Low Ply: Wednesday's Word(s) Of The Week

Surfacing glulam

A Low Ply is a spot on the side of a glulam member that does not get surfaced when the rest of the member is planed to size. For example, when we are making a 5" wide finished beam, we will start with 2x6 material which is 5½" wide. After the material is finger joined and glued to the full size beam blank it will go through our large planer and ideally remove ¼" from each side to end up with a 5" wide beam perfectly planed.

Of course, nothing is perfect when working with wood, so sometimes a ply will be more than ¼" out of alignment with the rest of the beam, in which case that spot will not be planed. That spot is below the planed surface of the rest of the beam, hence a "Low Ply."  The two main causes of this are lumber with crook (curve in the wide direction) and alignment of finger joint teeth. Often the two of these go hand in hand and result in a short section of Low Ply. 

Some unfinished Low Plies are allowed in Industrial Grade glulam members. For Architectural Grade, the area is routed out and visually repaired with a plug.

*Wednesday's Word Of The Week is a feature on Unalam's Wood Times Blog. Each Wednesday our structural engineer, Rik Vandermeulen, will discuss a new term associated with glulam manufacturing. He will do this until we run out of words. If there is a timber or glulam term that you have heard of and want to know more about, let us know in the comments.