Structural Concerns with Adobe

Quentin Wilson and Associates, specializes in solar adobe design and construction. He grew up in the South Valley of Albuquerque, New Mexico where he watched adobe bricks being made. In the fifth grade, he made miniature adobes on cookie sheets in his mother’s oven in order to construct house models for a class assignment. By age thirteen he made full-sized adobes in the back yard and ruined the grass. Later, he traveled a bit, went through the Army, and graduated eventually from the University of New Mexico with a major in physics, minors in math, chemistry, and education in 1970. After teaching high school two years and community college math for three more, Quentin moved into professional solar adobe construction in 1976 as the Project Manager and Instructor for the Sundwellings Demonstration Project at Ghost Ranch, Abiquiu, NM. He became a licensed general contractor in the State of New Mexico in 1982. He has been building homes and teaching seminars and workshops ever since. In the fall of 1995 he established and taught the full-time Adobe Construction Program at Northern New Mexico Community College. His website, quentinwilson.com, lists the course schedule and many other resources related to working with adobe.

Q: I have designed and will be building a new Sala for a permaculture school in Chaing Mai, Thailand in 2013. We will be using adobe bricks made with a mixture of clay, sand and rice husks. For speed of construction and financial constraints I have opted for a metal roof over steel scissor trusses. My question: What is the best way to fasten the scissor trusses to the adobe walls? The walls will be two bricks wide so will be about 16" or more thick. For floors we have embedded iron wood in the walls and then the floor joists are attached to that and then cobbed in. Do we do the same with the steel trusses.

A: Iron wood would work nicely if it can be arranged to form a bond beam that runs continuously around the top of the building. This is sometimes called a ring beam or collar beam but the purpose is always to spread the load of the roof and provide a point for anchoring roof support members. The thickness should be at least 5cm but better would be a scheme of two 5cm layers which can be lapped at the corners to make really strong corners. It should be at least 25 cm in width and placed so that it bridges across the two widths of adobe. 40 cm would be even better as it would cover the two widths completely. If ironwood is hard to come by in such volume, bundles of staggered bamboo has been known to work just fine.

Now, so that the light weight roof structure does not lift off in a wind, it would be good if not imperative to have a couple more courses of adobes on top of the bond beam between the scissor trusses. You might want to think of some way to isolate the steel trusses from the adobe and any cob used since earthen materials can have a bit higher moisture content than is desirable for contact with steel. You might also want to think of some sort of a tension path from the bond beam down to the foundation. That could be done with wood strips, steel straps, nylon straps such as used to bind loads on pallets, bamboo or rebar. It can be embedded in the wall if there is a continuous cavity between the wdiths or it can be on the interior or exterior surface. Perhaps the weight of the adobes above the bond beam will be sufficient. I just don't know about your weather conditions.

Having had some experience with a tin roof over my head in the summer heat, I can't get to excited about the thought of direct sunlight raining down on the roof. Any insulation you can think of will be worthwhile: reeds, grass, fiberglass, layers of woven floor mats, thatch, thatch without the tin, bamboo bundles, ...

Q: Have you ever seen or built or designed an adobe building that had cantilever extensions of rooms or spaces that are on the second storey? I know that adobe has a powerful compressive strength, but can a cantilever be built and made from adobe? If not from adobe, can the cantilever extension be built from the supportive wood on the roof and have like a hang, in front of the building from which we can built upon?

A: Adobe does not do well in a cantilever situation unless very small steps are taken at each course. To cantilever out 12-inches would require about six courses of 2-inch cantilevers and six courses is 24-inches. Then there would be an overturning moment that would try to have the adobes roll over and drop.

Perhaps a cantilever with beams that are sized appropriately for the load and the lever arm of the cantilever and a counterbalance at the opposite end of the beams. There are cantilever schemes and calculations to be found in timber frame handbooks. Try to stick with adobe and perhaps keep your walls in a straight vertical line which makes it easy for the first-time builder. Do a second story on your third building and a cantilever on your tenth when you will really have a feel for the material.

Q: When building an adobe home, is it necessary to install gringo blocks and rough bucks? Is it possible to somehow leave an opening and only use Lintels on top and maybe screw the door frame directly into the adobes? I am planning on leaving the adobes exposed inside and out, and don't want the gringo blocks visible.

A: Sure. I did it. Once. We used 4" x 10" door frames so that we did not have to worry about their warping over time. The door frames/jambs went in first and we anchored them to the foundation and as the wall went up used steel straps in the mortar joints attached to the back side of the frames/jambs. We left a finger's width airspace at the top of the jambs before the lintels went in to allow for any settling of the walls. Filled the gap with fiberglass insulation and put a little trim board over it. Screwed some long lag bolts through the top 4.x 10 into the bottom of the lintels. The exterior doors were custom built, three inches thick. It took me a while to fit them into the jambs and mill and attach the door stops. Hinges of course were oversize. Doors slam and doors of this size exert a ferocious impact force on the jamb. Hence the 4x10's. The interior doors were 1-3/4" standard exterior panel doors and were a bit easier to fit into the jambs. The windows were Hurd. At that time the standard wood frames that Hurd used were nearly the equivalent of 2x 6" clear fir. They screwed directly into the adobe walls with 4" or 6" deck screws. Windows don't experience the impact forces so it is simpler.

