Fighting Water Penetration in Stabilized Earth Brick Construction
One of the most difficult parts of an architect’s job is the constant battle to keep water from penetrating a building. If water, in large quantities, is allowed to penetrate a building’s skin it may rot and corrode and warp and stain as well as question the performance of a building. This is why it is such a large factor in the design of buildings as well as wall systems. It is also why buildings must be properly drained, and the materials that compose the building must be recognized for their individual reactions to water.

When a building is built out of something porous such as masonry including brick, concrete, stucco, and other natural stone materials the designer must take into account how water affects these material differently. In stone and masonry construction the designer must realize that what he is working with is soil that either through natural means or a man-made process has become stabilized enough to build with.

In the example of stabilized earth bricks the construction process of individual bricks is fairly apparent. When working with something like stabilized earth bricks the designer must keep in mind a multitude of variables. Although there is uniformity in the construction of the individual bricks it is not as exact as the construction of bricks or concrete masonry units (CMUs) where each unit has a factory standard that the builder is guaranteed to use. In stabilized earth brick construction there is a much larger room for err. Variables such as consistency of the mix, amount of moisture in the soil prior to mixing, as well as others create inconsistencies in stabilized earth brick construction.

Because stabilized earth brick construction is such an inconsistent way to build it is very important for a designer to use building systems that will not bring any more uncertainties into to a building’s construction systems. This is especially true when it comes to the way in which a building fights the penetration of water.
The penetration of water can be fought in two different ways. The first is through the material itself. In stabilized earth brick construction this would include how an individual brick is fabricated. The second way in which water penetration can be managed is through wall construction techniques. Many of these techniques are similar to those used in other masonry constructions. This is because there are so many similarities between all types of masonry construction that it is only the differences that a designer truly has to worry about.

Construction of Individual Bricks
When constructing stabilized earth bricks there are basically three ingredients. They are the soil, the stabilizer, and water. Each of these elements has an impact on the final outcome of the brick. It is the consistency of the soil’s make-up that is probably the most variable of all of the ingredients. But as it turns out there is probably not enough variation to noticeable affect the performance of the brick. On the other hand the amount of water added to the mixture as well as the type and amount of stabilizer added will cause distinctly different outcomes when it comes to the performance of the brick.

Stabilizers
In stabilized earth brick construction it is best to use a soil that consists of about 80% sand. This is due to the fact that unlike clay sand will not shrink when cured. The shrinkage of clay in brick construction will lead to cracking. Unfortunately sand, unlike clay, will not cement itself together. That is why a stabilizer must be added to the mixture. There are many viable options when picking a stabilizer but the three most popular stabilizers are Portland cement, fly ash, and asphalt emulsion. Both of them work well for the purpose of stabilizing earth bricks, but when considering water absorption cement does absorb more water than fly ash, but the amount is negligible enough that water absorption should not be considered a reason to choose fly ash over cement. In neither the case of the fly ash nor the cement does the stabilizer fight water absorption into the earth block, but this is where asphalt emulsion differs. Asphalt emulsion does fight the water absorption of the brick as well as works well as a stabilizer.

Additives
Another way to fight water absorption during the construction of stabilized earth blocks is with the inclusion of chemical additives. There are many companies that make chemicals for typical brick wall constructions that would apply to stabilized earth bricks as well. These chemicals are typically made to be applied to the surface of the bricks and create a barrier to fight water absorption.

Shape
There are also many advantages that are created by the fact that in stabilized earth brick construction the builder makes the bricks. Because the builder makes the bricks a designer can specify a particular shape of brick. This can be used to make joint between bricks less susceptible to water penetration. A designer can take advantage of gravity to create a water barrier. This can be seen in fig. 6. This is an advantage that does not exist in factory made brick construction. A typical brick is specified as rectangular and therefore the joints can be penetrated by water more easily.

