Masonry Magazine June 2008 Page. 39
Wond Beam Detail
Joist Bearing Detail
Image courtesy ofercon Florida
Image courtesy of AeroFlorida
There is generally no need to level the surface, and horizontal and vertical joints may be chamfered as an architectural feature, or may be filled.
Masonry veneer may be used over AAC masonry in much the same way that it is used over other materials. The veneer is attached to the AAC masonry wall using special masonry ties. The space between the AAC, and the masonry can be left open (forming a drainage wall), or can be filled with mortar.
When AAC panels are used in contact with moist or saturated soil (for example, in basement walls), the surface in contact with the soil should be coated with a waterproof material or membrane. The interior surface should either remain uncoated, or be coated with a vapor-permeable interior finish.
Interior finishes for AAC masonry
INTERIOR FINISHES are used to enhance the aesthetics and durability of AAC. They should be compatible with the underlying AAC in terms of thermal expansion and modulus of elasticity, and should be vapor permeable.
Many different types of interior finishes are available. Interior AAC wall panels may have a thin coat of a mineral-based plaster to achieve a smooth finished surface. Lightweight interior gypsum-based plaster may provide a thicker coating to level and straighten walls, and to provide a base for decorative interior paints or wall finishes.
Interior plasters have bonding agents to enhance their adhesion and flexibility, and are commonly installed by either spraying or troweling.
When applied to the interior surface of exterior AAC walls, gypsum board should be attached using pressure-treated furring strips. When applied to interior walls, moisture-resistant gypsum board can be applied directly to the AAC surface.
For commercial applications requiring high durability and low maintenance, acrylic-based coatings are often used. Some contain aggregates to enhance abrasion resistance.
When ceramic wall tile is to be applied over AAC, surface preparation is normally necessary only when the AAC surface requires leveling. In such cases, a Portland cement- or gypsum-based parge coat is applied to the AAC surface before setting the ceramic tile. The ceramic tile should then be adhered to the parged wall using either a cement-based thin-set mortar or an organic adhesive. In moist areas such as showers, only a Portland cement-based parge coat should be used, and the ceramic tile should be set with cement-based, thin-set mortar only.
Typical construction details for AAC elements
A WIDE RANGE of construction details for AAC masonry is available on the Web sites of individual manufacturers, accessible through the Web site of the AACPA. IMAS
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Richard E. Klingner is the L. P. Gilvin professor of civil engineering at the University of Texas at Austin, where he specializes in the behavior and design of masonry, particularly for earthquake loads. The opinions expressed in this article are his own, and do not necessarily reflect the official viewpoint of the MSJC or its sponsoring societies. Contact him at klingner@mail.utexas.edu.
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June 2008
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