Later projects we went back to solid gringo blocks downsized a bit. Then we could plaster over them and tool them to look like the other adobes. Rough bucks are part of the High Speed Fast Moving Don't Look Back System Using Speed Leads wherein the rough bucks are set up before the walls go up. Then the adobes are laid to the string and bump up against the back of the door and then window bucks saving the mason having to painstakingly create each opening straight and plumb. This could work for exposed adobe walls. If the rough buck is 2 x 6 and the door jambs and window frames are made for 2 x 6 walls then a trim strip can attach to the jamb, held back 3/8" and scribed to the adobe to cover the buck and the finished product looks good. It also preserves an airspace between the bucks and the jambs where the shims go and by removing the trim strip access is available to the shims at a later date if the door jamb needs to be adjusted. I always use screws rather than nails when attaching the rough buck to the gringo blocks and the door jambs and window frames to the rough bucks. That allows changes or adjustments later.

Q: I am living in a adobe home with 16" walls, built about 50 years ago in Tucson, Arizona. I would like to add a porch to the front of the home. How could I anchor the porch to the wall?

A: Possibly there is a bond beam in the wall just under the interior vigas or beams. If it is wood, long screws through a ledger plate will anchor the ledger plate to the wall and the porch structure can be attached to that. In truth it should just be called a ledger but lots of people add the "plate." If there is no bond beam then you need to drill through the adobe wall and run all thread through the wall and secure it on the inside with with 4" x 4" plywood with steel washers on that and then nuts and steel washers and nuts on the exterior. Probably about every three or four feet. This can all be chiseled into the wall and plastered over to hide them. The ledger should be two or three inches thick and have a depth equal to the depth your porch roof support members which can be attached to the ledger with steel joist or beam hangers. The joists or beams can also be placed on top of the ledger.

Q: We are thinking of purchasing an Adobe home in Cave Creek, AZ. The lintels above the sliding glass doors (x 4) and the windows in the front of the house (x 3) have extensive termite damage and need to be replaced. How difficult is this going to be to get done, how costly do you think it will be?

A: It is not difficult. Remove half a lintel from one side with saws, chisel, hammer, gumption. Slide in a new half lintel and tap in shims and/or damp dirt mortar to take the load of the adobes above and transfer the load at the ends to the wall below. Go to the other side and remove that half and replace it. Then drill through both halves every sixteen or eighteen inches and bolt together will 3/8" or 1/2" all-thread and 1-1/2" washers. You might want to bore or chisel out a pocket to hide the washers and nuts and then fill with wood dough. $150 to $300 labor per lintel plus the cost of the new beams. Normally termites do not get wood that high in the house but everything in Arizona these days seems to operate at the extremes. Consider a non-toxic treatment such as borate based salts.

Q: I am planning an adobe wall. My question is if I have to include the stem wall height in the wall height used for calculating height/width ratio or just the adobe part? Say my wall is 0.3m thick, I can build the wall 3m high. Do I count this 3m from outside floor level to top or from top of stem wall to top?

A: As best as I can understand the New Mexico Earthen Building Code, the height to thickness ratio applies to the adobe wall from the top of the stem wall to the bottom of the bond beam. Wording of the Code varies over the years. A clever person could use this interpretation to achieve a higher ceiling level. I personally used the ratio to figure the total distance between the floor and the bottom of the vigas or beams. The ratio also applies to cob and rammed earth although many rammers operate more in the range of 6 to 1 height to thickness ratio.

Q: The front of the house has planters with dirt at the brick wall with evidence of 1-2 inches of coving, should I worry about this before buying? After buying it I would removed the soil to make sure the bricks are not exposed to moisture from the soil.

A: Good solution. 1-2 inches of coving is not desirable but is not a fatal flaw either. Usually adobe mud can be packed into the coving once any loose particles are removed and the wall will be as good as new or nearly so.

Q: The windows and door frames are made of steel with the steel extending into the brick in locations such as at the top of the window. If I wanted to replace the single pane windows would I have to mess with the brick? The steel is showing some rust, will these have to be replaced? With removal and replacement of bricks? Is this impossible or just super-expensive?

A: You might check with a local, experienced glass company or window company. Some window manufacturers such as Crestline and Anderson make replacement windows that fit into existing openings. Sometimes the glazing can be removed and replaced with double glazing or a well fit storm window can do the job. Alternatively, with steel windows the glazing can be removed and then the steel frame cut with a reciprocal saw in a couple of places to collapse the framing inward - hourglass style - and the fins can be withdrawn from the masonry. ..... Unless the Weir Brothers went the extra step and anchored the fins into the bricks in some way. They may have nailed or screwed the fins into wood lintels or used some other technique in concrete lintels.

Q: We want to attach a 16 X 20' carport to our adobe home built in 1938 in Tortugas, NM. What is the most secure way to attach the ledger plate?

A: I would bolt through the ledger and wall with 1/2" all thread. Inside the house you can make 4" x 4" plywood washers of 3/4" ply. A large washer on that and then the nut. All of that can be chiseled into the wall and plastered over on the inside. A bolt about every six feet would be about right. I would also consider a 4 x 4 post on a concrete pad under the ledger about every twelve feet to transfer some of the load to the ground.

