GUIDE SPECIFICATION

 

LATH, PORTLAND CEMENT PLASTER AND PRESWITT QUALITY ACRYLIC FINISH

PART 1 GENERAL

1.1 Scope:

Guide specifications for the minimum requirements for the system and application of fiber reinforced Portland cement plaster (stucco) with Preswitt Quality Acrylic Finish.

1.2 The contractor shall provide all materials, labour and equipment necessary to complete this system of Portland cement plaster as shown on drawings and/or as described herein.

1.3 Flashing, caulking, sealants, sealers, shall be furnished and installed by others.

1.4 Standards:

Workmanship and installation shall be performed per AWCC Standards Manual Specification in accordance with the Building Codes and manufacturer's printed instructions.

1.5 Qualifications:

The contractor must be qualified in the workmanship of plastering. Must be able to show completed work of equal scope.

1.6 Submittals:

The contractor shall supply mock-up finish samples.

A. Do not proceed with lathing or plastering until all products and finish samples are approved, if required.

1.7 Be prepared for a pre-job meeting with the architect, owner, general contractor, and manufacturer before the start of lathing and plastering proceeds.

1.8 Materials:

To be delivered to job in original containers with labels intact and legible.

A. Storage and protection of all products are the responsibility of the contractor performing the scope of the work.

1.9 Job Conditions/Environmental Requirements for Cement Plaster:

A. Cold Weather

1. Do not use frozen material.

2. Do not apply cement plaster to frozen surfaces or surfaces containing frost.

3. Do not mix materials or apply cement plaster when ambient temperature is less than 35°F/1.6°C.

B. Hot Weather

1. Protect cement plaster from uneven and excessive evaporation during hot, windy, and dry weather.

2. Moist cure after each coat of cement plaster with water if ambient temperature is more than 75°/24°C. Moist cure for 48 hours after application of coats.

3. On hot, dry, or windy days the cement plaster should be moistened down and then covered with a single sheet of polyethylene plastic.

4. Moist curing is required at the start and end of the work day.

5. When the humidity is higher than 75% moist curing is not required.

1.10 Double Back Method:

Whereby the scratch and brown coats are applied and cured as one system is approved.

A. The second coat (brown) should be applied as soon as the first coat is rigid.

1.11 Job Conditions/Environmental Requirements for Acrylic Finish:

A. Do not use Acrylic Finish materials if they have been frozen.

B. Do not apply Acrylic Finish when ambient temperature is less than 40°F/4.4°C.

C. Do not apply Acrylic Finish unless the temperature has been 40°F/4.4°C for at least 24 hours before application.

D. Cold Weather:If heating and tenting is required to perform the application of the Acrylic Finish coat, it is not the responsibility of the Acrylic Finish contractor to provide it.

E. Do not apply Finish coat when there is any form of precipitation.

F. Protect cement plaster from all forms of precipitation during the application and the setting/curing period of the finish coat. Ensure that the Finish is fully set prior to removing protective coating.

G. Do not apply Finish coat to Basecoat of cement plaster if sun is directly on the wall surface and temperature is 75°F/24°C. Work in the shade whenever possible.

1.12 Control Joints:

A. It is not required to cut lath behind control joints if flanges of control joint is designed to give a good key to the cement plaster.

B. Panels should be relatively square.

C. No area should exceed 18 lineal feet in length without a control joint.

D. Install control joints for surface areas of approximately 150 square feet.

E. Install control joints where dissimilar back-up materials join.

F. Control joints are recommended at surface penetrations, (windows, doors, etc.) and at areas of structural stress.

PART 2 MATERIALS/PRODUCTS

2.1 Building Paper:

Sheathing paper shall be water repellent breather type membrane conforming to CAN2-51.32M77 "Sheathing membrane breather type."

2.2 Lath:

A. Expanded Metal Lath.

B. Woven Wire Lath: 17 gauge 1½" mesh.

C. Welded Wire Lath: 16 gauge.

D. Rib Lath.

2.3 Accessories:

A. Shapes used as grounds, sized and dimensioned to provide for required plaster thickness.

B. All accessories manufactured of galvanized steel, zinc, aluminum, or plastic materials.

C. Configuration of casing beads and control joints to provide lip flange and/or embedment section.

D. Corner beads to be P.V.C. or welded wire.

E. Standard trim items: control joints, casing beads, exterior corner beads, and base screeds.

2.4 Plaster Material:

A. Portland Cement: ASTM C150 Type I or II.

B. Portland Cement & Pozzolanic "Fly Ash": ASTM C150 & ASTM C618.

C. Masonry Cement: ASTM C91.

D. Lime: ASTM C206-Type S.

E. Sand: ASTM C144, type used for cement plaster.

F. Water: Clear and free from substances harmful to plaster.

2.5 Mix General:

A. Accurate proportions of materials for each batch. Measuring devices of known volume for all materials.

B. Size batches for complete use within maximum of one hour after mixing.

C. Withhold 10% mixing of water until mixing is almost complete then add as needed to produce necessary consistency. Keep water to a minimum.

