Deep Dive:
Formaldehyde-Free Plywood
Plywood vs. Natural Wood for Construction
Initially, I wanted to make the entire exhibit structure out of wood sourced from the UConn Forest. However, I decided to use slotting design so that the exhibit structure itself wouldn’t require any hardware. The fact that my entire exhibit slots together means that it has very specific dimensions and tolerances. Otherwise, the slots won’t line up and the whole thing won’t assemble.
First, the vertical supports slot into the horizontal curved pieces (dubbed hot dogs) with alternating slots.
Then, the vertical supports are placed into top and bottom hot dogs with centered slots. In the final exhibit structure, the upper hot dogs are replaced with pieces that form rings connecting the three walls.
Given the high degree of precision necessary for the exhibit, I decided to use plywood, which is more dimensionally stable than natural wood because of the way it is made. In natural wood, the grain follows the entire length of lumber in one direction. Depending on the grain direction, natural wood will have the tendency to warp. Plywood, on the other hand, consists of multiple inner layers of wood that criss cross in opposing grain directions with a layer of veneer on each outer side. All the layers are glued together. These criss-crossing layers of grain help to prevent movement in the material.
A diagram illustrating the alternating grain in each layer of plywood.
I noticed just how much tolerances matter when I installed the exhibit in its second location, the Gant Science Complex Light Court. Wood materials absorb or lose water as environmental humidity changes, altering its thickness throughout the seasons. Material World was initially built in the winter, when humidity was lower. When I installed it in the summer, all of the joints were much tighter because the higher humidity led to the wood swelling.
It took more time, more force, and more frustration to get all the joints to go together.
While assembling the exhibit in its new location during the summer, I used clamps to try to pull the walls together once they were upright.
After a day of wrestling with the structure, I could not get all the joints flush, and so the top ring holding all the walls together would not slot on. I returned the next day with a harder mallet and a team to help me.
In most plywoods, the glue used to hold each layer together contains formaldehyde, a known carcinogen that causes irritation to the eyes, nose, throat, and airways. The health impacts of formaldehyde span the supply chain, from the people who manufacture the formaldehyde, glue, and plywood all the way to the occupants of the spaces in which the plywood is used. The impact goes beyond the environment and enters the realm of justice, as the fenceline communities near plants that manufacture such unhealthy chemicals and products are more likely to be low-income or people of color.
I needed to use a mostly dimensionally stable material like plywood, but also wanted to avoid the harms of binders containing formaldehyde. I decided to use PureBond Plywood, which is a formaldehyde-free plywood that uses a soy-based binder. This plywood is comparable in price and quality to traditional plywoods that contain formaldehyde. It is also widely available for consumer purchase.
Plywood Exhibit Structure: Process
To develop the exhibit structure, I first designed rough conceptual ideas in Rhino. After settling on a form, I eventually arrived at the aforementioned slotting concept.
To test the concept, I cut a mini wall prototype on the CNC machine. This also served as an opportunity to test tolerances. After the pieces came off the CNC machine, I had to do some refining, primarily in cutting out the round corners left by the CNC drill bit. Once assembled, the model proved that the slotting method should work.
The mini wall prototype on the CNC bed mid-operation.
After squaring the corners of the slots, I was able to assemble the mini wall.
With the prototype completed, I went ahead and finalized drawings for the CNC machine. Working out the measurements for this part was incredibly important, as if any slot was off by even a sixteenth of an inch, the exhibit might not assemble properly.
Certain CNC layouts in Rhino have remnants of measurements and guides used to make sure that the different slots are correctly sized and placed.
Before cutting the exhibit, my connection at COR²E Mechanical/Glass, Mark Drobney, who machined the structure for me based off of my cut files, ran a tolerance test that proved to be far too loose. When assembled, the pieces wiggled, whereas I needed something closer to a press fit.
Two tolerance tests, representing the two types of joints in my exhibit structure. If you look closely, you can see gaps between the pieces at the joints.
To fix this issue, we ran a second tolerance test that worked much better. I then readjusted all my drawings to match those dimensions, and also added a relief for the CNC machine cutter bit that would eliminate the need to manually square each corner. Once completed, I sent a cut list along with the final .dxf cut files off to be machined.
Each slot in the exhibit has a relief for the cutter bit. The reliefs are hidden when the exhibit is assembled.
There were seven different cut files for the exhibit, requiring 12 total sheets of plywood. Plywood remnants were used to make filler panels in the exhibit.
Once I received the pieces, I had to go through the finishing process, which involved sanding with a fine grit, cleaning the sawdust off, and then applying a first coat of PolyWhey. After the first coat of PolyWhey dried, I went through and sanded the pieces again with an even higher grit sandpaper, cleaned them off once again, and applied a second coat. In total, I had forty-two exhibit structural pieces that I had to sand and coat twice on every side. This labor took up much of my time (and space) leading up to the first install of the exhibit.
Structural pieces of the exhibit stacked together after being sanded for the first time.
33 of the 42 plywood structural members laid out and drying after having one side coated with PolyWhey.
Evaluating Sustainability
The benefits of this plywood primarily lie in human health. The absence of added formaldehyde benefits both consumers and those working along the supply chain. While PureBond Plywood can be specified to be FSC certified, a certification that indicates wood came from sustainably-harvested forests, I don’t believe the plywood that is most often commercially sold is FSC certified. This indicates, although does not necessarily guarantee, that the plywood creation could harm environmental health.
A potential opportunity to avoid the energy and material resources necessary to create virgin plywood would be to reuse plywood or another material. While it could be hard to source this material, once found it could function well as a structural component. For instance, I considered sourcing plywood from a theatre on campus. A trade-off here, though, is that the origin of the plywood would likely be unknown, and so the reused plywood might contain formaldehyde, thus harming human health. How are these potential tradeoffs weighed in decision making?
Additionally, while natural woods, if placed back in the forest, would compost back into the earth, the presence of glue in the plywood, as well as the finish I used on it, PolyWhey, means that it cannot biodegrade without leaving plastics behind. I plan to negate this issue by reusing the plywood structure after the display life of the exhibit is over.