Traditional wisdom says metal and mud don’t mix because, unlike metal, mud shrinks when it dries causing it to crack, which allows water to penetrate, causing the building to self-destruct. However, sometimes traditional wisdom turns out to be more of an old wives’ tale as the mud hut we built in northern California aptly demonstrates. As a general rule, mud is indeed more compatible with porous organic materials, but general rules can sometimes be broken if there’s a good rationale for doing so and if one knows how…. One of the best reasons to break a “rule” is for the sake of art. So I’m going to invoke my artistic license if challenged on this. However, in this case, there are plenty of other good reasons too.
The idea of reinforcing concrete with metal originated in the 1840s in France. People found that by adding more metal they could improve its tensile strength which made them more earthquake resistant and allowed them to build thinner walls that are even stronger. Thus it’s become standard practice to use it to reinforce concrete ever since. The same advantages the metal offers the concrete can likewise be offered to the earthen walls. The reason I can get away with combining the mud with the metal (despite their seeming incompatibility), is because the high straw content prevents any significant cracking. It also increases the insulation value and reduces condensation.
I’m not asserting that using metal is at all necessary to build a curvy mud house, but by incorporating a relatively inexpensive recycled contemporary material like thin-gauged rebar (a stronger, more pliable, fire and insect-proof substitute for reeds/saplings/vines that doesn’t require any prep work), I can easily create free-form livable sculptures that can actually appear to defy gravity. They would have virtually all the benefits of using earth rather than concrete, and would not be possible with standard masonry methods. This technique I’ve devised (“Wired & Daubed Capless Ferro-Cob”) is a cross between traditional “wattle and daub” (one of the most ancient construction methods), and ferrocement (one of the most modern methods), and has all the advantages of the former, and eliminates most of the disadvantages, notably its susceptibility to rot and fire.
Using earth instead of concrete makes it much “greener” and cheaper than ferrocement with superior insulation and sculptural qualities. Although the metal makes the structure slightly more expensive and a bit less “green” than traditional earthen buildings, this modern version of wattle and daub facilitates defining the shape, and smearing on the mud. This makes it stronger (even with thinner walls), more durable (fireproof), and quicker to build than conventional wattle and daub, which has always been one of the quickest ways to build with earth. Plus, it’s more theft and earthquake resistant, and easier to get approval for building permits since it could accurately be described as a wooden and metal structure plastered with mud-straw. Most importantly, it can prevent a roofless earthen structure from collapsing if ever too much water were to penetrate the hard lime (artificial limestone) shell due, for instance, to a tree branch crashing on it or a large earthquake-induced crack during rainy season.
Normally, the only place one can safely build an earthen structure without a roof is in a dry desert-like climate where there isn’t very much wood available for a roof anyway. In wetter climates, where wood tends to be more readily available, it has always been common practice to utilize a “boots and cap” strategy–meaning raising the structure off the ground and incorporating an overhanging roof to prevent the walls from eroding due to the rain. In fact, it is virtually unheard of, if not considered impossible (perhaps even insane), to attempt to build an earthen structure without a roof in a rainy/snowy climate.
However, after spending years of research trying to figure out how to do so, I am now proud to announce that it is indeed possible as evidenced by the fact that the roof-less mud hut we built in Northern California, in a zone that typically receives 40 inches of rainfall and a significant amount of snow every year, has withstood the last three winters without any signs of disintegrating. The reason I strived for so long to develop such a technique was to allow myself the artistic freedom to design organic-shaped structures that are not only strong, but don’t require a roof, one of the most expensive components of a house. They are completely fireproof, are more aerodynamic, don’t contribute to deforestation, won’t get eaten by bugs, nor will they easily decompose (despite being biodegradable), with a roof that has all the same benefits as the earthen walls provide, and will work in virtually any climate.
The following photo is what the structure we’re currently building in Costa Rica looked like before we began to add the mud-straw. To see more photos of the construction of the metal armature shown below, click here…
Having completed the rebar and mesh “skeleton”, we were then ready to start adding the mud and straw “skin”.
In the next photo you can see the electrical conduit and boxes that were added to the frame for the outlets that will be installed once the structure is mudded and limed.
For the grass/fiber component of the mud mix, instead of buying straw-bales (as I did when we constructed our mud house in California), I opted to use the tall grass-like sweet sorghum that covers most of the property, as you can see from the next photo. It grows really fast and can reach a height of over 3 meters (about 10 feet). Although it’s great for grazing animals and is a staple food crop for millions of people (particularly in Africa, Asia, and Central America), it’s hard to walk through, may harbor venomous snakes, and can present a fire hazard. For these reasons, it’s a good idea to cut it to create clearances around the homesite. Because it’s so plentiful, renewable, and needs to be cut anyway, I figured that I might as well use it for the mud mix rather than have to spend money to buy straw-bales that cost twice what they did in California. Plus, I thought it would set a better example to utilize the onsite resources as much as possible. The photo below shows Olman and Carlos transporting the sorghum in wheelbarrows to the building site.
The disadvantage of using sorghum for this application was that the stalks were so long and coarse, which meant that we had to cut them and wear gloves to work with it because it becomes sharp when cut. We harvested the stalks with a weed whacker using a brush-cutting blade, and Rosendo, our incredibly buff 70-year old well-digger friend, chopped them into smaller pieces using a machete.