Constructions of Stabilized Earth Brick Wall Systems
There are two categories that masonry wall constructions fall under. They are either veneer or loadbearing wall constructions. A masonry wall is considered loadbearing if the masonry units that compose the wall are also the structural support for the wall like in fig. 3. If there is another means of support for the wall, such as stud frame construction, then the wall is considered to have a masonry veneer like in fig. 1, 2. Both loadbearing and veneer masonry walls have distinct characteristics, but many of the systems used for water control are similar, the differences falling mostly into the realm of thermal qualities. In modern construction the majority of exterior walls are considered cavity walls. What this means it the wall consists of two layers with an air cavity in between them. The purpose of this cavity is to drain water that soaks through the exterior, masonry layer.

Drainage of Masonry Walls
Masonry is a porous material there must be a break in between the interior and exterior of the walls. If there were not air cavities water would be able to get through the wall and create moisture on the inside of buildings. The way the system works is the water that is absorbed into the masonry is able to drain into the air cavity then through a series of weep holes the water can be drained to the outside of the wall again. A weep hole is a break in the mortar joint that is created during the construction of the wall. Weep holes are placed approximately every 24 inches along the masonry wall. They are placed at any point that there is a horizontal break in the wall and along the bottom of the wall as seen in fig. 1, 3. This means over windows, doors, etc.

The other component to water proofing a masonry wall is flashing. Flashing is a water barrier that is place at all corners of a building, where water is liable to penetrate. Along the entire bottom of the wall there is a layer of flashing that helps move the water out the weep holes instead of running back further into the wall.

Roofing
Even though masonry walls are built with water absorption in mind a designer should try to keep the amount of water absorbed to a minimum. One technique is to design the roofing system so that the water is drained off of the walls. This is achieved primarily though overhangs and gutters. They are used to drained water away from the walls; this is typical in pretty much all wall construction. It can be seen in fig. 3.

Mortar Joints
The mortar joints of a wall can become extremely vulnerable points in a wall's ability to fight water penetration if proper care is not taken to weatherproof these joints. The way in which a joint is weatherproofed is by shaping the mortar inside the joint. There are many ways to shape a mortar joint but only three are really affective in resisting water. Those are the concave, the vee, and the weathered joint shown in fig. 5. The ways these joints are shaped allow for water to drain out of the joints. This is important for two reasons. First, even though water is allowed to be absorbed into a masonry wall you want to keep it to a minimum, so the less water that is absorbed through the joints the better. The second reason is that if water is allowed to reside in joints and the temperature changes and the water freezes and thaws then the joint will crack.

Joint size is also an important factor in water absorption. This is because a mortar joint’s purpose is to work as a breaking point for the wall. It is preferable for the joints to crack instead of the individual bricks. Therefore when using a material such as stabilized earth bricks because of the inconsistencies from brick to brick there is the possibility of some bricks absorbing more water and growing thicker than other bricks. The way in which a designer would design for this is a thicker mortar joint. With a thick mortar joint there is more room for the inconsistencies in the bricks.

Wall Coverings
Another way to decrease the amount of water that is absorbed into masonry walls is though covers. Covers are designed to protect the masonry wall from the moisture of rain. There are many types of covers used to protect masonry wall. They include stucco, rainscreens, and ordinary paint. Although there are others these are the three most commonly used. Each type of cover has its own advantages and disadvantages depending of the aesthetic that the designer wants to convey. One of the potential downsides of a protective cover is that they block the view of the masonry wall.

A stucco finish is comprised of three layers of a plaster-like material that naturally lets the moisture breathe out of a wall. In this type of construction weep-holes are not required because the moisture naturally drains out of the stucco finish. Stucco does totally cover the masonry wall. This can be seen in fig. 2.
A rainscreen usually consists of a series of horizontal members. The purpose of these members is to block rain as well as equalize the air pressure between the rainscreen and the masonry wall with that of the interior of the building. This is important to keep water from be sucked into the wall due to the high pressure of wind-driven rain. The horizontal members run the entire face of the walls with only gaps in between them. This can be seen in fig. 4.