Test results for three representative adhesives were obtained for use in the development of a proposed standard for limited moisture exposure (CSA O112.10). The adhesives tested were an emulsion polymer isocyanate (EPI), a polyurethane (PUR) and a melamine-urea formaldehyde with 40% melamine resin content (MUF40). Currently, EPI and PUR are used for I-joists and fingerjoined lumber. MUF40 was included in the study as a non-conforming adhesive. The range of performance of these adhesives, along with that of melamine formaldehyde (MF) and polyvinyl acetate (PVA) evaluated in a previous study, is baseline information used in defining acceptable performance levels for adhesives undergoing block shear tests required in the proposed standard.
Specimens in this study were evaluated under five test conditions: dry, vacuum-pressure wet or re-dried, and three-cycle boil-dry-freeze wet or re-dried. Dry and re-dried test conditions are the proposed test protocols for the draft CSA O112.10 standard.
In terms of shear strength and percentage of wood failure, EPI and MUF40 met the requirements of CSA O112.9 for the dry test condition, and PUR did not.
The following block shear test requirements are recommended for CSA O112.10, based on the 95% lower confidence limit of the EPI test results, and structured to be analogous to the requirements of CSA O112.9:
Median dry shear strength = 10 MPa (1450 psi) (adopted from CSA O112.9);
Vacuum-pressure re-dried median shear strength = 7.4 MPa (1070 psi);
Median percentage wood failure = 85% for all the proposed tests (adopted from CSA O112.9); and
Lower quartile percentage wood failure = 75% for all the proposed tests (adopted from CSA O112.9).
The above requirements will be discussed in the CSA Task Group, which will eventually make recommendations to the CSA Standards Committee.