Hello Nathanael,
Thank you for adding a link to your post. I had actually looked up the same map, so I could refamiliarize myself with your location.
Adobe probably isn't the dominant form of building with earth alone in the entire region of Chad and "cobb modalities" and systems similar to "Bajareque" (I have forgotten the regional term for this style) is probably as common if not more so for some areas.
River banks and other water sources can be a great source for clay bodies, but are not the primary source regionally through most cultures that build with earth. It is just the dirt dug and processed on a building location that is utilized most commonly.
Animal manures primary application is not for the "mucilaginous" effect than can occur, but rather the consistent fiber matrix contained in most "Ruminant" waste. Any enzymatic reactions that also takes place and the mucilage contained therein, is a positive byproduct as well, and does aid in giving a more plasticine characteristic to the clay medium. Rice soups, and other grain starch additives/binders sometimes play a role as well in the many recipes, as does cacti and seaweeds. Fermentation reactions, as far as I know, have little to do with these reactions in general, but do perhaps in other areas play a more vital role, such as "aliz" and other clay based finishes, and outer renders.
...The adobe house is built by layering the mud one layer at a time...
The description above was a bit confusing as it describes the "layering effect" of "cobbing" method, and can also be found in some "Bajareque" modalities.
I
should clarify...technically...that "adobe" styles around the globe, are "brick or block" formation modality done by either forming these shapes entirely by hand, but more commonly in molds or forms. They are then placed in the sun to dry until ready to be employed within the construction matrix of a building or other structure's wall or vaulted/corbeled roof diaphragm.
I would also point out that it is a common "Eurocentric" view that most of these methods (i.e. cobb or adobe) are mainly "post European invasion" of the regions. Africa has and had a well formed stone, timber, earth and textile based architecture history for millenia, and long before Europe ever did. So I would suggest...for historical accuracy alone...that we understand the most of the methods (and the forms most germane to the region) are African in orgin, and not European.
This works to greatest effect on a free-standing wall surrounding a yard or a city because termites have little incentive to tunnel through this structure. But when used to build a house one needs a roof, and that's where it gets complicate. Whether the roof is straw or adobe the wooden support structure is a termite attraction.
I am a bit confused by much of this post
thread at this point...
If we are to explore viable methods to build in this region, then I can be of assistance in helping interpret the many outstanding vernacular methods to build structures, and still strongly suggest finding an indigenous builder to gain deeper knowledge. The above quote is "subjective" at best and I am not sure how I can address it, as clay, straw and timber structure...when facilitated properly...can be built anywhere in this region to good effect. If that is to be the goal, I would love to be of assistance. Rammed earth methods could also be considered, perhaps with a vaulted ceiling of adobe block. This will require more skill and lime binders as well. I am not a fan of "earthbag" (EB) architecture in comparison to RE but it has a place in the list for consideration, and does (CEB) if available and well made. Fossorial building forms as well from other similar biomes may well have application in
dryer and well drained building sites.
If the potential building location is near a river or other body of water that is wonderful for a number of reasons, but is not, as stated before, the primary source for clay bodies in most styles of this architecture. It is a convenient one if available.
As for the "roof issue" that could be a design flaw from a misapplied vernacular system or just part of the annual maintenance process for a given style. Without specifics I can not speak to the modality or its given durability. I can speak to examples in regions of the Iberian and South West Indigenous building styles here in north America, that have annual reapplication needs to both roof and walls of clay aliz and other rendering materials as part of the "maintenance process" and many of these structures are in good standing century after century if properly maintained. Any structure, natural or modern, will require a degree of service on a regular basis to stay in good order.
Transient "hut or shanty" architecture may well indeed have a shorter lifespan than more robust forms but also are much easier to build as well. I will share that it is a choice of which style one cares to follow...robust or transient...as there are structures of earth through this and many regions of Africa that are multigenerational in nature, just as we have Kiva and Adobe structure here and in South and Central America (with similar climates) that are well over 1000 years old.
I do understand the undeniable and dominable effect that some regions face from termites and have seen this in those regions myself. It does not preclude what I have share thus far, and we need to get more into details of a chosen system before it would be prudent to move into "holistic" methods of mitigating termite issues. I can say this is done by proper material selection, methods and even some "treatments" that can be an ongoing need, but does not have to involve harsh chemicals or moder toxins. From the specific regions challenge, it looks like a "termite resistant" wood species (which do exist) will have to be found for the roof and wall frame work, and treatment modalities are going to be the key to more enduring styles of building. I would stress again looking to the more "enduring vernacular forms there" and looking to artisan that still build them for advice. I am more than willing to help with interpretation and specifics were able.
Regards,
j