Drywall is Interesting

In just a few weeks I’ll be contributing to a How-to-Drywall workshop for the Asheville Tool Library. This workshop is part of a new series of classes, offered at no cost, where members and the public alike are invited to participate in hands-on learning in a wide range of useful home-repair adjacent skills. These classes are offered in the spirit of the Asheville Tool Library’s mission to provide access to both low-cost tools and knowledge to the people of Western North Carolina. Next year, we’ll be offering classes in basic carpentry, welding, plumbing, tool sharpening, and even automotive repair. For each of these classes we’ll try to go beyond the basics, seeking a contextual understanding of why these seemingly innocuous technologies are so important, ubiquitous and interesting.

Drywall is interesting

If you live in the United States, you already know what drywall is. You’re surrounded by it. Aside from a few windows and doors, the interior walls and ceiling of your home is likely almost entirely encased by it. And for good reason: drywall is more than a benign surface to hang pictures on. It is fire resistant; it makes walls more rigid, and has great sound-insulating qualities. Drywall is very easy to install and repair. Most of all, drywall is cheap. 

In fact, drywall production has become so cheap that it could be considered among those technologies contributing to a “democratic leveling” effect. These are the technologies that are so common they hardly go noticed - plastics, refrigeration, electric motors - that have become so cheap they contribute to raising the standard of living for all on a massive scale. The inconvenient truth however, is that raising the standard of living for all comes at a great cost to the environment. 

Drywall is predominately made from gypsum that must be mined, ground and calcined before forming into sheets and transporting - sometimes across oceans - to its temporary resting place on the walls and ceilings of homes and commercial buildings. The carbon footprint required to manufacture drywall alone is an estimated .38 kgCO2e / kg of product. The scale of the drywall production and disposal pipeline in the United States is immense:

Gypsum mine, Wikipedia commons

• According to the Gypsum Association, upwards of 20 BILLION square feet of drywall is produced in the United States every year.
• An estimated 12% of landfill-destined drywall is clean scrap from construction waste.
• 600 million tons of construction and demolition waste were landfilled in the United States in 2018. Up to 90% of this 600 million tons is accounted for as demolition waste.

Aside from fossil fuel requirements to mine raw materials and transport finished products, drywall production is closely tied with other dubious forms of energy production in surprising ways (more on this later). Drywall itself is predominantly made from gypsum, which when blended with organic materials in a wet, anaerobic environment will break down into pungent hydrogen sulfide gas that makes landfills especially foul-smelling in low-concentrations, and is outright toxic in higher concentrations.

So what then are we to do about the problem of drywall waste? We can start by wasting less to begin with. Some stores offer alternatives to the standard 4’x8’ sheets that are more appropriately sized for smaller jobs. And we do have clean drops, they can be listed in community-sharing networks such as freecycle.org. At risk of sounding too preachy: we can also appreciate what we already have. Our buildings are subjected to forces of fashion that our cars, appliances and clothing are – a form of planned obsolescence of its own - and though modern building codes demand that we build structures that last, changing tastes often have us remodeling more than necessary.

There have been initiatives to reclaim drywall as fertilizer. Gypsum contains Calcium and sulfur are important plant nutrients and as calcium sulfate both can be applied without significantly affecting soil pH. Unique among other calcium fertilizers, gypsum moves through the soil profile with ease, allowing for faster, deeper applications of calcium into root zones. Still, this requires considerable processing; drywall is not just paper and gypsum, fertilizing carries a risk of soil contamination.

Lastly, when we do create drywall waste, we can recycle it. But to understand how drywall is recyclable, we must first take a closer look at gypsum.

The Story of Gypsum

Calcium sulfate, is a simple compound of calcium and sulfur ions found naturally in sedimentary deposits of dried, ancient sea beds. In its natural, weathered state, calcium sulfate is found in its hydrated, crystallized form. Hydrated calcium sulfate is what makes up the ‘sand’ of the White Sand Dunes National Park. It’s the ore found in one of the many gypsum mines scattered throughout the world.

CaSO4·2H2O(s)

Calcium sulfate dihydrate, or gypsum, is a solid, soft crystal that contains 2 molecules of water per single atom of Calcium and four atoms of Sulfur.

Here’s where things start to get interesting: When calcium sulfate dihydrate (gypsum) is heated, nearly all the water is driven off, and what’s left behind is calcium sulfate hemihydrate (more commonly known as plaster of paris) that is no longer hard, but rather soft and easily powdered.

 CaSO₄ · 1/2 H₂O

 Add water back to calcium sulfate hemihydrate, wait for it to cure, and it reverts back to hydrated, interlocking, crystallized gypsum molecules. Water is the mechanism by which we can work with plaster powder and cast interesting shapes and architectural moldings, or coat our walls for smooth, relatively clean surfaces. It is also the key to the inherent fire resistance of drywall: it takes considerable heat to drive off all the molecular-bound water before gypsum crumbles and exposes the wood behind it.

