Originally Published: June 1, 2015 5 p.m.
When it comes to alternative construction methods, little else is as authentic and time tested as adobe. Adobe structures can be found across the globe, and comprise some of the oldest remaining structures on the planet. Similarly here in the US, adobe construction is one of the oldest building techniques that is still in use today for contemporary structures.
Essentially used as a block material, adobe was originally composed of nothing more than moistened dirt, formed into crude bricks, and then set out to dry in the open air. Early improvements included the addition of straw or other fibrous components for added strength. Once dried, the roughly uniform blocks can then be stacked like bricks to form walls. With a proper sub-floor, the right sealant and routine maintenance, adobe can be used for earthen flooring as well.
Adobe's longevity can be attributed to the fact that it is both load bearing and insulating. Local building codes will dictate the minimum compressive strength required of the individual adobe bricks, which are typically quite adequate structurally - except in areas with high lateral stresses, or that are at risk for strong earthquakes.
While the presence of clay is considered problematic when it comes to foundations, the most durable adobe is composed of at least 15 to 30 percent clay, which is needed to bind the more granular components of the base mix together. More clay than that can lead to shrinking, swelling, and the eventual cracking of the adobe over time. Less than that and it becomes difficult to form solid bricks for drying. Adobe blocks can be either formed by hand using open wood trays or "ladders", or can be mechanically compressed into uniform bricks using a hydraulic press.
Contemporary adobe construction often calls for cement or other emulsifying agents to be added to the adobe base mix in order to protect against deterioration. Known as "stabilized adobe", many building codes now require this in order to approve plans for permit and construction. Although not recognized by most building departments, an organic alternate for stabilized adobe is also available by adding processed animal manure and ash to the sand and clay mix, instead of cement.
PRESSED VERSUS "PUDDLED" ADOBE
In addition to determining whether or not your next building project will require stabilized adobe, another option to take into consideration is whether or not to use machine pressed bricks versus the handmade variety- which are also referred to as "puddled" adobe.
For larger projects constructed on tighter timeframes, machine pressed adobe provides several advantages. Pressed adobe is appreciably stronger than hand-made, and is faster and more efficient to construct due to its greater uniformity in shape and size. Machine pressed adobe is also considerably more dense than puddled adobe, providing a more efficient thermal mass. Because of the reduced labor, pressed adobe bricks can also be produced much more quickly, and in far greater numbers than with puddled adobe.
Additionally, pressed adobe requires little to no drying time, as nearly all residual moisture is mechanically squeezed from the blocks by the hydraulic force of the press. Pressed adobe bricks can be ready for construction the same day. By comparison, puddled adobe bricks will need anywhere from one to four weeks to dry, depending on the weather. Because of its reduced moisture content, pressed adobe can also be made year round- whereas handmade/puddled adobe prefers moderate temperatures and low-humidity conditions for effective drying and construction.
Handmade individual bricks formed with puddled adobe can be a better choice where the pressures of schedule, available labor, and thermodynamic performance are not overbearing. The primary advantage of puddled adobe is that it has a less uniform and more organic character, yielding a slightly more rugged, authentic looking, and visually appealing aesthetic.
Because of adobe's ability to diffuse heat more slowly than comparable materials such as concrete, stone, and most concrete block, it is an ideal choice for our southwestern climate of warm days and relatively cool nights. The high thermal mass of adobe allows for an exceptionally efficient "thermal flywheel", which helps keep the structure cool inside during the day (spring, summer, and fall months) as the building passively stores heat within its exterior walls, then releasing that stored warmth to the interior during the cooler nighttime hours.
An adobe building can significantly reduce or even eliminate the need for supplemental heating or cooling of the structure. An off-grid home powered only by photovoltaic panels is easily achievable with adobe construction.
Design-wise, several factors are critical for successful adobe construction. Among these are proper building orientation with the long axis of the structure running east/west; broad roof overhangs all the way around to help protect the adobe from rain and water damage; a water-resistant base course to keep ground moisture from wicking up into the walls; modest ceiling heights of 10 feet or less; and of course the proper window size, placement, and glazing type for its specific orientation.
For passive solar integration, the relationship between the thickness of the adobe, the amount and type of glazing in the structure (as a percentage of floor area), and other details such as the insulative quality of the roof, floor, and windows, will all contribute to the overall comfort and energy performance of your building.
While adobe walls can be left unfinished, lime-plaster top coats are a natural and beautiful way to complete your adobe home or business. Many other exterior and interior finishes are possible as well, although any product or material that traps moisture within the adobe walls should be strictly avoided.
Adobe is a time tested, readily available, energy saving, and inexpensive construction method. When properly designed and detailed, adobe construction can be an excellent choice for your live, work, or play space. Be sure to consult with your architect or an adobe construction specialist to see if adobe is the best option for your next project.