Q: I recently purchased an adobe home in

San Diego and want to attach a patio cover over part of the south facing exterior wall. How would it be best to attach a ledger to the side of the house? The walls are 12" thick adobe.

A: The best way is to support the ledger with vertical columns at 8- to 10-feet on center on spot foundations four- to six-inches above ground level. The ledger is then best anchored to the wall every four feet or less with 1/2" all-thread bolts through the wall backed up on the interior with 4-inch square or larger plates of 1/4" steel or 3/4" plywood with steel washers in chiseled pockets that allow for the plates, washers, nuts to be plastered over with mud or whatever matches the interior plaster. Should the interior wall be exposed adobes, then use mud troweled and tooled to match the brick pattern. The columns can be omitted but I always used them to lessen various loads on the adobe wall. Should the ledger be located in a position where it is not feasible to drill through and attach inside the wall, then your creative solution will be as good if not better than mine.

Q: I have a 15'X4' wall covered in stucco. It is starting to tilt, so far about 3-5 degrees. I just found out it is adobe underneath. Is there any way to retain this so as to not tear it down?

A: The usual fix is to add a buttress or two on the side toward which the wall is tilting. I have done just that on my own adobe wall.

Q: My parents home is 100+ years old. Some of the interior walls are adode. The wall above a door way has a crack, on either side, that seems to continue to separate. Is there a reasonable method of repairing or reinforcing this situation? Not sure how long this has been apparent. I am concerned of the structural integrity of this wall, but mostly for my family that will continue to live in the house.

A: Cracks on both sides of a door lead to the thought that there might not be a lintel over the door. A proper lintel would be 6" by 10" wood or concrete or stone and it should extend 12" or better yet, 18" on either side of the door to distribute the weight of the wall above the door onto the adobe bricks on both sides. That is the modern code version of a lintel. In historic houses it is often less but works fine over time anyway.

It is not easy, but a lintel can be added after the fact by chiseling half way into the wall and installing half a lintel with shims of wood and/or dirt to support the adobes above and transfer the weight to the adobe walls at the sides. Then, around to the other side of the door and chisel out the other half lintel space to line up with the first and then shims again. With the two halves in place, bolt them together with three or four 1/2" all thread rod. It's that easy. It's just hard work but you will be done in 5 hours except for plastering over the wall unless you want the lintel to be exposed as some people do.

Q: I have an Adobe brick house, I would like to know if it is possible to remove the outer brick leaving the inner wall and replacing the outer brick with a concrete block or brick, the home construction is two side by side rows of Adobe block the blocks measure 16 inches long 8 inches wide 4 inches thick, the header is poured concrete where the roof joints attach?

A: You can certainly do that and I would recommend CMU over fired brick. CMU can be core filled with insulation to reduce heat loss or gain through the wall. However, that is a massive amount of work and I am not sure why you would want to do that.

The Adobe brick is falling apart, I do not know what else to do in order to preserve the value of my home, would you have any suggestions?

Okay, that's a situation where I will allow you to replace the adobe with CMU. It might be best to have a skilled professional do the work and it should proceed with short sections of the wall to make sure that you do not have collapse. The CMU's should be gap-toothed to allow sewing in the next section of wall. Or, it might be apparent to the person doing the work that large sections of wall can be removed and replaced without problems. In true double walls such as this, called two widths, it is customary in brick, CMU and adobe masonry to tie the two walls together at several levels of coursework as the walls go up. It might be as simple as turning adobes sideways to bridge across the two widths or it might be steel strap ties, or rebar butterflies or Durowall, the ladder-like 10-gauge wire that is made for reinforcement in CMU walls.

Alternatively, if the walls are not plastered on the exterior, you might consider patching the adobe where you can - it can be as easy as pulling out deteriorated chunks and replacing them with stiff adobe mud and then once dry, putting standard three coat, cement based stucco on over stucco wire lath. Do not use Western One Coat or any system (Drivit, Sto) with an elastomeric final coat as those products have nearly zero moisture vapor permeability and will hold moisture in the adobe wall. Also, do not use roofing felt, Jumbo Tex or any other vapor barrier material under the wire. That is standard practice in frame houses and is specified by most building codes but should be avoided in masonry houses.

Q:  I have a close friend who lives in Orekhov Ukraine. She has a 60 year old home, constructed of brick with 10 inch adobe walls for the interior. It utilizes a gas heater box with a central heating wall. The electrical and water service are added years after initial construction. To be blunt the house is a mess, to little electrical supply, water pipes freeze in the winter, walls interior and exterior are all cracked and not straight. I would like to gut this house, leaving the brick frame intact, then frame interior with wood and add proper heating, electrical and water services. Can I remove the interior walls without causing structural damage?

A: You can easily remove the interior walls as long as they are not holding anything up. If they are holding something up, just be ready and nimble to quickly put the new structural wood frame interior walls into their place. I am guessing that the climate in the winter is moderately cold, with high humidity, often overcast and not a lot of sunlight. Let's say something like Toronto. I hope you are thinking about abundant insulation for the exterior walls and the roof. Insulation and tight windows and doors will give the most improvement in the thermal performance and the feeling of comfort for the time and expense invested.

