Deep Dive: Finishes
Milk Paint
The paint used in Material World is a milk paint manufactured by Real Milk Paint. Milk paints are biodegradable and compostable. They use milk protein called casein as a base, and then are mixed with minerals like clay, lime, and chalk, as well as pigments, to make the color. Milk paint is sold in a powder form. To get liquid paint, the powder only needs to be mixed in a 1:1 ratio with water. It contains no volatile organic compounds (VOCs), which are present in most commercially-available paints. VOCs are chemicals, often human-made, which are emitted as gases. They can have both short and long-term negative health impacts and are present in a wide variety of products beyond paints, including cleaning supplies, building materials, glues, and permanent markers, among many others. Because milk paint doesn’t release fumes, areas in which it is being used don’t need to be ventilated during application and drying periods.
I used a rust-colored paint in my exhibit.
Rust-colored milk paint on the text panel on formaldehyde-free plywood, seen here as installed in the exhibit.
To test different methods of applying milk paint to CNC machined text, I ran a test panel with different finishes.
I decided that the sample painted red with milk paint, then sealed with hemp oil, and finally machined with text, was the most legible.
Seen at the bottom of this image, I tried text tests with two different colors of milk paint sealed with hemp oil.
In the test second from the bottom , I applied hemp oil after machining the text, which noticeably decreased the contrast between the background and text.
Hemp Oil
I used hemp oil to seal the panels painted with milk paint before CNC machining the text into them. The hemp oil is made entirely of cannabis sativa oil containing no THC. When hemp oil was applied on top of the red-orange milk paint, it darkened the color. While making samples of different finishes, I tested applying the oil before CNC machining and after CNC machining. I found that applying oil after CNC machining darkened the text too much, making it hard to read. There was a much better contrast when the hemp oil was applied before CNC machining, as the lighter layers beneath the painted surface of the plywood were unaffected by the darkening effect of the oil. The finished surfaces remained oily for a few days, but later cured hard and could be touched without leaving a residue. Because the oil is only made of compressed hemp oil, it is readily biodegradable.
Click here for the safety data sheet for my hemp oil.
After finishing a painted plywood sheet with hemp oil, I carved out the text for two of the text panels in my exhibit.
Homemade Wood Stain
While applying the wood stain, the areas with more recently applied stain (right) were noticeably lighter.
After sitting for a few minutes, the entire area darkened.
Once dry, I coated the stained areas in PolyWhey, which darkened it further (seen at the left in this image).
To darken the plywood filler panels in my exhibit and create a contrast against the lighter wood tones of the plywood structure, I created a homemade wood stain out of steel wool and vinegar. I simply left a pad of steel wool in a jar of vinegar for two weeks. After letting the steel wool dissolve, I strained out any remaining steel wool bits.
The steel wool and vinegar stain creates an oxidizing reaction that naturally darkens wood. On a test piece, I loved the color created from the stain, and so decided to use it for every filler panel.
There is a great article online about steel wool and vinegar stain that was my main resource for this process.
PolyWhey
I used PolyWhey semi-gloss floor finish on the main exhibit structure, dark brown filler panels, and natural wood elements of the exhibit. PolyWhey is a water-based, solvent-free finish. It is an alternative to water-based polyurethane finishes or the more hazardous oil-based polyurethane finishes, which contain solvents that harm human health in wide-ranging ways, such as through “damage [to] the liver, kidneys, heart, blood vessels, bone marrow and the nervous system.”
The commonality between all of the aforementioned finishes is that they dry to a hard, plastic coat where they are applied, and are often applied in high-use areas because of their durability. Although oil-based polyurethanes are typically stronger than water-based ones, PolyWhey claims that their finish is twice as strong as traditional water-based polyurethane finishes. Although I aimed to avoid the use of plastics in my exhibit, I ended up deciding to use a strong finish like PolyWhey because I anticipated my exhibit to be high-traffic and high-touch, as I invite people to touch the exhibit in my interpretive text.
PolyWhey uses whey to bind the resin together, thus minimizing VOCs emitted by the product. The VOC output of PolyWhey is low enough to qualify for both LEED projects and Living Building Challenge petal satisfaction.
Speaking from personal experience, when applying a traditional water-based polyurethane finish, it had a strong smell and I had to leave the area multiple times because I became dizzy. With PolyWhey, on the other hand, the smell was minimal, and I never became dizzy or lightheaded while using it (and I was working with it for a much longer period of time than the other water-based polyurethane finish).
The full safety data sheet for PolyWhey semi-gloss floor finish can be found here.
I coated all the structural exhibit pieces in two coats of PolyWhey.
The main exhibit structure, dark wood panels (lower left), and natural wood boards (lower left and right) are finished with PolyWhey.
Soft Finishing Wax
I used a soft wax finish, made by Real Milk Paint, to seal my mycelium panels. The soft wax finish consists primarily of beeswax with carnauba wax. The wax is not considered to be carcinogenic or toxic to reproductive health. However, it can cause temporary irritation with prolonged skin contact or eye contact. The safety data sheet for the soft wax can be found here.
The soft wax is almost unnoticeable on the finished mycelium panels.