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There are many ways to build with adobe. The purpose of this information is to acquaint you with the process of building an adobe house as done by Habitat for Humanity in Taos, NM. Since many of our groups come to work for just a week or so, we thought it might be nice to give a brief overview of the process. Our volunteers arrive with a wide range of skills from novice to expert. While a few of the tools used will be mentioned, we will not attempt to teach you how to use them here. On-site instruction is provided as needed.
While we have listed the building steps in approximate order, there are a number of factors that can affect this, including; the timing of receipt of supplies, the scheduling of outside contractors (a majority of the work is done by volunteers but the electric and plumbing are done by licensed contractors), the timing of the various inspections, the availability of volunteers, finances and the weather. And some steps can be carried out concurrently.
Building an Adobe HouseAdobe is one of the oldest building materials known to humans, and has been used for thousands of years in places ranging from the American Southwest to Africa, the Middle East, West Asia, Spain, and South America. In dry climates, adobe structures are extremely durable, and account for some of the oldest existing buildings in the world. Adobe buildings offer significant advantages due to their greater thermal mass and can be perfect for a desert climate as they hold in the proper amounts of hot or cold air depending upon the season. Adobe is traditionally a mix of earth/clay, water, sand, and an organic material such as straw. It can be poured into frames or shaped into bricks, though HFHT generally uses bricks. The term "adobe" has come to include a style of architecture popular in the desert climates of North America, especially in New Mexico.
Most of the Taos Habitat houses are of similar design. They are built on a small, generally flat piece of land. All our recent homes are supplied with town water and sewer, and all are hooked up to electric and gas service. The houses are one story, built of adobe block, which keeps them cool in the summer and warm in the winter and provides volunteers with a unique building experience. The heat is radiant heat; hot water which circulates through plastic tubing embedded in the concrete floor.
Day-to-day construction is done under the supervision of an our licensed construction supervisor.
Before any work can begin an application for a building permit must be filed and approved by the town. This requires the development of a site plan which indicates the property lines and the situation of the house as well as a detailed description of the house showing all its features; doors, windows, internal walls and materials to be used, etc.
A few words about tools and safety. The inexperienced may be exposed to tools with which they are unfamiliar. While you will be shown how to use the various tools, if you are uncomfortable about using a specific tool don't use it until you are ready. Feel free to ask questions. Be careful using tools. Gloves, eye protection and dust masks are available. Even experienced people may not be used to working with a large crew or with less experienced people. Extra care and patience is in order. Be careful of where you place tools when they are not in use. And be extra careful when working with a large group. You may be working on ladders or scaffolding. Unless extreme care is used these can present a real risk of injury.
Adobe bricks weigh about thirty to thirty-five pounds, so you may be working with heavy materials. No one wants you to lift more than is comfortable. There is no prize for heavy lifting and doing so not only puts you at risk but others as well.
When working with "mud" it is important to keep your tools clean both during and at the end of the day.
Protective eye wear is a good idea and it also protects you from dust when it's windy.
Being mindful of the safety of yourself and others will help assure that the building of an adobe house is a positive and enjoyable experience.
Site PreparationFirst the site is cleared and batter boards are erected. Their purpose is to produce an outline of the "footprint" of the house for digging the footing trenches and to serve as a guide in laying cinder block from the footings to above grade. The batter boards are three foot lengths of board staked perpendicular to each other at about three feet from each corner of the house. The actual out line of the house is made by running string from nails in the batter boards. The corners of the house are located where the strings running north and south intersect with those running east and west. It is important to assure that the corners are square. Once the square is assured metal spikes are driven into the ground directly below where the strings intersect at each corner and a line is spray painted on the ground to serve as a guide for digging the footing trench.
Preparing for the Footing PourOnce the footing trench is dug, three rows of rebar are laid about six inches apart in the footing trench. Spacer bars are inserted every few feet and the rebar is elevated using "chairs" designed for that purpose. Any cutting or bending of the rebar is done with a special tool. Where pieces of rebar overlap there should be about an 18" overlap. Next a length of rebar is driven into the ground every several feet. A transit is used to assure that the tops of all are at exactly the same level. These are used as a guide to assure that the concrete is poured to the same level throughout the footing.
The TransitComplete instructions will be given if you are to use a transit. Suffice it to say here that the transit, once it is leveled, set firmly in the ground and assuming it is not disturbed can assure, with a high degree of accuracy, that the target level for the footing pour is consistent.