Q: How might you attach a interior adobe wall to a exterior straw bale wall. My ideas: rebar pins at 2ft intervals embedded in mortar joint, partial concrete bond beam w/rebar poured in a carved out channel in straw bale wall?

A: The bond beam is a viable method. Rebar does not get much of a grip on adobe. I would consider CMU ladder reinforcement commonly known as DuroWall at least three feet into the adobe wall and five into the straw two-foot intervals. It is bendable so if courses are not perfectly even it can be bent to accommodate. If the straw wall is already up, that won't work so back to the rebar and prayer.

Q: My husband and I purchased a two story Pre-1880 adobe home in Trinidad, CO. Extensive repairs are needed throughout the home to include new roof, plumbing, windows, heating - you name it and we had planned on repairing or replacing it. The adobe is in good shape and the structure appeared very solid and sturdy although we couldn't see exactly what we were dealing with until we continued to remove obstacles. . The more we took out, the more we had to put in the landfill because of the years of neglect. The house has been stripped down to the adobe and wood studs. The floors were uneven and we found this to be caused by years of wear where the 2nd story floor beams were attached straight into the adobe and had loosened. Our contractor has contacted eight structural engineer companies located nearby in Pueblo to address the problem and only one will consider looking at the home because they say that there is too much liability connected with a two story adobe house. The concern is that the structure cannot bear the weight of the roof and large snowfalls which will cause the exterior adobe walls to fall outward and the house to collapse because there is nothing securing the walls. We are waiting to hear back from the one structural engineer that has experience with these types of homes. The home is listed on the historical registry of contributing properties but is not eligible for grants. At some point we are going to have cut our losses and it currently appears that the house will have to be demolished if we cannot find a way to make it 100% safe. Have you heard of problems of this nature and can you recommend any way to proceed?

A: Too bad the engineers of Pueblo cannot access basic published strength of materials numbers for adobe. Adobe walls are one of the most powerful load bearing systems that can be used in home construction. Two-story construction is and has always been permitted by the New Mexico Earthen Building Code. Adobe now has its own page or two in the International Residential Code but that may allow only single-story construction.

Most adobe bricks, old or new, have a compressive strength of 300psi. Taking five-percent of that and if the coursework is halfway decent the top of the wall can bear close to fifteen-hundred pounds per linear foot. That's using a working load of 30 pounds per square inch  on a ten-inch wide wall by twelve-inches. I don't know of any other building system that comes close to that. It's the power of monolithic.

Adobe bricks are expected to have a minimum modulus of rupture of 50psi. That is low for any material but the whole purpose of masonry wall construction is to avoid subjecting materials to flexure which is what MOR measures. Adobe bricks are required to be fully bedded in mortar so that they are not suspended over air space whatsoever as in the case of the MOR test: https://en.wikipedia.org/wiki/Flexural_strength

New Mexico two-story code-compliant construction calls for a 14-inch wall on the first story and a 10-inch wall on the second. If the wall thickness does not step back for the second story then the thickness should be 20-inches for both stories. An old house in Trinidad likely used sixteen-inch-thick walls for both stories. Since Biblical times it has been known by masons that adobe walls are very sturdy if the height is limited to ten-times the width of the wall. Houses with interior adobe walls interlocked with the exterior walls gain further strength from that. Just like a beehive.

And then, 135 years standing is proof far beyond any calculations or laboratory tests that your house will not fail structurally. I would expect that there would have been a few heavy snow storms during that time. On the other hand, 100% safe is a difficult standard for any type of home construction. You might have to settle for 99.973%.

The second story floor beams would hopefully rest on a bond beam that went all around the structure. This was almost always wood in the 1800's and early 1900's and that is fine and meets the modern code. Otherwise there should at least be a wood plate under each beam or better yet a plate that extends under all the beams to spread the load. If none is present a 2 x 4 or 2 x 6 can be situated in a channel cut under the beams and then shimmed with wood and adobe mud to transfer the load from the beams to the plate to the adobe. Then the process can be repeated on the opposite side of the wall so the total plate is 2 x 8 or 2 x 12. Also, it is hoped that there is a bond beam under the roof structure to spread the load and tie the building together at the top. If it is missing, it can be added as described for the floor system above.

Incidentally New Mexico has the Existing Historic Earthen Building Materials Code. The name may change a bit as a result of submissions to the Construction Industries Commission the 5th of this month. Essentially it accepts existing materials and allows repairs and additions to be built in the same manner as the original construction.

Q: Our 1896 2 story Adobe farm house near Carrizozo NM is one room wide with 3 rooms in a row, one after another, on each floor. Rooms are 16 feet wide between load-bearing walls. Adobe walls are 18" thick and rest on dry stacked sandstone . The second floors are very very bouncy. The floors are wide butt-joined pine boards, lacking subfloors, nailed directly to true 2" x 6" ceiling joists. Joists are 16+' long, average 16" between them, with wood cross-braces. Joist ends are embedded in the load bearing walls over a 1"x wood plate but typically there are small mud-filled gaps between joist end bottoms and plate. I do not know how far the joist ends extend into the walls. My plan is to insert one 6" x 6" x 14+' wood beam (girder) into the tops of the non-load bearing adobe cross walls, just below and perpendicular to the bottom of the ceiling joists, in each first floor room. The girder ends will extend 18" through the walls, resting on short horizontal boards (plates). Then I will fasten the bottom of the joists to the girder and install a subfloor. This will cut the joist spans and add support. Does this sound OK? Will the 18" thick non-load bearing adobe walls bear the weight of the girder and the joists and floor on top of it? Or do I need to add columns to help bear the weight of the girder etc?