Gypsum to Drywall

Dehydrating raw gypsum is the first step in manufacturing drywall. Water is blended back in, along with other additives, which may include fiberglass for strength, lime or clays as filler, plasticizers or biocidal agents, or even waxes and starch. This slurry is then poured onto a continuous roll of paper, where it is leveled, topped with paper, cured, and formed into common sheets.

Recycling drywall is almost as simple as repeating this process. On clean scraps, paper is removed before re-calcining the gypsum board. On more contaminated scraps, paper is likely discarded entirely and more care is taken to reclaim only the gypsum underneath. Currently almost all drywall recycling is limited to clean scraps. If it weren’t for the paper or other organic additives, drywall is nearly perpetually recyclable. Despite this, drywall producers in the United States continue to rely almost exclusively on virgin gypsum.

A Plot Twist

About 20 Million Metric tons of gypsum are mined in the United States every year. Most domestic-mined gypsum is used in the production of drywall, some used in niche industrial applications, and the remainder used as a fertilizer or concrete additive. Here’s where things get really interesting: not all of our domestic gypsum is mined; in fact, up to 40% of our domestic gypsum is artificially produced.

Remember acid rain? Acid rain is produced when sulfur dioxide gas reacts with water in the atmosphere to create sulfuric acid. Lesser known is how the Clean Air Act of 1990 largely defeated the problem of acid rain in the USA by regulating emissions of these problematic sulfur compounds; the story of synthetic gypsum is HOW these sulfur compounds are removed from industrial smokestacks.

Sulfur dioxide is created when high-sulfur fuels such as coal are burned to create steam at coal–fired power plants. Following the Clean Air Act, a process known as Flue Gas Desulfurization was widely implemented to remove sulfur from these emissions streams before being released into the atmosphere. The process employs the widely available and extremely cheap Calcium Carbonate (limestone, eggshells, seashells) in a double-displacement reaction: Essentially the sulfur ions swap places with the carbonate ions, resulting in two new compounds, Calcium Sulfite and Carbon Dioxide.

CaCO3(s) + SO2(g) → CaSO3(s) + CO2(g)

Now take the Calcium Sulfite (only 3 oxygen atoms), add water, and further oxidize it to create our familiar friend, solid, hydrated Calcium Sulfate (4 oxygen atoms).

CaSO3(aq) + 2 H2O(l) + 1/2 O2(g) → CaSO4·2H2O(s)

Synthetic gypsum, or FGD (flue-gas desulfurization) gypsum is identical in composition, and possibly even more pure than many sources of mined gypsum. As a consumer, it’s impossible to tell the difference between the two.

Complexity Abounds

At drywall production facilities, the choice to use FGD gypsum depends largely on proximity to mines or power plants and other industrial sites. Most domestic gypsum mines are in the west and midwest. Many domestic coal-fired power plants are still in operation, many of which are located in the midwest and mid-atlantic and southern states. Still, for the most part, many coal power plants are switching to natural gas, and FGD gypsum is expected to become less of a factor in the future. These areas, where drywall manufacturers are currently sourcing FGD gypsum, are the most likely to incorporate recycled gypsum into their products. Still gypsum remains a globally traded commodity, and unless some kind of action is taken to limit imported gypsum, it’s hard to say whether we’ll see the environmental benefits of large-scale gypsum recycling anytime soon.

On the surface, drywall is as mundane as it gets. Look a little deeper and there’s an example of how we rely on a complex system that ties together economics, chemistry, environmental ethics, and human behavior.

Addendum, Just for fun: DIY Drywall Recycling

Here’s the fun part: drywall recycling is not exceedingly difficult and makes for a unique material for casting and carving. It’s a process you can easily explore for yourself at home if you have a toaster oven and some scraps of clean drywall:

1. Start with some scrap drywall, clean drywall is easiest, but for this process painted drywall works too.
2. Break into smaller pieces and remove the paper. I found this step was much easier if I soaked the drywall bits in water for a while.
3. Air dry the gypsum chunks and lightly crush.
4. Arrange for maximum surface area and arrange on a oven-safe tray
5. Bake around 375 degrees for at least an hour. There is a definite odor as it gets up to temperature…probably the result of organic compounds, and it is definitely advised to vent properly and stay clear during this stage.
6. Stir occasionally to encourage moisture to vent off covered bits
7. Let cool and crush into power. The dehydrated gypsum should crush very easily
8. Now, treat it like plaster of paris, and experiment! I found it easy to work with when adding water until reaching a peanut-butter-like consistency.

One-of-a-kind, Bespoke, hand-made,locally produced drywall!

Poured into an egg-shaped mold, and cured quickly even at close to 2” thick.

