Strengthening Plaster Wall Systems

A Portland cement plaster wall system has many positive features, but one of the physical properties that it does not possess is flexural strength. It is because of the inability of the Portland cement plaster membrane to bend or flex that glass fiber strands were used in Portland cementbased plaster. There are various types of synthetic fibers on the market that will provide flexural strength to the plaster matrix The information in this article is focused on research and testing by the Northwest Wall & Ceiling Bureau as it pertains to chopped glass fiber strands in the base coats of Portland cement plaster. There are two types of glass fiber strands; alkaline resistant (A/R) glass fiber and conventional E-glass fibers. Research completed by the concrete industry has shown that E-glass fibers in an alkaline medium will break down after a long period of time. Since the concrete industry was using glass fibers to increase structural properties, it was important to use A/R glass fiber. In our research with Portland cement plaster, we found that conventional E-glass fibers performed well for the purpose intended. Chopped E-glass fibers added to the scratch and brown coats for Portland cement plaster helped eliminate cracking. This is especially important during the early curing process. By Robert C. Drury Executive Director, Northwest Wall and Ceding Bureau