This post is intended to provides some clarity regarding the differences between drywall and plaster. Following are some definitions and comparisons between the two options.
Drywall
Drywall, also commonly called wallboard, plaster board or sheetrock (sheetrock is a brand name) was developed as an alternative to a lath and plaster system. Drywall is made by compressing air-entrained gypsum plaster into a panel. The panels are faced with paper or fiberglass.
Lath and plaster.
For a lath and plaster installation thin strips of wood, called lath, are installed perpendicular to the framing of the home. (shown in figure 1). Gaps are left between the lath, so that some of the plaster pushes through the gaps and slumps over the back side, forming a mechanical bond when it sets.
Fig. 1.
Joint Compound
Joint compound is made from gypsum, water and various bonding agents among other things. Joint compound is applied, with paper or vinyl mesh tape to the joints between drywall panels. Multiple layers of joint compound are applied and sanded smooth to create an even wall surface. (Shown in figure 2)
Fig. 2.
Plaster
The most common types of plaster to find in the U.S. are Gypsum plaster and Portland Cement based plaster, although lime plaster, clay plaster, and other earthen plasters are used as well. Unlike joint compound which hardens as a result of drying, plaster hardens as a result of a chemical reaction which is initiated by adding water to the dry plaster powder. Modern plaster installations use a gypsum wallboard referred to as “blue board”.
Cracking Plaster
A lot of people have a negative opinion of plaster because they’ve experienced issues with cracking or de-lamination. Defects that occur in plaster are almost always a result of the home shifting over time or a bad plaster mixture. Due to the standardization of Building products, consistency in the plaster mixture is no longer an issue. Home shifting is addressed below:
Many people have observed that homes with drywall for the wall covering, even if they are old, have less of a problem with cracking walls and ceilings than homes with plaster walls. This is usually attributed to the plaster itself. What’s really going on here however is that around the same time that drywall began being installed on the interior of our homes, plywood was beginning to be installed to the exterior of homes beneath the siding. Plywood is a very dimensionally stable product that keeps the framing of a home from racking. (shown in figure 3) Which is one of the most common reasons for plaster to crack. By keeping the walls from shifting plywood sheeting keeps the plaster from cracking.
Fig. 3.
Plaster Vs. drywall
Plaster offers many advantages over a typical drywall installation. Drywall and the joint compound that conceals the joints are relatively soft and susceptible to damage. Drywall can be gouged simply by using one’s thumbnail. Plaster on the other hand gets spread over the entire surface of the wallboard and sets up to create a very hard and durable surface.
Plaster is also a more pure product that uses less man-made chemicals. Really the only down side to plaster is the cost. The materials cost more and plaster application requires more skill and demands higher labor rates.
One of the benefits of plaster, particularly in the context of a remodel, is that it does not require sanding to achieve a smooth surface which cuts down on job-site dust significantly.
I hope this provides you with some more clarity. If you have further questions they can be asked by submitting a form on our FAQs page: www.portlandtradesmen.com/faqs