Adobe blocks are stacked in alternating directions in order to obtain a thicker wall.
As mentioned in article 1 of this series, thick walls made of a heavy material such as stone or mud help to heat and cool the interior of the home. Most of the interior walls of this home are made of adobe bricks, which are nothing more than mud that has been poured into a form and then dried in the sun. Another option would have been to have used rammed earth. This is slightly damp earth mixed with a small amount of cement (or other form of stabilizer). It is tamped into wooden or metal wall forms that vary from 18" to 24" in thickness. Once compacted, the forms are removed, and the wall is self standing and structurally strong. Pressed adobe block is made by compressing the raw earth in a mold under extreme pressure. If these materials are not appropriate or not available in your area, thermal mass walls can be constructed of stone, brick, or any other dense and heavy material. Ideally, at least 1/2 to 2/3 of the interior surfaces (floor and walls) should be thermal mass.Another option is to use a straw/clay mix or cob. Straw/clay has sufficient mud mixed with the loose straw to make it stick together. Cob has more mud and is a denser material.
Mud mortar is used to hold the adobe blocks together. This mud is made from the same material as the blocks themselves so has to create a good bond.
The average adobe brick measures 4"x10"x14". Depending on how the adobe is oriented, the wall can be 10" thick (the most common) or 14" thick. This home has 10" and 24"-thick interior walls. The 24"-thick wall is made by alternating the bricks side by side using both the 10" and 14" widths (see picture). Mud mortar, and not cement, is used to hold the adobe bricks together. Walls of this thickness are not essential. If your budget limits the width of your thermal mass walls, strive for about 4“ of solid wall thickness as this will give you good performance for your money.
This wall is made from a mixture of loose straw and clay. It is tamped between wooden forms. The forms can be removed immediately and the wall will hold its shape.
The beauty of earthen walls is that they are in a finished state at every phase of their construction. No additional finish is needed as the color and visible construction process are beautiful. The imperfections add character and beauty. In this home, the walls will be earth plastered in order to obtained a smoother texture.
A wood-frame wall must go through several steps of assembly in order for it to be presentable. First, the wood studs are nailed together. This is followed by wallboard that is screwed to the studs. The joints are taped and plastered and the screw holes are filled with spackle. Finally, the entire surface is painted so as to hide the construction process. Any imperfections in the construction will stand out and look like mistakes.
Come back next week as I continue to discuss wall and floor materials.
Update: Part 7 is here.
[This has been a guest post by Ted Owens, a green designer and filmmaker. More details on green building design and construction can be found on his website and in the Building with Awareness DVD and Guidebook. -Ed.]