A: Adobe walls can certainly hold up to the 6 x 6 x 14' if there is a 4" or thicker plate below them to spread the load on the wall - minimum 3' length. Better yet, a full, retrofit bond beam. 2 x 6 @ 16" on center even if true 2" x 6" from the 1896 era are undersized for a 16' span You could also beef them up by placing a 1 x 10 on each side of the 2 x 6's with a cap across their bottom sides to conceal the 2 x 6. This type of sistering is actually fairly common in old structures especially those where the upper floor was not originally expected to have much occupancy. This might or might not be easier than your girder idea, but it would preserve some headroom below.

Q: My grandparents built their home in the 1940s out of Adobe room by room. My mom was small and she remembers them first living in the front room and everyday my grandparents making adobes outside and building on to the house until it became the 1800 sq ft home it is now. The last 300 were added on later with brick for a laundry room and other modern amenities. In fact the entire little community including the church was made from Adobe originally. My mother inherited the house from her parents. Unfortunately the coping has given way on the lower half of the house, the adobes have swollen and the sand is exposed. What steps would you recommend we take to patch up the walls in our Old Adobe home that will prevent future structural damage or further weakening to the Adobe bricks?

A: I am sorry to hear of the troubles you are having with your house but I am glad to know that you want to preserve it. I use the word coping to refer to the top of a wall or parapet. Perhaps you might be referring to the plaster on the lower half of the house. Also, if adobes swell it usually mean that they have been made with an expansive clay such as bentonite that swells when it gets wet. There is bentonite around Fort Worth but I have not heard of it around El Paso. Therefore, I am not sure why your adobes would swell. Sand is actually the most basic and largest part of adobe. In the best bricks it is about %70 and clay is about 30%. Adobe bricks, mortar, plaster and floors can be made with higher content of clay but then the mixture will crack as it dries out. Finely chopped straw stops cracking in the higher clay bricks. When you say that the sand is exposed I am again not quite sure what you are seeing.

What you are talking about seems to me to be a problem of rising damp which is moisture that comes up through concrete foundations and migrates upward through the adobe walls. That is a common problem in the Rio Grande River Valley area and often salt crystals are deposited on the surface of the adobe as the water evaporates and leaves behind the chemicals it has picked up as it rises. This manifests as white crystals on the surface of the walls and is called efflorescence. It is a problem for all types of masonry walls and not just adobe. The solution is usually to plaster with a material that breathes. That is a material with moisture vapor permeability such as just plain mud plaster, lime plaster or even what you might hear only from me is modern cement/lime/sand plaster directly on the adobe with no paper, plastic, tar or any other material that would retard the migration of water out of the wall. There will still be efflorescence but the wall will be dry whichever covering you might choose. Most preservationists do not agree with me at all about the standard stucco but I maintain that we can find values of 5- to 6-perms for the material in trade literature and that is not zero.

A man who bought one of the adobe homes in the area fixed his around 10 years ago. After chatting with him, he said that his key to success was mesh metal netting and concrete. Another gentleman also recommended the mesh metal netting and lime plaster. He used the method to restore some homes and a garage.

The inside wall is classical rising damp. It looks to me as if the interior plaster has a coat of tan paint. If it is a gloss paint, it is much more impermeable than flat or satin paint. Flat paints are always better for interior walls in adobe homes. For the time being I would suggest removing plaster and paint from around that corner up to and a few inches beyond where it has darkened from moisture. That will allow the wall to dry out. It may take several months. I was just in a house with worse problems in Santa Cruz, NM next to Española and the woman who owns it had fans going to accelerate the drying. If plaster is removed to a fairly straight line revealing the adobe bricks and mortar, it will be interpreted as a "truth wall" and not so much as failure of the plaster or an eyesore or worst of all, poor housekeeping.  Once the wall dries, the area can be replastered with gypsum based plaster such as USG Red Top or Structolite. A handy person can also replace the removed plaster with just plain mud plaster which could take a light coat of flat paint of the right color. Better yet, colored clay plaster such as is produced by American Clay in Albuquerque www.americanclay.com or New Mexico Clay  https://nmclay.com/aliz or best of all, hand mixed aliz plaster made from the right colored dirt found in your area. People who do this have their lives changed: as they drive along, they are always looking at cuts in the hills along the highway to spot dirt of a special color.

Outside the wall is just as it should be for the time being. With the plaster gone, the wall can dry. Part of the problem may be attributed to the low curb of concrete which appears to be against the adobe but not under it as would be the case if it were part of the foundation. Also, the concrete skirting (sidewalk?) around the building may be contributing to the problem. Both the curb and skirting slow the ability of the soil around the building to transpire ground moisture upward and evaporate it in addition to concentrating rain water. The curb and skirt appear to have been well done. Many times the curb begins to lean out and any rain that comes in horizontally is funneled against the wall by the curb. Skirting sometimes moves over time and ends up with its slope inward toward the wall and acts as another multiplier of moisture against the wall. These are just the things the Mexicans have seen time and again particularly where a building is right up against a paved street as is more often the custom in Mexico.

