Published 10/30/08
Dear Anselmo: Is it better to repair or replace a damaged adobe wall?
Contrary to popular belief, earthen structures are strong and resilient. Earthen walls can be cracked, crumbling at the base, rounded at the top from decades of exposure to snow and rain, or mushy at the bottom — and oftentimes they’re still stronger than a frame or mobile-home wall.
Moisture is generally the main culprit, but there can be other causes such as trees, wind, vibration from traffic, animals and changes made with modern materials. After the cause of damage is assessed and remedied, it is time for repair. There’s no use addressing the symptom without first stopping the cause.
If restoration is your goal, the first step is to cut out loose and powdered areas until you find hard material. Avoid the temptation to tear down the wall and build a new one, as this can lead to unseen problems. Also, the authentic antique look of the structure can be lost. In restoration this is a major mistake, since it changes your project from restoration to remodeling. In my opinion, this can rob the house of its historic integrity and hand-crafted beauty.
In the case of cracks, widen the crack by cutting at the edges. Later on, mud can be injected by various means. In the case of a crumbling base, cut out the weak and crumbling part of the wall. If there is extensive damage, cut out a small section (perhaps two or three feet,) rebuild it and let it dry for a couple of days. Then you can do another small section. This process can usually be rotated with other tasks, and it’s many times easier and less expensive than tearing the wall down and rebuilding.
When repairing plaster, remove the loose sections. Sometimes they’re obvious, and sometimes you’ll need to search for them by tapping the wall. You don’t need to plaster to a screen if you have the proper mix. All material cut out of the wall can be saved and used for the repair mix. This will almost always yield the perfect mix, no matter what type of repair you’re doing.
In all cases, thoroughly wet the areas to be repaired. This will give maximum bonding. Large holes can be filled with new blocks; choose blocks without asphalt or concrete additives to achieve the best bond. In general with restoration projects, avoid using concrete, metal or petroleum products. The rule is to try and match the original materials and techniques.
Anselmo Jaramillo teaches traditional adobe construction at Northern New Mexico College, avoiding the use of cement, metal or petroleum products. For the last 40 years he has been involved in restoration and new construction of earthen buildings, both in the United States and Mexico. Send questions or comments to rataoro@hotmail.com, or adobeclass.blogspot.com, or call 351-9924.