The Footing PourDuring the footing pour (the concrete is delivered by professionals) the concrete is spread evenly throughout the footing to the height of the rebar stakes described above. Every several feet and especially at the corners pieces of rebar are pushed into the concrete footing before it sets. These are used to tie the concrete blocks to the footing.
Laying the Concrete BlockNext the concrete block is laid. The mortar is made by mixing sand, Portland cement, lime and water until it is loose but not soupy. First, the corner blocks are laid and lines are strung from corner to corner to assure the blocks in between are laid in a straight line and level. Blocks are laid to overlap the blocks below. Overlapping rather than stacking provides strength. This is true with cement block, adobe block, wallboard etc. Each block is leveled both left to right and front to back. As the block is laid the doorways are noted according to the house plan. Once the block has been laid to the appropriate level it is filled with mortar. Two inch foam insulation is then installed on the outside of the concrete block.
Preparing to Pour the Concrete FloorIt is ideal to pour the concrete floor before the adobe walls are erected as this gives much better access to the entire floor area. However, before the floor can be poured there are a number of steps which must be completed. All under-floor plumbing, including the radiant heat tubing must be laid. The ground must be leveled and compacted and wire mesh must be laid. Trenching is done where needed to provide additional support for any internal support walls.
The leveling of the floor is a tedious, time consuming, and extremely important task. First, the earth is leveled and compacted and then fill is brought in and this too is compacted. Then stakes with brackets are driven in periodically and, once again, using the transit, the brackets are all brought to the same height. Pipes are then laid across the brackets and the entire earthen floor is leveled to within four inches of the bottom of the pipe.
Once this process is complete insulation, four feet wide, is laid around the perimeter of the floor and a heavy wire mesh, which adds strength to the floor, is laid covering the entire floor.
The PourThe concrete for the floor is brought in by professionals. The concrete is poured and spread evenly throughout using the metal pipes as guides for depth. It must be assured that the metal mesh neither lies at the bottom nor rises to the surface of the concrete.
The floor is then "floated" to assure maximum smoothness.
Laying the Adobe BlockBefore laying the adobe block, 2x4x8 story boards are erected at each corner and they are marked at 4 1/2" intervals. At each mark a screw is driven and a string is attached corner to corner to act as a guide in laying the adobe block. The adobe block is laid using screened, natural soil with a high clay content, common in New Mexico. As the block is laid and using the house plan, provision for external doors and windows is made. Since the frames for windows and doors cannot be securely attached to adobe block, 2x4" frames measuring 10x14", the same size as adobe block, are constructed. These are placed at appropriate spots and filled with mud. They provide a means of effectively anchoring the door and window frames. They are also placed at appropriate places to secure the framing for internal walls.
External Window and Door FramesAs the adobe block is laid window and external door frames are constructed and secured to the wooden framed blocks described above. These must be level and plumb (straight up and down) both left to right and front to back. 8x10" headers are installed over each external door opening. These should overlap the adobe block by 15" on each side.
Straight, Plumb, Level and SquareIt is obvious that in building a house it is essential that one focus on assuring everything is straight, plumb, level and square. And there are a number of tools designed to enable the builder to do that. Obviously four and six foot levels, plumb bobs, chalk lines and the transit. There are formulas to assure a corner forms a right angle and that a rectangle is true. The point is that there are a number of tools at our disposal. It is up to each of us to be as accurate as possible in their use. "Good enough" just isn't good enough. And paying attention from the very beginning pays big dividends. A level footing makes each step thereafter (laying concrete block, adobe block, the bond beam, etc.) that much easier.
The Bond BeamJust as the footing ties the house together at its base, the bond beam ties it together at the top. Once the adobe block is laid to the appropriate height a form for the bond beam is made and rebar is laid much as for the footing. The bond beam is a concrete collar about six inches thick that is laid around the entire building. Periodically a piece of Styrofoam is inserted to provide a channel for the electrician to avoid having to drill through concrete to run electric wire. As the bond beam is poured L-shaped threaded bolts are inserted periodically and at the corners to which pressure treated 2x12" planks are later attached with washers and nuts around the full perimeter of the house.
Building the ParapetsParapets form a border around the roof. They are about two feet high, six inches wide at the bottom and four at the top. They go around the roof with about a twelve foot opening to permit water runoff.