The building will certainly collapse in eighty or so years. That gives you some time to deal with the problem. Adobe is slow at anything is does so that works in your favor. For the time being take no action beyond considering removing another foot or so upwards of the exterior plaster. In your climate, exposed adobe walls will loose about 1" of thickness every thirty years from rain and wind. Other good news is that I don't see any coving which is where adobe begins to fall out of the wall at the bottom a little bit at a time due to rain, rain splashing, freeze/thaw cycles. Freeze/thaw is minimal at your location. It is a monster here up north in the snow country.

Cornerstones Community Partnerships in Santa Fe, www.cstones.org, has a nice restoration handbook that covers most of this. They are far more vigorous than I am in the campaign to eliminate cement based plasters on exterior walls. However we agree that you should hold off on the use of any poured concrete.

Q:  I work for an NGO in Mexico building houses for poor families. We plan to start using adobe for our next house (no. 108) and I am trying to figure the best way to attach wooden door and window frames in the adobe openings. Can you help? casitalinda.org

A: Bucks. Door and window bucks are the standard method of installing windows and doors in masonry walls. A buck is a wood frame that outlines the opening and has inside measurements that conform to the window or door to be used or better yet, the buck is a rough buck and the interior dimensions are such that a door or window can be obtained with a trim jamb that - once the wall is finished and the roof is in place - is inserted into the opening with nails/screws and shims just as would be done with the rough opening in a frame house. A buck - rough or finish - can be done with a 50mm x 100mm or 50mm x 150mm framing lumber or the 2 x 4 or 2 x 6 USA equivalents. This facilitates rounded corners - bullnose plaster around openings. Or the builders or owners might prefer wood that is equal to the width of the wall.

With rough bucks built so that the inside dimensions are equal to what a manufacturer would call out for the rough opening in a frame wall, installation of pre-hung doors and windows sash built into trim jambs the hanging process goes quickly and allows builders to use readily available pre-hung doors and fully manufactured windows.

My assumption is that the rough buck is built, stood up, squared and plumbed before the adobes go up so that it becomes integral with the wall. Window bucks are four-sided open boxes. Door bucks are three-sided but for convenience of handling with a bottom piece built with an eye towards removing it once the walls are up. As the coursework goes up, wood to masonry connections can be made every several courses using long nails or screws (150mm or longer) into the back of the buck such that the nails/screws are in mortar joints. Expanded metal lath laid in the mortar for 400mm or more can be bent up and nailed/screwed to the back of the bucks. Heavier metal pieces known as hurricane straps in the USA also work fine.

Most builders in New Mexico use gringo blocks which are no more than a wood frame of 50 x 100mm lumber made with the outside dimensions equal to an adobe brick. The gringo blocks are laid into the coursework to replace full adobe bricks at the back of rough bucks every four or so courses as the walls go up. The rough buck is then screwed/nailed to the rough bucks with fasteners long enough to go through the rough bucks into the gringos. The gringo blocks are filled with mortar mud before the next course goes up.

Over the rough bucks or trim bucks there needs to be a lintel. Wood, concrete, steel, stone. Don't let framers call them headers. This is masonry. Lintels should be the width of the wall or at least 250mm with a minimum depth of 150mm. (100mm depth in a pinch and where openings are no more than a meter.) Lintels should be long enough to have a minimum bearing of 300mm on the masonry on each side of the opening. The best laid lintels have an air gap of around 20mm between their bottom surfaces and the top surfaces of the rough buck. This allows for settling of the adobe mortar without the weight of the masonry above coming down onto the rough buck, or worse, the trim jamb.

Just suppose walls are already going up and there are no bucks in place. It is no real problem but it takes longer to affix trim jambs to adobe walls. I am sure that there are Mexican equivalent to the problem solvers. Number one is deck screws or gold sheetrock screws in a 150mm or longer length. A battery powered drill/driver will send them right through an undersized pilot hole in the wood into the middle of adobe bricks. Anyone who doubts this will be convinced when experiencing the process shows that the drill is barely able to do the job and is as heavily burdened as if the screw were going into wood. Texas Tacks also work. These are 60d nails which are 300mm long. These work will but will require an undersized pilot hole in the adobe which requires a long, thin masonry bit. Original Gorilla Glue works as do the foam in a can insulation/adhesive such as Dow's Great Stuff. These urethanes stick to everything: adobe, wood, kids.

So, back to the beginning. High Speed Adobe Construction begins with speed leads. These are story poles - one at each corner of the building. Plumbed and braced in place they outline the building with the mason’s strings that are run between them to guide the coursework. Tops of courses can be marked with pencil beforehand to eliminate measuring after each course. With speed leads no master mason is needed. Courses should progress up with one course at a time being completed before the string is moved up to start the next course. No level is needed to keep openings plumb because the aforementioned rough bucks are in place and volunteers, owners, kids need only to bring the bricks in a course right up to the back of the bucks.

