Rammed Earth Construction

Rammed earth, an ancient building technique, may have originally been developed in climates where humidity and rainfall did not permit the production of soil block. For soil block to cure uncovered, there must be at least 10 rain-free days. Soil mixtures for rammed earth are similar to those for soil block. Soils with high clay content may be more suitable for ramming, as they tend to crack in blocks when curing.

Preparation and Transport of Soil

1. Rammed earth soil mixes must be carefully prepared by screening, pulverizing, and mixing. Pulverizing is important to ensure a uniform mix and to break up any clumps.
2. Transporting the soil mix to the forms is a demanding tasks. Large quantities of soil must be moved and transported vertically for placement in the forms. This process is not the same as pouring concrete, because the material is not liquid. Traditionally, workers passed baskets or buckets of earth up to where it was needed. Hoists can also be used effectively for this task.

The Ramming Process

1. Once a soil "lift" of 6 to 8 inches in thickness is in place, the soil is rammed. Ramming can be accomplished manually or mechanically. Manual ramming is an ancient technique using a large, specially shaped tool with a long handle called a rammer. Rammers weigh around 18 pounds, and have heads of wood or metal. Differently shaped heads are designed to perform ramming for various form shapes, especially for corners.
2. Mechanical impact ramming uses pneumatic ramming machines. Only rammers specifically designed for soil are effective (rammers which are too powerful or too heavy will not work). Such equipment is quite expensive, but impact ramming is highly effective, and if the soil mixture is good, creates high quality rammed earth. Rammed earth will begin to cure immediately, and can take from several months to several years, depending on weather and humidity to complete the process.

Design Methods

1. Rammed earth walls have low tensile strength, and should be reinforced by providing a bond or collar beam. Beams can be constructed of concrete, wood or steel. Vertical reinforcing may also be done, and may be required by some building officials.
2. All openings in rammed earth walls, such as windows and doors, must have lintels to span the opening width. Water flow and moisture control is critical to protect structural walls. Special detailing to accommodate manufactured windows may be necessary to accommodate wall thickness. All openings for doors and windows will require a frame. Wood, as opposed to metal, is recommended due to the corrosive action of moisture from the soil material. Lintels can be concrete, stone or wood. Careful attention to both roof and opening details is necessary to protect the structure from water damage.
3. Foundations required by most codes are concrete reinforced with steel. Soil block material may be used as a filler material between piers of a reinforced concrete pier and beam foundation. Historically, many structures built with earth materials had no foundation, or used sand and gravel foundations. The latter are excavated trenches filled with two parts sand to three parts gravel. Trench bottoms should be graded to provide positive drainage. Soil material block should not be used in below grade walls unless supported on both sides. Natural moisture from the ground may infiltrate the block, resulting in reduced compressive strength.