Plywood Types for Climbing Volume Construction

March 1, 2023

Given the shortage of Baltic birch plywood, it’s time to take a look at eucalyptus plywood for making climbing volumes.  Eucalyptus has not been used much in North America until recently, but its popularity is growing due to its sustainability and durability.  Eucalyptus is a hardwood primarily from Australia, Africa, and parts of south-east Asia.  It’s much faster growing than birch, and doesn’t require a lot of maintenance or resources.  These features make it more sustainable and eco-friendly than other slower growing hardwoods.  Eucalyptus is also quite hard, with a rating of 1,125 pounds on the Janka hardness scale, compared to birch with a hardness of 1,470.  Because eucalyptus produces more oils than birch, it is more water resistant, making it a better choice for outdoor use or in places with high humidity.  Eucalyptus plywood can visually appear to be coarse, but it’s actually quite smooth to the touch.  It is sensitive to sanding though and care must be taken not to sand too deeply if the surface is going to be stained or clear finished.  With paint or epoxy such as is used on textured plywood climbing volumes, this feature is no issue, as the paint covers it nicely.  Eucalyptus plywood tends to be slightly less resilient to flexing than birch, and more prone to cracking.  So for large volumes which have plywood panels with a large surface area, it may be worth using braces on the inside to stiffen the panels. 

Plywood is made of laminated layers or thin sheets of wood glued together. Typically the more layers, the more rigid and stable the plywood is. Some plywood are all the same specie of wood in the layers (homogeneous), and some are a mixture of different species of wood laminated together (heterogeneous).  The different color bands, shown in the image below give some indication of how many species of wood are used in making the plywood sheet.  When making climbing volumes, it’s important to choose a plywood with the mechanical  properties that are suitable for the level of use it will see.  Plywood climbing volumes are typically made from a 13 layer cabinet grade plywood that is 18 millimeters (0.709") thick, but in the United States is frequently called ¾” plywood, although technically it’s a little thinner than ¾” (0.750") .  The layers are an important distinction.  You will notice in the image below the Baltic birch and Eucalyptus have a true 13 layers, while the other types have less layers, and the AC grade fir has layers that are noticeably more loose and less dense than the high grade plywoods.  AC Fir will be less durable, less stable, and will not hold a screw without stripping out as well as the 13 layer cabinet grade plywoods. If you plan to use a lower grade plywood it may be advisable to test it on a volume first before using too much, to be sure it will be rigid, stable, and that the glue joints and screws will hold well enough.  

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