness of
cement plaster basecoat, without the finish coat.
• If the construction documents do not indicate
the type of accessories to
be installed, the plastering contractor shall select
the accessories in
accordance with these standards.
• Accessories of PVC plastic or zinc (alloy)
are recommended if corrosion
is a concern because of environmental conditions.
• Accessories with a finish surface lip flange
and/or embedment flange to
key into cement plaster are recommended.
• It is recommended that PVC or aluminum reveals,
when used in
conjunction with 2-inch x 2-inch welded wire lath, incorporate
a strip of
expanded metal lath over the solid reveal flanges.
A. Steel accessories
per ASTM C 841
B. PVC plastic accessories
per ASTM D 1784 & C 1063
C. Aluminum accessories
from extruded alloy 6063 T5
D. General types of accessories:
1. Foundation weep screed:
______________________________________
2. Casing bead type no.
66 (JMOLD): _______________________________
3. Corner reinforcement
(corner bead): ______________________________
NOTE:
• No. 1A expanded corner beads for interior gypsum
plaster are not
recommended.
E. Soffit vents ______________________________
F. Drip screeds ______________________________
G. Trim accessory joints
(control joints), expansion joints, or revels____________
NOTE:
• Construction documents shall reference type,
style and manufacturers of
accessories.
• Delete accessories not applicable for the project.
2.09 Bonding Agents
Bonding agents must conform to ASTM C 932, nonoxidizing,
non-crystallizing,
non-re-emulsifiable.
NOTE:
• Apply per manufacturer’s recommendations.
• Apply bonding agents only to clean, structurally
sound surfaces
(concrete, concrete masonry and
cement plaster).
• Indicate manufacturer and brand name.
• Delete if not applicable.
2.10 Plaster Materials
NOTE:
• Delete cements not applicable.
A. Stucco basecoat
1. Portland Cement: ASTM
C 150 Type I or Type I/II
2. Masonry Cement: ASTM
C 91 Type I or Type I/II
3. 1-P Portland Cement:
ASTM C 595
4. Manufactured basecoat
cement for stucco
NOTE:
• Indicate manufacturer as per NWCB and/or regional
wall and ceiling
association recommendation.
B. Hydrated lime: ASTM
C 206 Type S
C. Stucco finish
1. White portland cement,
ASTM 150 Type I or Type I/II
2. Regular portland cement,
ASTM 150 Type I or Type I/II
3. Manufactured stucco
finish
NOTE:
• Indicate manufacturer as per NWCB and/or regional
wall and ceiling
association recommendation.
NOTE:
• Do not use frozen aggregate.
A. Basecoat sand
NOTE:
• ASTM C144 or C897
• Natural or manufactured
• Washed and free of deleterious materials
• Locally available sand that approximates ASTM
C144 or C897, but
which may be nonconforming, can be approved for use
if past perfor-mance
indicates that it is an appropriate material.
B. Finish coat sand
NOTE:
• ASTM C897
• Natural or manufactured
• Freshwater washed and free of deleterious materials
• Locally available sand that approximates ASTM
C144 or C897, but
which may be nonconforming, can be approved for use
if past perfor-mance
indicates that it is an appropriate material.
2.12 Water Potable, clean, free
from impurities.
2.13 Admixtures
NOTE:
• No household-type detergents or chlorides shall
be permitted.
• Only admixtures manufactured specifically and
approved for use in a
stucco mix shall be permitted.
• Admixtures without supporting documentation and
appropriate testing
or industry performance will not be approved by the
NWCB and/or
regional wall and ceiling association.
A. Fibers: 1/2-inch (13
mm) long, ASTM C 1116
NOTE:
• Recommended as part of basic basecoat mix.
• Only in basecoats, not in finish coat.
• Polypropylene, nylon or alkali-resistant glass
fibers.
• Use only types specifically manufactured for
a stucco basecoat and per
manufacturer’s recommendations.
B. Air-entraining admixtures:
NOTE:
• ASTM C 260
• Amount used shall be consistent with manufacturer’s
recommendations.
• Use only products approved by the NWCB and/or
regional wall and
ceiling association.
C. Water-reducing admixtures
NOTE:
• ASTM C494, Type A
• Amount used shall be consistent with manufacturer’s
recommendations.
