Effects of Seven Variables on Properties of Southern Pine Plywood: Part IV Minimizing Face Checking

This paper on face checking is the last in a series of four on the properties of southern pine plywood. Three-ply, 3/8-inch-thick exterior plywood was hot-pressed from veneer cut from eight loblolly pine trees selected to exhibit a range of specific gravity and growth rate. Panels were quantitatively evaluated for severity of face checking after several cycles of wetting and drying. Face checking was minimized by 1) Reducing the hygroscopicity of the plywood by dipping the panels for 10 seconds in a water repellent. Checking index was 4.4 for treated panels and 12.8 for untreated. 2) Peeling veneer hot and tight rather than cold and loose. Checking index was 5.5 for tight-peeled face veneers and 11.7 for loose-peeled. 3) Using veneer of low specific gravity rather than high. Checking index was 6.9 for low-density faces and 10.4 for high-density faces. With all the above factors favorable, the average checking index was minimum at 2.4; if all were unfavorable, the checking index was 20.4. Factors that did not significantly affect severity of face checking were: rate of growth (rings per inch in the veneer); moisture content of the veneer before gluespreading; and proximity of the plywood face to the hot platen when pressing two panels per opening.

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