In your climate progress will be limited to 5 to 7 courses per day. Beyond that the walls will get a wobbly because the mortar has not had time to dry. Humid weather will cut daily production back also. Walls are capped with a continuous bond beam. Both concrete and wood are permitted in the USA adobe codes. A wood bond beam made up of several layers of 50mm thick by 250mm wide lumber will go up in two hours with a crew on the ground cutting and a crew on the wall nailing. A concrete bond beam will take longer but Mexicans are virtuosos of concrete construction. The wood bond beam readily accepts nailing, screwing or strapping to attach the ceiling/roof structural members.

Someone in SMdeQ must have a copy of P.G. McHenry's book, Adobe, Build It Yourself from the University of Arizona Press. About $25USD on Amazon. It covers everything and has great illustrations. Written around 1974 it is still current and has not been surpassed.

Q: We have a house built in the 50s and its exterior is made of adobe. In the back we have a small laundryroom that also has a door leading to the backyard. We are planning on knocking down the exterior wall and extending the laundry room 5ft out and also creating another bedroom. Our concern is, is that the wall we plan on taking down is adobe wall and were afraid that if we take it down it will cause structural damage to the other two walls. Is it possible do to this without causing structural damage to the other two existing walls?

A: If the wall you want to take down supports vigas or beams or joists then it is more difficult. You then have to make provision to support the roof/ceiling support members with a large beam supported by posts that rest on a solid foundation. It the wall is not supporting the roof/ceiling then the job is much easier. You might have to add a buttress or pilaster to keep the remaining wall from wobbling.

Q: I cannot find the answer to the use of castillos (masonry star fort) to strengthen an adobe house.  These are vertical (from floor to ceiling) poured concrete about 8in X 8in.  Do you recommend using this or just steel rods without concrete? I guess my question is what do you recommend to use in the adobe walls to make it earthquake resistant? 

A: I am not familiar with castillos as you use the word. Mexicans and Californians use vertical posts of concrete reinforced with vertical rebar and often tied into the adobe wall with horizontal rebar. Rebar alone in adobe walls is of little structural value since adobe does not grip the rebar tightly as does concrete. In New Mexico, we are fairly casual about earthquake resistance and do nothing or occasionally place Durowall - the ladder shaped 10-Gauge reinforcing used in brick walls - horizontally about every second to fourth course of adobe bricks.  Our quakes are minor here. In places like Chile, Peru, and California greater measures are in order. It's really a job for an experienced engineer to design a system that is appropriate for a particular location and the type of motion induced by an earthquake. The world’s center of anti-seismic knowledge is the Engineering Department of the Catholic Pontifical University in Lima Peru. There are many qualified engineers around the world. If I know where you are located, I can be more specific.

Yes, the 'castillos'  are the vertical  posts of concrete used often in Mexico.  I am building in Baja about 3hrs south of Ensenada. I have decided to go with what my builder is recommending for the shorter part of the project.  But for the portion that will be two story I am going to do the vertical concrete with the half-adobes missing to make the concrete tie in better with the adobe plus horizontal rebar.

A: Before my adobe constructor arrived, I worked on the foundation and also have vertical steel rods (called castillos in Mexico) - four at a time to be filled with cement.  I am now worried that instead of strengthening the walls and making the whole structure more solid, it may actually do the opposite?? because my adobe guy is telling me that he has to make like a groove so the adobes fit a little bit inside the cement because the adobe will not adhere to the cement.  He would prefer to remove 3 rods and leave 1 to place the adobes with a hole that would go there and use that as the wall strengthener. What do you think?  Would you use cement vertical pillars for an adobe construction?  If not what would you use? The adobe house I grew up in has cracks from the earthquakes throughout about 100 years.  It is in pretty good shape but I wanted to make this one with stronger walls.

A: Your adobe person might be right. The concrete pillars are an interruption of the continuity of the adobe walls. On the other hand, adobe is so good at sticking to things, mud mortar and cement based mortar will stick to concrete as well as mud and cement mortars stick to adobe bricks. If the adobes go in first, just leave out half bricks when they occur next to the concrete pillars and when you pour the concrete it will flow into the walls with a little extra formwork. On the other hand Californians and others sometimes just build a post-and-beam structure of reinforced concrete first and then infill the spaces with adobe. Worldwide, the current thinking in best practices as I interpret it is to wrap the exterior of the building with steel mesh such as very heavy duty stucco reinforcement or the very heavy orange plastic webs that we see around highway construction zones for traffic control and safety. Then, one stuccos over and through the mesh. The concept is to produce a building that gives the occupants a few more seconds to get out of the building in a catastrophic event. The building itself might not be suitable for habitation afterwards. Sort of the technique that Volvo pioneered where the car is totalled in a crash but the occupants survive.

Q: We own an adobe home in the historic section of Tucson, AZ. Years after it was origionaly built they added a wooden framed addition to the back of house to add a bathroom and kitchen. This old wooden framed addition is badly damaged by termites. Our plan is to demolish the wooden addition and rebuild the addition in adobe. Our question is how to best attach the new adobes to old adobes? The foundation on the old house is primitive. Large rocks mixed in cement. Our "new" foundation for the additon will have to be built to modern code. So it's going to end up being on basicly two separate foundations. I am worried that where the old adobes meet the new adobes will forever have separation and cracking issues over time. Any suggestions on how attach the new work to the old to help stop this from happening?