• Use only products approved by the NWCB and/or
regional wall and
ceiling association.
D. Accelerating admixtures
NOTE:
• ASTM C494, Type C and E.
• Must be non-chloride or chloride with rust-inhibitors.
• Amount used shall be consistent with manufacturer’s
recommendations.
• Use only products approved by the NWCB and/or
regional wall and
ceiling association.
E. Pump-aid admixtures
NOTE:
• Amount used to be consistent with manufacturer’s
recommendations.
• Use only products approved by the NWCB and/or
regional wall and
ceiling association.
2.14 Coloring
Compounds for Job-site Stucco Finish
NOTE:
• Delete if not required.
• “A” prepackaged colors recommended
rather than “B” raw color
pigments.
A. Prepackaged colors
NOTE:
• ASTM C979
• Use only coloring compounds manufactured for
a job-site stucco finish.
• Identify manufacturer, brand name and color code.
• Mix with finish coat materials according to manufacturer’s
recommen-dations.
• Best color uniformity can be achieved with prepackaged
products.
B. Raw Color Pigments
NOTE:
• ASTM C979
• Natural or synthetic iron oxides
• Identify manufacturer, brand name and color code.
• Mix with finish coat materials in proportions
which replicate a
previously approved sample.
• Variation in the uniformity of color is normal
when raw pigments are used.
2.15 Mix Proportions
NOTE:
• Proportions are parts by volume for basecoats
and job-site stucco finish
coat.
• Use standard measuring devices and know volumes
for all materials.
• Sequential batches to be proportionally alike.
• All mixing in a mechanical mixer.
• Continue to mix for 3-5 minutes after all ingredients
have been added.
• Add fibers 2-3 minutes before mixing is complete.
• Factory-prepared stucco finish coat per manufacturer’s
requirements.
• Admixtures per manufacturer’s requirements.
• Cement materials shall be based on full bag increments.
• Shovel count can be used for measuring sand if
standardized first.
• Use enough water to produce suitably plastic
cementitious material,
keeping water to a minimum.
• Sequence of materials: (1)
water, (2) half of sand,
(3) all of the cement
and/or lime, (4) balance
of sand and (5) water for
workability.
• “Brown” coat may contain the higher
volume of sand.
• For integral color finish, factory-prepared finishes
will result in truer
and more consistent color.
• Sand per sum of cementitious material.
• For mix no. 1, 3, 4 and 5, volume of sand in
first coat shall the same or
less than volume in the second (brown)
coat, not to exceed 4 parts of
sand per sum of cementitious materials.
• For mix no. 2, volume of sand in first coat shall
be the same or less than
volume in the second (brown)
coat, not to exceed 3 1/2 parts of sand per
sum of cementitious materials.
• Amount of fibers per mix per manufacturer’s
recommendations.
A. Basecoat mix parts by volume
(ASTM C 926) and finish coat mix parts by volume
(ASTM C926)
NOTE:
• Select one of the five mixes or another approved
ASTM C926 mix for the
project. Do not interchange components. Once project
has been started,
do not switch to another mix.
• Architect to indicate which one of the five mixes
to use. If mix is not
shown in construction documents, plastering contractor
may use one of
the five mixes shown in this Guide Specification.
• Delete mixes not to be used in the project.
• Volume of sand per sum of cementitious material.
Mix No. 1—Basecoat
Portland cement .............................. 1
Masonry cement ............................. 1
Sand ............................................ 3
1/2 - 4 1/2
Fibers ............................................
per manufacturer’s recommendations
Mix No. 2—Basecoat
Portland cement .............................. 1
Lime ............................................ 1/4
- 1/2
Sand ............................................ 3-4
Fibers ............................................
per manufacturer’s recommendations
Mix No. 3—Basecoat
1-P portland cement ........................ 1
Masonry cement ............................. 1
Sand ............................................ 3
1/2 - 4 1/2
Fibers ............................................
per manufacturer’s recommendations
Mix No. 4—Basecoat
Plastic cement ................................. 1
Sand ............................................ 3
1/2 - 4 1/2
Fibers ............................................
per manufacturer’s recommendations
Mix No. 5—Basecoat
Portland cement .............................. 1
Plastic cement ................................. 1
Sand ............................................ 3
1/2 - 4 1/2
Fibers ............................................
per manufacturer’s recommendations
B. Job-site stucco finish
coat
White portland cement.................... 1
(or regular portland cement)
Lime ............................................ 1
- 2
Sand ............................................ 3
NOTE:
• Add manufactured coloring compounds to job-site
stucco finish mix per
manufacturer’s recommendations.
