Plaster makes a smooth, hard finish on walls that can accept paint or wallpaper without cracking. It has been in use far longer than drywall. If you live in an older home with plaster walls that need repairs or would like to install new plaster walls, you must know what lies beneath a plaster coating.
Lath
Older homes with plaster walls usually have small strips of wood called laths under the plaster. Laths commonly were cut from cedar, according to the Sound Home website, and were attached to a wall's framing. This provided a smooth and sturdy surface to hold a plaster finish. If your home's laths are in good condition and the plaster walls are intact, there is no particular reason for replacing this system. Repairing broken or rotten laths is difficult. Installing a new plaster veneer system is a better option.
Blueboard
Modern plaster veneer systems use a special type of gypsum board known as blueboard. Blueboard is named after the special waterproof paper used over the gypsum core, according to This Old House. Without this coating, the board would retain moisture in the plaster and crumble. Blueboard is basically drywall with better water resistance. However, drywall should not be used underneath a plaster layer because it will be damaged by moisture absorption and isn't designed to support the weight of a plaster finish.
Metal Laths
While wooden laths are rarely used in modern plaster wall applications, special finishing pieces known as metal laths still play an important role. These pieces of mesh are installed between boards of gypsum backer and in corners to prevent plaster from seeping into the cracks, according to National Gypsum. Metal lathes support the gypsum board and prevent plaster from cracking by keeping the boards from moving when light pressure is applied.
Considerations
Hanging blueboard sheets and metal laths saves time and effort instead of nailing in hundreds of small strips of wood. However, there are a few situations when a traditional wooden lath system is preferred. Repairing a plaster and lath system preserves the historical value of an older home. Plaster over wood also offers a different acoustical condition than gypsum board backing, according to Sound Home. A few special decorative wall effects are only possible with a wooden lath system as well.
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