Farewell Living Web Farms

One decade after our first test-run of the new biochar production system, it’s time to formally say farewell to Living Web Farms. For almost 15 years Living Web farms functioned as a working demonstration farm, specializing in biological-centered regenerative agriculture, showcasing 'farm-scale' biochar production, along with unique renewable energy and water management systems, and intensive grazing in a serene, pastoral landscape just south of Asheville NC. Thanks to the generosity of Living Web’s funders many of us were able to donate a considerable amount of food and dedicate many of our working hours to exploring new approaches to biological-centered farming.  However, most of my work in particular centered around biochar, first as for-profit production facility manager, and then later in the exploration of biochar production as it fits in a broader, more circular, economy.

No hyperbole here: Biochar production is a core appropriate technology; a carbon-negative waste management tool that sequesters carbon, produces energy and improves soil.

It’s in this spirit of exploring a more circular economy that I’ll continue to write about my future work here in this space. For now, I’d like to share some of my previous work with biochar production in the context as an 'engine' for a circular economy.

Energy Production:

Pyrolysis of woody biomass requires a heat source to get going, but the process becomes a self-sustaining exothermic process after just a short time. Biochar systems can be designed with energy reclamation in mind, from simple cookstoves to syngas-fueled electricity generators. The system at Living Web took a low maintenance middle-of-the-road approach by employing large gas to water heat exchangers to reclaim as much heat from flue gas as possible. Stored as hot water, typically varying seasonally between 90 and 130 degrees F,  we were able to most successfully use reclaimed ‘carbon-negative’ heat for a variety of targeted applications. One of our more effective applications involved circulating heated water through table-mounted mats made from repaired solar pool heaters. These tables were installed in our greenhouse and used to germinate seeds and keep early summer starts warm before transplanting.

Single flat of lettuces on repurposed solar pool heater turned Biochar process heating mat

Waste Management:

Biochar can be produced from many different sources of biomass, including waste wood from sawmills, or agriculture residues that are otherwise burned or left to rot. In this regard, biochar production is considered a viable tool for waste valorization. At Living Web, we took this a step further, diverting excess process heat for recycling (otherwise, non-recyclable) waste plastics. Here, HDPE flakes were placed in a mold, and heated to upwards of 400F for over 4 hours before being removed and pressed in a purpose-built screw press. This process is described in full here. Pictured below are two of my favorite projects, a 30 lb planter and cruiser style skateboard made from IBC totes and 50 gallon drums.

30 lb, 10 gallon planters, molded from HDPE drums using biochar process heat

Detail of skateboard, molded from stained IBC containers, considered too dirty to recycle

Carbon Sequestration:

Biochar in soils is widely considered a useful mechanism for sequestering atmospheric carbon in soils for many lifetimes; we can look to 19th century technology for another way to employ biochar production to temporarily tie up carbon: Asphalt. Much of the current work with biochar and asphalt is centered around char as a replacement for some aggregate in conventional asphalt blends - and for good reason. However, in 2019, the living web farms biochar crew looked to capturing heavy condensates from pyrolyzed lignin (tar) as a binder for conventional asphalt. Replacing all petroleum-based binders with wood-based binders, simulating an early recipe for “tarmac”, we made a few sample chunks of what a bio-based asphalt may look like today.

4 years later: Our sample section of Bio-Asphalt with pyrolysis oil binder still holds its shape

Soil Fertility:

Last of all, and perhaps most importantly, biochar plays an outsized role in enhancing soil fertility. In sandy soils, biochar can hold nutrients and retain much needed water. In our western North Carolina clayey soils, biochar can lower bulk density and allow for gas exchange into the root zone, simultaneously holding on to water when needed and facilitating drainage during heavy rains. Perhaps most important is the role biochar plays in promoting biologically active soils by moderating extremes and providing safe haven for microbes. It’s been nearly a decade now since I first used a small roto-tiller and applied biochar at 6-8” depth around my decaying oak stump. In the past I spoke at length about various ways to ‘inoculate’ biochar, but my experience shows that simply burying biochar deep into the root zone and following with successive mulching of ramial wood chips has yielded the most robust, fertile and biologically-active soils on my property. Contrary to conventional organic gardening wisdom, many of my nitrogen-hungry vegetables, including corn, okra, melons, squashes, eggplants and tomatoes thrive in these beds conditioned only with biochar mulched only with ramial wood chips.

Biochar in the root zone, and ramial wood chips applied as a mulch are a perfect pairing for fungal-dominant fertility

Farewell Living Web Farms

Although farm operations have ceased, Living Web Farms will continue to operate in a limited capacity with an online presence; previous blogs are still posted and our extensive YouTube catalog will continue to be managed. For those wanting to learn more, I’m especially proud of my previously shared work with plastic recycling, urine as a fertilizer, and my deep dive into applications for wood ashes. Our workshop on biochar inoculation has proven very popular, and I’ll have much to add with my work with homegrown paint in this space in the coming months.