• Delete if not applicable.
C. Manufactured stucco
finish
NOTE:
• Mix and apply per manufacturer’s recommendation.
• Manufacturer to be approved by NWCB and/or regional
wall and ceiling.
2.16 Acrylic Finish
NOTE:
• A proprietary finish material by EIFS manufacturer,
approved by NWCB
and/or regional wall and ceiling association.
• 100-percent acrylic polymer material in finish.
• Mix and apply per manufacturer’s recommendations.
• Delete if not applicable.
3.01 Examination
A. Prior to starting lathing
or plastering work, carefully inspect installed work
of other
trades to verify that work is complete to the point
where work of this section may
properly commence.
B. Notify the architect
or proper authorities in writing of conditions detrimental
to the
proper and timely completion of the lathing and/or plastering
work.
C. Do not begin installation
until all unsatisfactory conditions are resolved.
D. A pre-construction
meeting is recommended with the architect and/or owner,
primary
contractor and representatives responsible for the windows,
framing, flashing, roofing,
sealants, stucco and any other building components interfacing
with the stucco.
NOTE:
• The examination of conditions is the responsibility
of all parties involved
in the project.
3.02 Performance
A. The work shall
be performed by a skilled and trained work crew.
NOTE:
• Work shall be performed to create a rigid, secure,
level or plumb finish
surface, with line dimensions and/or contours as indicated
in reference
standards or project documents.
B. Install specified
products and/or systems in accordance with reference
standards,
manufacturer’s recommendations and this Stucco
Resource Guide, unless indicated
otherwise in project documents.
C. Flashings shall be
installed prior to start of lathing or may be required
to be
integrated at the time of lathing. Flashing is not the
scope of work of the contractor
responsible for the stucco assembly.
3.03 Installation of Stucco
Trim Accessories
NOTE:
• Refer to details and other portions of this Stucco
Resource Guide for
additional information
A. Verify that substrate
and work by other trades are complete to the point at
which
installation of trim accessories may properly commence.
NOTE:
• Do not begin work until unsatisfactory conditions
are resolved.
B. Attachments shall be
firm enough to hold trim accessories in place without
misalignment during plastering.
NOTE:
• Flanges or attachment points of trim accessories
shall be secured
to substrate in accordance with requirements of manufacturers
of
approved fasteners. Space per manufacturer’s directions.
• It is recommended that PVC or aluminum reveals,
when used in
conjunction with 2-inch x 2-inch welded wire lath, incorporate
a strip of
expanded metal lath over the solid reveal flanges.
C. It is recommended
that trim accessories have a small top flange “lip”
that goes over
the stucco and/or flange that embeds into the stucco.
D. Zinc alloy or PVC is
recommended if trim accessories are exposed to a high-salt
environment.
E. Install individual
trim-accessory sections to each other at end joints
for accurate
alignment.
F. Install trim accessories
in a manner that ensures a true, level and plumb stucco
surface, and moisture resistant.
NOTE:
• Accurate alignment of trim accessories may require
shimming, limited to
the thickness of stucco.
• Sections of flashing or trim accessories that
butt each other (at corners
or another condition) need to be lapped, caulked,
or have a strip of self-adhering
membrane over the joints. This is to prevent moisture
from
getting to the building structure.
G. Install the trim accessories
in accordance with the required thickness of stucco
basecoat and finish coat requirements. (Refer
to Plaster Thickness section)
NOTE:
• Depth (grounds)
of trim accessory to be in accordance with the
thickness of stucco. (Refer to
Plaster Thickness Tables)
For example, 3/4-inch (19-mm)
stucco requires a minimum ground of a
casing bead to be 3/4 inch (19
mm).
H. Install the longest
possible lengths of trim accessories. A minimum continuous
section (length) of 7 feet
(2 m) is recommended.
3.04 Trim Accessory Joints
NOTE:
• Installation to be in accordance with section
3.03—Installation of
Stucco Trim Accessories.
