Stucco and EIFS
Traditional stucco is a cementations exterior plaster coating available in a wide range of colors and textures. Its characteristics are similar to concrete in that stucco is porous, it shrinks and cracks; however, it has high impact resistance. On masonry substrate, we have the application of two coats and three coats to the metal lathe. With its variety of colors and textures, stucco continues to be one of the most popular wall finish systems. Stucco systems shed water because concrete has a drainage plane. This drainage capability is provided by building paper installed shingle ¬fashion over the exterior sheathing and under the metal lath. The paper breathes, allowing water vapor to escape.
EIFS is a cladding technique designed to protect and insulate buildings while reducing energy costs through a particular layering process, starting inside the building and extending to the outer wall. The EIFS process insulates while preventing moisture build-up within the system. It utilizes rigid insulation boards on the exterior of the wall sheathing with a plaster appearance exterior skin. EIFS wall system is available in two types: a barrier wall system or a wall drainage system;
– Barrier EIFS wall systems rely primarily on the base coat portion of the exterior skin to resist water penetration. Therefore, all other components of the exterior wall must either be barrier type systems or be appropriately sealed and flashed to prevent water from migrating behind the EIFS and into the underlying walls or interiors.
– Wall drainage EIFS systems are similar to cavity walls; the installation is over a weather barrier behind the insulation that acts as a secondary drainage plane. The weather barrier must be properly flashed and coordinated with all other portions of the exterior wall to prevent water from migrating into the underlying walls or interiors. EIFS with drainage typically consists of the following components:
- An optional water-resistive barrier (WRB) that covers the substrate
- A drainage plane between the WRB and the insulation board
- Insulation board typically made of expanded polystyrene (EPS) which is secured with an adhesive or mechanically to the substrate
- A water-resistant base coat
- Glass-fiber reinforcing mesh embedded in the base coat
- A finish coat that typically uses colorfast and crack-resistant acrylic co-polymer technology.
For stuccos attach two layers of Grade D, waterproof building paper using galvanized nails or staples in a shingled fashion over the wall sheathing extending 16 inches around all corners. Install trim accessories (to protect the exposed stucco and to provide clean finished lines), casing beads, a galvanized, self-furring, expanded metal lath or 1” woven wire stucco netting over the entire surface also extending 16 inches around all corners. Create wall panels keeping them as square as possible as you place wall expansion joints. Mix the base coat stucco to a workable consistency – when the stucco will “hang” on a trowel held at a 90-degree angle. Then, apply the base coat stucco using a square trowel held at a 45-degree angle. Use firm trowel pressure to force the stucco into the lath. Work from the bottom of the wall up and apply at a thickness of about 3/8 inch over the entire area. Screed the stucco to a uniform depth of 3/8 inch using a straight edge. Scratch 1/8 inch deep horizontal grooves into the base coat with a raking tool once the stucco has become thumb-print hard, cure the scratch coat for 24 to 48 hours. Mix and apply another 3/8 inch layer of base coat stucco directly to the scratch coat. Screed the surface using a straight board or darby to 3/8 inch thickness and fill any surface voids with an additional base coat. The total combined basecoat depth should be 3/4 of an inch thick. Apply a Finish Coat Stucco in the preferred application working from the bottom of the wall to the top. Complete the entire wall in one form as you fill all control joints, expansion joints, and gaps
To focus only on EIFS or stucco without reviewing the wall system as an assembly is to assume that each product in the wall operates independently. Indeed, there is a symbiosis between products such as sheathing, EIFS or stucco, windows, flashings, and sealants. The installation of all of these must be correct for the wall system to function efficiently.