In places where the days are hot and the nights are cold, heavy buildings work to ones advantage, serving as a thermal flywheel to help keep the occupants cool during the day and warm at night. However, in tropical climates where the nights are warm as well, the thermal mass can be a huge disadvantage because the walls hold the heat, making them ridiculously hot in the evenings. For this reason, thick-walled concrete structures (the norm in Costa Rica) are a very poor choice that make one dependent on air conditioning to remain comfortable. On any given day (particularly in the evenings), the walls in our cinderblock apartment measure about 100 degrees fahrenheit (38 degrees celsius) and hold the heat all day and all night long. Without air conditioning, I would not be able to sleep, even with a fan. Like concrete buildings, earthen ones tend to be very heavy, but by maximizing the percentage of straw in the mud mix, I was able to make the walls much more light-weight and insulative, which drastically mitigated the problem of heat-retention at night while protecting us from the intense heat during the day.
To make the straw-heavy mix, we soaked the rock-hard clay chunks overnight in 55-gallon drums filled with water and, the next day, used a special high-torque drill with a long mud-mixing drill bit to create a thick mud slurry–almost like making a large thick chocolate milkshake. Although they are much more expensive, I would have strongly preferred to use a mortar mixer but was not able to find one anywhere. Despite the fact that cement mixers are very common in Costa Rica and have been successfully used for this purpose, they are not the optimum tool for the job. Plus, it would have been much more expensive to buy or rent.
After the clay slurry was prepared, it was poured over a liberal amount of chopped straw/sorghum and mixed using child laborers.
Just kidding! Those were kids from the local Waldorf school that took a field trip to our property to learn the art of earth building. In reality, the mud and straw was applied after being mixed using pitchforks with just enough clay to stick the straw together by my excellent helpers, Carlos, Olman, and Byrum Espinoza.
You can tell from the photos just how straw-rich the mix was….
In the next couple of photos you can see the decorative security bars, along with the flexible electrical conduit and octagonal junction boxes for the light fixtures, being mudded into place.
The recycle bin at the local bar was always stocked with these lovely blue beer bottles so I decided to incorporate them into the structure. To avoid having to cut them or leave openings for insects to enter and nest, I duct taped them together so they would be long enough to protrude from the walls with the intention of instilling a beautiful blue glow into the house without having too much light penetrate, causing the house to overheat.
I decided to make a double spiral of them, wrapping around the upper part of the structure. Here I am mudding them into place.
Besides the blue spiral I was working on, here you can see the gray 4-inch PVC pipe being mudded into place that will later serve as a vent for the compost toilet.
In the lower right corner, you can see one of the two cinderblock compost toilets with an opening to remove what will later become very fertile compost.
Here is a closeup of the aforementioned compost toilet being constructed. You can see the gray PVC vent pipe that tees into both toilets to prevent any odor from escaping into the bathroom.
Besides the toilet vent pipe now extending vertically from the conical roof, here you can see the second compost toilet being constructed next to the first one. The basic idea is that when the cinderblock chamber becomes full after about a year, it will be sealed and the second toilet will be used instead. As another year passes by, the fecal matter (along with the toilet paper) in the first toilet will break down and be converted into rich compost. By the time the second toilet chamber is full, the now-composted contents of the first one will be emptied from the opening on the outside of the house into a wheelbarrow and used for fertilizer. This innovation simultaneously eliminates the need for a septic tank, is not dependent on water and saves tons of it that would otherwise be wasted (especially important during the dry season), creates valuable compost, eliminates plumbing problems, prevents toilet water from overflowing and contaminating the house with raw sewage everytime there is a blockage, and won’t vaporize fecal matter like normal toilets do every time they are flushed.
The next few photos show the double spiral of bottles as well as the metal that was used to build the loft, before it was covered with mud.
With the upper part of the structure almost finished, Olman, Carlos, and I put the final touches on the vaults.
To prevent the sun from overheating the structure while allowing the hot air to rise and escape from the apex of the cone, there will be a conical cupola covering the 4-foot (1.25-meter) wide opening. However, I’m disappointed to report that there was not enough time to build it because the rainy season began a few weeks earlier than usual. Walking around clockwise, the next seven photos show what it looked like up until that point:
Rain is the natural enemy of earthen buildings, particularly those built in wet climates that don’t have an overhanging (or any) roof like mine. Therefore, we had to cover the structure with plastic and wait for the rainy season to pass.
In the meantime, we began working on the inside, concealing the metal armature with a thin layer of mud-straw.
What a pleasure it was to work inside, shielded from the hot sun. As you can see, we covered the loft with mud-straw, hiding most of the metal and giving the mud the illusion of defying gravity. Besides covering the rest of the metal framework, we accentuated it with what resembled spiraling coils of mud-straw, using a much finer type of straw to facilitate this sculptural layer.
To access the loft, there will be 12 stairs spiraling around the central post.
To help ventilate the loft, we left arch-shaped openings for the air to circulate through it from below, as you can see in the following photo:
At some point during the mudding process, some of the teak poles slipped out of the 12-pointed star that helped hold them in place. We didn’t notice it until much later on after it was too late to put them back where they were. Though we could have sawed off a few inches of the posts to put them back into place, I didn’t want to lose any height and was concerned about potential condensation dripping onto the loft so, because the star was no longer necessary to stabilize the posts, I decided to repurpose it by using it as our dining room table. It was the perfect size and just needed some legs and a glass or plexiglass top. The table will be located right where it is in this photo:
Due to the possibility of water damage stemming from the fact that the exterior was never finished, I am a bit hesitant to continue working on it until November, when the danger of rain has passed. So stay tuned and I’ll be sure to keep you posted….