• Trim accessory joints refer to various types:
control joints, expansion
joints, reveals, and/or any other devices or systems
that divide (break) the
stucco membrane surface.
• Architect is to select the type of joint and
indicate on drawing the
location of joints.
• Trim accessory joints provide relief of stresses
from the structure and
cement-plaster curing process.
• Trim accessory joints provide for a plaster stop
and a screed.
• Aluminum and/or PVC reveals require that when
the lath is installed
over the flange, it totally covers it. The welded wire
and woven wire lath
shall be installed so as the crotch of the lath is over
the flange.
• It is recommended that PVC or aluminum reveals,
when used in
conjunction with 2-inch x 2-inch welded wire lath, incorporate
a strip of
expanded metal lath over the reveal flanges.
A. The water-resistant
barrier must continue unbroken behind trim accessory
joints in
vertical or horizontal direction.
B. Locate to trim accessory
joints strategically at points where building movement
is
anticipated.
1. Wall penetrations
2. Structural plate lines
3. Junctures of dissimilar
substrates
4. Existing construction
joints in structure
5. Columns
6. Cantilevered areas
C. Joints are recommended
in stucco assemblies with lath reinforcement but have
limited use in direct-applied stucco over concrete or
concrete masonry surface.
D. It is recommended that
trim accessory joints be weather-sealed by embedment
in
caulking at intersections when placed end-to-end and
at the terminations.
E. It is recommended to
install vertical joints continuously and to abut horizontal
joints
to vertical (be sure that water-resistant
barrier runs continuously behind joints).
NOTE:
• The use of horizontal reveals, flashing designs
and/or other horizontal
surface breaks may prevent continuous vertical joints.
• Expansion joints govern over control joints.
F. Install longest possible
lengths. No termination of a section within 24 inches
(600
mm) of an intersection, with the exception of
pre-manufactured trim accessory joint
intersections.
G. It is recommended
that trim accessory joints be installed on framed, sheathed
construction so as to create stucco panel of 150 to
180 square feet (14 m 2 to 17
m 2 )
in as square a configuration as possible.
NOTE:
• Maximum recommended length of a panel is 18 feet
(5.5 m). Panel size
approximately 3-to-1 ratio.
H. It is recommended
that trim accessory joints be installed with concrete
or concrete
masonry construction so as to create a stucco assembly
(with lath reinforcement)
of
200 to 250 square feet (18 m 2
to 23 m 2 ).
I. Installing control
joints over continuous lath is an approved method.
NOTE:
• Control joint is a one-piece trim accessory.
• Control joint may be installed in the “field
of panel” only if there is
framing or wood sheathing continuous substrate behind
it for attachment.
• Control joints to be wire tied to lath with 18-gauge
tie wire (recom-mended
method when lath goes over sheathing board other than
wood).
J. The recommendation
for the installation of expansion joints or reveals
is to break the
lath and lap it over on top of each of the flanges.
NOTE:
• Control joints may also serve as expansion joints,
if so specified and
detailed.
• Expansion joints and/or reveals may consist of
one or two pieces.
• Control joints are limited in their degree of
movement. Two-piece
expansion joints provide greater movement.
K. Sheathed framed construction
with vertical trim accessory joints that require the
lath
to be terminated (cut)
and installed on top of the flanges shall be placed
at framing
member locations. Lath shall be attached with appropriate
fasteners through the
trim accessory flange, sheathing and into the framing
member.
NOTE:
• The lath/flange on each side of the trim accessory
joint to be attached to
a framing member. Double framing supports would be required
at these
locations.
• This condition does not pertain to control joints
installed over continu-ous
lath.
3.05 Lathing for Soffits
A. Suspended soffits/ceilings
shall be erected so that the finished basecoat cement
plaster surface is true to line and level, with allowable
tolerance of 1/4 inch (6 mm)
in 10 feet (3.1 m)
NOTE:
• Construction documents shall indicate the approximate
amount of
deflection of structure to which suspended soffit is
attached..34 Northwest
• No attachment of soffit/ceiling abutting to walls
or fascia (in order to
prevent transfer of stresses).
• Vertical compression struts to withstand upward
wind pressures are not
required unless indicated in project documents.