Framing the Internal WallsFollowing the house plan, the internal walls are laid out using a chalk line to mark their outline on the floor. This will outline all rooms, closets, doorways etc. The framing is of 2x4" construction, ( 2x6" where necessary to accommodate plumbing) 16" on-center. All doorways are appropriately framed. Once again, level and plumb are essential in doing the framing. A little extra time spent in assuring that the framing is measured properly, level and plumb will pay real dividends when it comes time to install the wall board, the pre-hung doors and the bi-fold closet doors.
VigasVigas are essentially untreated Ponderosa pine logs which, through the cooperation of the forest service, Habitat is permitted to harvest to use as an attractive roof support system. They are left exposed in the ceiling of the house and are an attractive, traditional design feature of local homes. Before they can be used they must be stripped of bark with a draw knife. Before being installed they are allowed to dry for a period of time to reduce their weight and to reduce shrinkage once they are installed. As they vary in size each requires tailor-made blocking to assure a uniform surface on which to lay the ceiling boards.
Laying the Ceiling BoardsThe boards that will form the ceiling are next laid across the vigas. As the boards are laid it is important to remove any high points in the vigas so the boards can be laid as evenly as possible. The boards should be parallel to the internal walls. It helps to periodically check from inside the house to assure that is the case. It may be necessary to make adjustments as you go along. Snapping a chalk line across the vigas helps to assure you are not getting too far off.
Finishing the RoofOnce the ceiling boards are laid, 11" thick fiberglass insulation is installed and framing is done to provide a slope from one side of the house to the other to assure water runoff. Crickets are installed in the corners to assure water does not settle there. The framing is then covered with a layer of OSB and then a thick black water proof membrane is installed. This is called a brai roof. This is then painted silver to reflect rather than absorb the suns rays.
In order to avoid water damage the wall board and internal doors are not installed until the roof is completed and the windows and external doors are hung.
Installing the WallboardOnce the framing is done, the wallboard is hung (where appropriate a special water-proof board is used, ex. around the tub enclosure). Before beginning it is necessary to assure that there is sufficient backing to which the wall board can be attached. It is also helpful to mark the location of each stud at the top and bottom. This will make it easier to assure hitting a stud when screwing in the wallboard. The wallboard is hung horizontally leaving a small gap between each sheet for expansion. Screws are driven in so as to be slightly recessed but without breaking the paper surface.
Hanging Internal DoorsHanging the internal doors requires assuring the door is level and plumb both left to right and front to back. It is important to test constantly to assure the door opens and closes properly. This is a time consuming job that requires a great deal of patience.
Preparing the Outside for PlasterBefore the outside of the house can be plastered the house must be insulated, covered in tarpaper and then with heavy duty "chicken wire". Each is nailed directly into the adobe blocked using long nails designed for that purpose. Lath must be applied to all corners, around windows and doors and on the top of the parapets. In applying the wire and lath it is necessary that it be tight and nailed firmly as it serves as the anchor for three layers of, somewhat heavy, plaster that follow. All the windows must have been installed. The frame for each is first covered with a water proof membrane. The windows and external doors are then hung. Once again a water proof membrane is used around the window frame to make it water tight. Lath is then installed around all window and door frames. A similar approach is used on the tops of the parapets.
Plastering the OutsidePlaster is applied to the outside. The plaster is comprised of an appropriate mixture of sand, Portland cement, and lime. Once it is applied it is floated and then, using a small rake-like implement, scratched. This must then dry before a second coat is applied. Once sufficiently dry a color-coat is applied.
Plastering the InsideThe perimeter, inside walls are adobe and the framed, inside walls are plaster board. The adobe walls are covered with "chicken wire" a lighter gauge than used on the exterior. All wood surfaces in the adobe wall are covered with tar paper to avoid water absorption and lath is placed around the vigas where adherence can be a problem. All surfaces with which the plaster may come in contact are covered with masking tape. The walls are then plastered permitted to dry and a finish coat is then applied.
Painting and Installing Cabinets, Lighting and Plumbing FixturesOnce sufficiently dry the walls are painted. The floors are cleaned and painted and the cabinets and lighting and plumbing fixtures are installed. A word about installing cabinets. If level and plumb ever had meaning it is especially true in the installation of cabinets. Adobe walls are somewhat irregular and, just as in hanging the doors, it takes real skill and patience to assure a perfect fit.