2.6 Mix Proportions by Volume:

Selection of either A, B, or C mix only. Do not inter-mix these three sections or change volume proportions of these sections.

Basecoat PROPORTIONS PARTS BY VOLUME
Stucco Mixes Cementitious Materials Sand (Volume of Sand per Sum of Cementitious Materials)
Symbols Portland Cement Lime Masonry Cement First Coat Second Coat
A 1 0 to 1/4 - 2.5 to 4 3 to 5
B 1 3/4 to 1.5 - 2.5 to 4 3 to 5
C - - 1 2.5 to 4 3 5o 5

STUCCO BASES - PERMISSIBLE MIXES
Mixes for Stucco Coats
Plaster Base First (Scratch) Second (Brown
Low absorption such as dense concrete, dense smooth clay brick, etc. A A
High absorption such as concrete masonry, porous clay brick or tile, etc. B C B C
Metal reinforcements A B C A B C

2.7 Acrylic Finish:

Preswitt Quality Finish.

PART 3 EXECUTION

3.1 Cement Plaster Directly Over A Concrete Surface:

A. Concrete surface must be clean of dust, loose particles, oil, and other foreign matter which would affect a bond of cement plaster to concrete.

B. Apply a liquid bonding agent to concrete surface per manufacturer's standards.

C. Minimum thickness of cement plaster Basecoat 3/8", maximum thickness 5/8".

D. Test bond of cement plaster to concrete surface.

E. Cement plaster must be applied with sufficient force (by hand or machine) to develop full adhesion between plaster and the substrate.

F. Cement plaster Basecoat must be rodded off to a true flat plane. Even and level with screeds. Follow this by wood floating or darbying the surface. Fill all voids and dress surface for Acrylic Finish.

3.2 Cement Plaster Directly Over Masonry Surface:

A. Masonry surfaces must have two coats of cement plaster.

B. Masonry surface to be clean and in condition for a direct bond of cement plaster. Pre-wet the wall before plastering.

C. Cement plaster must be applied with sufficient force (by hand or machine) to develop full adhesion between plaster and the substrate.

D. Apply a ¼" - 3/8" cement plaster Basecoat. Let cure for 48 hours before applying second Basecoat. Rough surface for good bond of second coat.

E. Apply second Basecoat so that total thickness of both coats is ½ to ¾" thick.

F. Cement plaster Basecoat must be rodded off to a true flat plane. Even and level with screeds. Follow this by wood floating or darbying the surface. Fill all voids and dress surface for Acrylic Finish.

3.3 Installation of Lath & Accessories:

A. All items to be attached so that they are level, plumb and true, and create a proper screed and depth for the cement plaster.

B. Attach building paper, lath, and accessories per standards and code.

3.4 Cement Plaster Over Lath:

A. Total thickness of Basecoats to meet code requirements for fire rated construction. (Minimum 7/8" thick for frame construction).

B. Examine wall surface to ensure proper application of lath and accessories.

C. Normal plaster Basecoat thickness:

1. First Coat "Scratch" - 3/8" - ½"

2. Second Coat "Brown" - ¼" - 3/8"

D. Cement plaster must be applied with sufficient force (by hand or machine) to develop full adhesion between plaster and the substrate.

E. First coat to completely embed lath. Cross rake slightly to provide key for second Basecoat. Coat must be uniform in thickness.

F. Second coat applied so that it meets the required total thickness and it must be uniform in its thickness.

G. Second coat of cement plaster must be rodded to the desired thickness and leveled to screeds. Rod off to a true flat plane. Follow this by wood floating or darbying the surface. Fill all voids and dress surface for Acrylic Finish.

H. Completed second coat of cement plaster base to cure for 10-14 days. See general conditions.

3.5 Acrylic Finish Coat:

A. Must be applied continuously and in one operation to the entire wall area.

B. A wet edge must be maintained.

C. Finish to be applied so that there are no scaffold lines or other marks due to the application.

D. The mixing and application must follow the manufacturers recommendations.

E. Texture and color as selected by architect and/or owner.