• NWCB recommends a soffit framing system with
sheathing (refer to
3.06-B) because it incorporates a gypsum sheathing
board attached to
furring “hat” channels. This type of assembly
produces a better stucco
soffit. The sheathing board provides rigidity to the
framing system and
helps produce a uniform stucco thickness.
• Refer to sections 3.03 and 3.04.
B. Spacing, attachment,
size and type of hangers, fasteners and inserts shall
be as
required in reference standards in section 1.04.
NOTE:
• Fasteners and inserts shall have up-to-date testing
information from
manufacturers.
3.06 Lathing Systems
for Suspended Soffits (for details,
see soffit section)
NOTE:
• For additional suspended soffit configurations
(size, spans and spacing),
refer to reference standards in section 1.04.
(ASTM C1063)
• Construction documents to indicate either the
soffit framing system
(refer to 3.06 A) or soffit
framing system with sheathing (refer
to 3.06 B).
A. Soffit framing system
1. Hanger wires maximum
support 16 square feet (1.5 m
2 )
2. 1 1/2-inch
(38-mm) main runner channels o.c. spacing 48
inches (1.2 m)
3. 3/4-inch (19-mm)
cross-furring channels o.c. spacing 13 to 16 inches
(325 to
400 mm)
4. 3.4-pound-per-square-yard
diamond-mesh lath
5. Wire-tie lath to cross-furring
channels with 18-gauge tie-wire, 6 inches (150
mm) o.c.
B. Soffit framing system
with sheathing
1. Hanger wires, maximum
support 16 square feet (1.5 m
2 )
2. 1 1/2-inch (38-mm)
main runner channels, maximum o.c. spacing 48 inches
(1.2 m)
3. 20-gauge furring “hat”
channels, spaced maximum 16 inches (400
mm)
4. 1/2-inch (13-mm)
gypsum sheathing board
5. 3.4-pound-per-square-yard
self-furring diamond-mesh lath attached through
gypsum sheathing board into furring channels, maximum
6 inches (150 mm)
o.c. with type S screws—wafer head—1 inch
(25 mm) long.35 Northwest
3.07 Soffit Lathing System to
Wood Joist
A. 3/8 inch (10 mm) rib
lath attached 6 inches (150 mm)
o.c., with one of the following:
1. Roofing nails: 11
gauge • 7/16-inch diameter head • 1-inch long
2. Staples: 16 gauge •
3/4-inch crown • 1 1/4-inch long
3. Screws: type W •
wafer head • 1-inch long
NOTE:
• Fasteners must penetrate into the wood a minimum
of 3/4 inch (19 mm)
both legs of staple must penetrate wood. Fasteners to
be centered,
minimum 3/8 inch (10 mm) from edge of wood joist.
• Maximum spacing of wood joist 24 inches (600
mm) o.c.
3.08 Application of Stucco Basecoat
for Soffits
NOTE:
• Do not use the double-back method of applying
the basecoats.
• Verify trim accessories and lath are installed
so as to provide proper
screeds, thickness and alignment for plastering.
• Do not begin plastering work until unsatisfactory
conditions are resolved.
• Cement plaster can be applied by trowel or machine.
• Apply basecoat to entire horizontal surface and/or
section without
interruption or “cold joints.”
A. Indicate the permissible
mix number and its proportions to be used for the basecoat
NOTE:
• Delete basecoat mixes not applicable to this
project.
• Do not change selected mix or proportions after
plastering operation has
started.
• Measurement of ingredients (materials
of the mix) to be done with
devices of known volume, accurate, and successive batches
proportion-ally
alike.
• Use only enough mix water to make plaster a workable
consistency.
• Admixtures to be submitted for approval.
• Basecoat admixtures designed for improving the
mix or for enhancing the
plaster application must have been manufactured strictly
for that
purpose.
• Admixtures must be accurately measured and used
only in accordance
with manufacturer’s recommendations.
B. Apply stucco first
(“scratch”) coat in a nominal thickness
of 3/8 inch (10 mm). First
coat to completely embed the lath. First coat to be
thick enough to allow for scoring
of cement plaster surface. (Refer
to Plaster Thickness Tables)
NOTE:
• Scoring of the first coat should be uniform and
shallow, approximately 1/
8 inch (3 mm).
C. Moist cure the first (“scratch”)
coat for a minimum of 48 hours before application of
the second (“brown”)
coat.
