The following document is based on the 2010 FBC, FBCR, ASTM C926, ASTM C1063, and other Click Application Guides regarding Stucco installation, procedures and practices. This document is not all inclusive and does not cover all the requirements for compliant installation of stucco. This document is meant to be used as a guide to address some of the common installation and proper application issues found during field inspections.
Stucco Installation Over Masonry:
Conventional stucco over masonry surfaces may be applied with two or three coats. Two-coat systems over masonry consist of: first coat = 3/8 inch thick and finish coat = 1/8 inch thick; or over cast concrete consist of: first coat = 1/4 inch thick and finish coat = 1/8 inch thick. Three-coat systems consist of: first coat = 1/4 inch thick, second coat = 1/4 inch thick, and finish coat = 1/8 inch thick over both masonry and cast concrete.
When required by ASTM C 926, Section 5.2.2; an exterior bonding agent, conforming to ASTM C 932, shall be used on all masonry surfaces. In lieu of a bonding agent, a dash coat, roughing the surface, or metal lath are also acceptable methods for bonding.
FBC 2510.3 Installation, references ASTM C 926 requires form ties or other obstructions (including masonry cut nails for clean out opening forms) to be removed or trimmed back even with the surface of the solid base. In addition, if the nails are to be trimmed flush and left in place, they need to be corrosion resistant as would be required for lath or other metal accessories, ASTM C 926 section 5.2 and C 1063 section 6.
Stucco Installation Over Wood:
Conventional stucco over wood should always be applied as a three-coat system. Scratch coat =3/8 inch thick, brown coat =3/8 inch thick, and finish coat =1/8 inch thick. The scratch coat must be scored horizontally on vertical surfaces. Successive coats should be applied as soon as possible after the underlying coat has sufficient strength and rigidity to resist damage when the next coat is applied. A mist cure shall be maintained as needed for climatic conditions.
Where structural wood panels are used for sheathing, a minimum 1/8 inch separation shall be provided.
The weather resistant barrier (WRB) must be installed per Sections R703.6.3 of the Florida Building Code Residential and 1404.2.1 of the Florida Building Code. Where cement plaster (stucco) is to be applied to lath over frame construction, measures shall be taken to prevent bonding between the cement plaster and the water resistive barrier. A bond break shall be provided between the water resistive barrier and the cement plaster (stucco) consisting of one of the following:
Two layers of an approved water resistant barrier material, or
One layer of an approved water resistant barrier over an approved plastic house wrap, or
Other approved methods or materials applied in accordance with the manufacturer’s installation instructions.
Lathing shall be connected to the framing members 7 inches on center. Lath shall be attached to horizontal wood framing members with 1.5 inch roofing nails and to vertical wood framing members with 6d common nails or 1 inch roofing nails driven to penetration of not less than ¾ inch, or 1 inch wire staples driven flush with the plaster base. Staples shall have crowns not less than ¾ inch and shall engage not less than three strands of lath and penetrate the wood framing members not less than ¾ inch. The fasteners must penetrate the wood framing members not less than 3/4 inch and not be installed randomly in the wall sheathing.
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