Adobe as Plaster?
Question: With my wife, we have recently established a private company in Ethiopia for an investment in eco-cultural lodge in Lake Tana area. As the lodge will be build out of Adobe (similar to some historical construction in Ethiopia), we are considering various construction technique options. Each lodge will be built like a small Ethiopian Orthodox church with wall decorations and paintings. We only use local material (foundations made out of stones, Adobe wall, and thatched roof). The main concern we have in designing is to stabilize the plaster (mud or other material) in order to preserve the wall frescoes we are planning to produce. Do you have any reference on how best to plaster Adobe/mud houses? What material is mostly recommended for interior plastering, keeping in mind that the lodges need to keep a fairly high standard of comfort.
Answer: The same mud that will make adobe bricks makes a good plaster if it is screened through a fine mesh of about 1/8th inch.
Exterior Plastering: the rainy season can be very wet and in order to protect wall frescoes on Adobe, stabilization of mud plastering (or other material) is a main concern.
Good overhangs of the thatch is the first defense. There must be something that locals use. Around here there is mashed up and fermented mixes of cactus and manure. Some folks rely on lime-based plasters.
A book on latex concrete technology has recently been produced (Albert Knott and George Nez, "Latex Concrete Habitat", Canada, 2005). Could Latex concrete or latex slurry be used to stabilize mud plaster?
You can add latex to mud plaster. Careful. If it is so waterproof that it does not breath, then water vapor cannot get out and large chunks of the plaster fall off. Experimentation with appropriate ratios for each soil is required. Make test samples of various ratios and plaster a half-inch thick on a board. Let it dry and set them out to get rained on to see what happens.
Moreover, the municipality of Bahar Dar and Amhara regional state in Ethiopia had very recently (19th of June 2005) agreed to lift a ban on mud house construction in urban areas. Yet, they would like to regulate such construction in order to maintain minimum standard for urban development (they don’t want to see slum types of construction in their cities). Is there any existing standard to which the Municipality and regional government could refer? Bahar Dar enjoys a warm climate with mostly uni-modal rainfall. The wet season can really be wet but it does not last more than 5 months in total.
There are links to the older New Mexico adobe code with an update to the newest code coming soon on www.quentinwilson.com. I think the old one is more appropriate to your location.
Question: Can you make an adobe plaster type mix to cover an old unpainted cement block wall?
Answer: (Kelly) Yes, adobe does adhere pretty well to a cement block wall. Make sure there is enough clay in it to make it sticky, without causing it to crack too much.
Question: Should I mix anything else with the clay, and what is best to seal it so as it won't fall apart with the many changes of weather like rain, wind, dry heat, sun here in the Las Vegas desert climate we have?
Answer: (Kelly) Ideally you want somewhere between 10% and 30% clay, with the rest sand to keep it from shrinking and cracking too much. Sealing it depends partly on how well protected the wall is from the weather by roof eaves. If it is tucked under sufficiently, the straight adobe soil mix will hold up pretty well. Otherwise, you might want to add some Portland cement (maybe 5-10%) to help stabilize it.