A: Have a glass of wine or two and proceed. Nothing can stop masonry walls from small separation cracks where two separate structures join. That's why the masonry industry has developed expansion joints of various types. If you are going to stucco the finished product you might consider a metal expansion joint. I don't care for the looks of them so I just stucco over the two sections and keep some butyl caulk handy five years later when cracks appear. Sometimes they do not appear. You may have a really good foundation on the original building even if it does not meet current code. After all, it has had over a century to settle into its final shape. But then you might have cracks as the new, code-approved foundation settles a bit or the mortar joints in the new wall shrink a millimeter per course. Some people pull half bricks out of the old wall and sew new bricks into the pockets as the new wall goes up. That's the best method but it will still crack. Other people drill six- to 12-inches into the existing wall and insert a 1/2- or 3/4-inch rebar and bury two- or more-feet of it in the mortar joints of the new wall. But it will still crack. Reward yourself with another glass of wine. A hundred years from now observers of the two parts of the home will pronounce you a genius cracks or no cracks. 

Q: You answered a question about the circular arch window. You said that the arch needed a few feet of solid wall above the arch. In my situation, I have a 40cm thick adobe wall, and will place a 20cm concrete bond beam on top of the wall. How do you feel your recommendation of "a few feet of solid wall above" applies to my structure? In other words, how much solid wall above the arch is sufficient in my case?

A: With that concrete bond beam above the arch it will act as a lintel over the arch and will take up the load of the structure above. Therefore there would not be a need for any adobe above the arch. It would not hurt to thicken the concrete to the appropriate depth that would be needed if there were no arch.

Q: Is it possible to use metal vigas for an adobe structure? And if so, what could we use and what size would they need to be?

A: Metal vigas have been used in several adobe houses. Pancho Villa is said to have built a house that used car chassis for vigas. Steel bar trusses were used in an adobe house in Albuquerque to save money,They seem to be using trusses of rectangular tubing, nicely fabricated. Five by eight steel tubing would serve nicely as vigas in a flat or slightly sloped roof. Size really depends on the span between the walls and the spacing of the trusses. Don't do this without engineering from a steel fabricator or an engineer. Just arrange to have plates with holes drilled in order to bolt, spike or lag the trusses to the bond beam of the structure. This is not stuff that you will find at Home Depot.

Q I: presently have 5' high x 2' wide windows facing south. Is it OK to add further framing and reduce size of windows to say three sections? Also 5 years ago had a new roof which was a heavier gauge than old one; now I am seeing more cracks near roof.

A: Windows can - almost always -  be reduced in size by a competent carpenter or builder. Making windows bigger is often not easy. Metal roofs are popular because they are light. Even heavier gauge metal should not add enough weight to your roof system to cause problems. The cracks may be coming from another source.

Q: My husband and I are considering the purchase of a home in Carmel that is constructed in what we are told is the “Post-Adobe” style. The walls are made primarily of adobe bricks and held up by large timbers. The electrical is run through the timber’s and the roof is supported by rough hewn lumber. The building was originally constructed in 1948 and has had a few additions done to it over the years, nothing recent and all of which appear to also be done in a similar style.. If we remove an adobe section of wall, does the house framing remain structurally in tact?

A: If the structure is true post and beam with adobe infill then the wood bearing elements could be expected to hold the structure up if an adobe wall below is removed. However, over time there may have been some settling that would have transferred some or all of the weight of the structure above the beams down onto the adobe. I have done two small post and beam with adobe infill projects on my own home. I would be cautious about removing any adobe without closely watching/monitoring the wood elements to see if they move downwards. On one project the opposite took place and the adobe walls shrank downwards as the adobe mortar dried so there was a 3/8" gap between the wood beam and the adobe below. You can remove parts of the adobe wall and expect the wood beam above to bridge over the opening up to five feet. If the beam is sound, it will act like a lintel. Mainly, this all depends on the person who is doing it remaining vigilant to see if there is any movement of wood or adobe above the opening.

Q: I'm looking for some info on having an attached solarium/greenhouse to an adobe home. This will be a new structure in Tularosa ... using 4x10x14 bricks (14" width) ... that is, about 84" of adobe wall, +6" stem wall and 6" bond beam ... 96" wall.  A New Mexico Style Pitched metal roof adobe dwelling ... with the plank and beam ceiling. My question ... Greenhouses are notorious for humidity ... so I was pondering doing a veneer of dry stone on the 42' wall where the sunken greenhouse would be attached ... do you think this would mitigate the moisture into the adobe?

A: My experience with adobe walls in an attached greenhouse is that there is no problem with moisture. My experience goes back to the Sundwellings Demonstration Center at Ghost Ranch in 1976/7. Also my own home which has become very minimal in the plant inventory due to reasons other than humidity/moisture. Some study in the Pacific Northwest showed that adobe bricks are strongest - by a little bit - at 60% humidity. If the stone veneer is a moisture vapor barrier, then if moisture gets behind it, the bond between adobe and stone can be broken and the stone falls off.