NOTE:
• First coat to be hard and rigid before receiving
the second coat.
D. Apply stucco second
(“brown”) coat
in a nominal thickness of 3/8 inch (10
mm)
over stucco first coat. Second coat thickness to bring
the combined basecoats (first
and second) thickness to a nominal thickness
of 3/4 inch (19 mm). (Refer to
Plaster
Thickness Tables)
NOTE:
• Apply second coat over a damp first coat. If
required, apply a fine spray
of clean water, so as to dampen only. Do not saturate.
Allow water
sheen to disappear before applying the second coat.
E. Apply the second coat
with sufficient material and pressure to ensure a tight
uniform
bond to the first coat.
NOTE:
• Apply second coat so as not to deform or crack
the first coat.
F. Rod the second coat
to a true, even plane, filling surface defects with
cement plaster.
G. Trowel-float the second
coat surface uniformly.
NOTE:
• The floating process densifies the basecoat and
provides a proper surface
for the finish coat application.
• Float the basecoat after it has set and when
moisture is still present in it.
• Floating the basecoat that is to receive an acrylic
finish coat is critical
because of the thickness of this finish.
3.09 Curing of Soffit Basecoat—Refer
to section 3.40.
NOTE:
• After the second coat has been applied, moist
cure it as required, and then
wait a minimum of seven days before the start of finish
coat application.
3.10 Stucco Finish Coat—Refer to section 3.41.
3.11 Acrylic Finish Coat—Refer to section 3.42.
3.12 Additional Types of Finishes—Refer to section
3.43.
3.13 Cement Plaster Direct to Concrete
NOTE:
• Concrete to be cured for a minimum of 28 days..37
Northwest
• Not recommended for horizontal surfaces (other
than ceilings/soffits).
• Concrete surface to be straight and true, in
accordance with standards.
• Concrete surface to be clean, no form release
agents, no curing compounds
or other elements in concrete surface preventing a proper
bond.
• Concrete should be in good condition and have
uniform absorption rate
over entire surface.
• Concrete in poor condition (spalling, delamination,
voids) or other
surface defects requires repair before plastering.
• If the concrete surface is not in proper condition,
self-furring lath must
be installed.
• If there is any concern about the bondability
of the cement plaster direct
to concrete, a test area is recommended. Apply 1/4”
- 1/2” thick, by 1’x1’
of cement plaster basecoat to concrete; let it cure
for 3 - 4 days. Then try
to remove it. Do this type of test at more than one
location.
• Acrylic finish coat is not recommended for concrete
retaining walls.
3.14 Stucco “Finish Coat” Direct to Concrete—Refer
to “Stucco Wall Assemblies” section
detail A6 in this Stucco Resource Guide.
NOTE:
• The finish coat over concrete is used to enhance
the surface appearance;
it is not designed to “true up” the surface.
• Smooth troweled stucco finishes are not recommended
because of the
possibility of very fine map cracking. If smooth troweled
finish is specified,
surface should be painted with a high-quality acrylic
exterior paint.
A. Apply liquid bonding
agent directly to concrete surface in accordance with
the
recommendation of manufacturer of the material.
B. Application of the
stucco finish coat—Refer to section 3.41.
3.15 Acrylic Finish Coat
Direct to Concrete—Refer to section 3.42.
NOTE:
• Do not apply finish until all irregularities
on the concrete surface have
been corrected.
3.16 Two Coat Stucco Direct
to Concrete—Refer
to “Stucco Wall Assemblies” section
detail A7 in this Stucco Resource Guide.
NOTE:
• This method provides for an economical way of
creating an acceptable
level finished wall surface.
• The system provides a leveling basecoat (brown
coat) over the concrete
surface and makes a suitable base for the finish coat
with limited total
stucco thickness of 1/2 inch (13
mm).
• Refer to section 3.13..38 Northwest
A. Apply liquid bonding
agent directly to concrete surface only in accordance
with the
recommendation of manufacturer of the material.
B. Install trim accessories—termination
trim accessory, corner reinforcements (corner
beads), trim accessory joints (control joints) and other
specified accessories in
accordance with sections 3.03 and 3.04.
NOTE:
• Install per related detail sections of this Stucco
Resource Guide.
• Delete trim accessories no | 
