Elastomeric Adhesives for Field-Gluing Plywood Floors

Twenty elastomeric construction adhesives were evaluated for their suitability in field-gluing plywood flooring to lumber joists. Several were found that should give satisfactory performance under most conditions of installation and service. Average dry shear strengths of individual adhesives varied from 119 to 414 psi, with an overall average of 247 psi after curing for 28 days. Seventy-nine percent of this strength was developed within 14 days, and all adhesives were near full cure within 28 days. Some of these adhesives had only a moderate degree of water resistance. A dry and wet shear strength of 100 psi was arbitrarily established as a minimum strength requirement for adhesives that would be used in the field-glued plywood floor system. Six adhesives met this requirement and were selected for further study. These six adhesives were more tolerant of typical field-gluing conditions than any conventional woodworking adhesives. They bonded the surfaces of dry lumber in varying thicknesses of gluelines at near-freezing temperatures when open assembly time was 20 minutes or less. However, somewhat erratic bonds of lower strength developed on surfaces of wet lumber, particularly at near-freezing temperatures. Overall average shear strength of these six adhesives dropped 34 percent on surfaces of wet lumber and 67 percent on wet lumber when the adhesives were cured at these low temperatures. Without appreciable losses in shear strength, four of these six adhesives withstood extreme cyclic moisture content and dimensional changes in simulated floor sections over a 6-month period. Under such stresses, as well as under mechanically-applied static loads, most of these adhesives were subject to considerable elastic and plastic deformation. At the load levels normally found in residential floors, many high-strength elastomerics should give satisfactory strength and stiffness without excessive deformation. The results of the oxygen-pressure test were inconclusive, primarily because there were no correlation tests with natural long-term aging of adhesive joints. The fact that a number of these adhesives withstood 4 weeks of oxygen-bomb aging, considered by some as equivalent to approximately 20 years of actual service, is an encouraging indication of permanence of properly formulated elastomeric adhesives.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member