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Earthbag-Scoria vs. earth in Hot Nicaragua?  RSS feed

 
joey melroy
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Hi all this has a couple parts to it. I am going to build in Nicaragua where it is Hot year round. Bone dry six months and rainy six months. I think Scoria (porous volcanic rubble) is available and cheap here. Clay and sand are also readily available.

I have seen sand clay mix recommended in hot climates and also pure Scoria bags for good insulation in cold climates.
Could Pure Scoria work in a hot Climate as well?
For walls on a home is it practical to use Scoria as an aggregate mixed with a clay sand mixture to help lighten the bags?
This will be less insulated when the pores are filled with sand and clay but could this still have practical value?

Another question is are Earthbags practical for a wall at the perimeter of the property?
This will obviously be exposed to the elements with no roof so maybe sand/clay mix is not practical.
Could I use Scoria bags for a property perimeter wall and use a cement stucco in this case?

Any advice would be greatly appreciated!!



 
Gregory Pappas
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joey melroy wrote:Hi all this has a couple parts to it. I am going to build in Nicaragua where it is Hot year round. Bone dry six months and rainy six months. I think Scoria (porous volcanic rubble) is available and cheap here. Clay and sand are also readily available.

I have seen sand clay mix recommended in hot climates and also pure Scoria bags for good insulation in cold climates.
Could Pure Scoria work in a hot Climate as well?


Very good question. I have built an earth dome in Honduras and we used a sand/lime/cement mix for our outer coating/plaster. We used cement because we didn't have time/money to put a roof on it, and the whole project was to try out the wall building technique, not much more than that. I can say that on a very hot day, stepping into the dome felt like stepping into a room 10-15 degrees cooler. And at that point we hadn't put any windows or a door on the structure. I'm going to be in Honduras again next month to build a 2 bedroom home using earthbags and was pondering the same thing. I think it'll help regulate the temperature of the home, regardless of whether it's in a hot or cold climate.


For walls on a home is it practical to use Scoria as an aggregate mixed with a clay sand mixture to help lighten the bags?
This will be less insulated when the pores are filled with sand and clay but could this still have practical value?


I wouldn't recommend using scoria for wall building. You want the clay/sand to bond to more or less create giant adobe bricks. For the same reason, you need to thoroughly sift the soil before filling the bags for the wall sections. Again, it's my opinion, but I can't see the sand/clay ever being able to create as good a bond with scoria added to create a well stabilized bag. You may want to make a few test bags, pound them out and let them sit to dry for a few weeks. Then run some tests to see how strong/stable they are.

Another question is are Earthbags practical for a wall at the perimeter of the property?
This will obviously be exposed to the elements with no roof so maybe sand/clay mix is not practical.
Could I use Scoria bags for a property perimeter wall and use a cement stucco in this case?

Any advice would be greatly appreciated!!


As far as walls for the perimeters, I've seen many in books. Usually the photos are of homes in Arizona and other dry climates that don't get much rainfall. What they're filled with I don't know. It would make more sense to fill those bags with scoria and use a cement stucco to cover the bags, as water absorption/retention (due to the cement) wouldn't be an issue. Also, the scoria (nor the poly bags) won't be adversely affected by the moisture. What you absolutely must pay attention to is the poly bag exposure to the sun. When I first started my project in Honduras, we used a giant blue plastic tarp to cover the foundation gravel bags. We used blocks to hold the tarp down but one weekday (we were only working on the project on the weekends) the tarp was blown around a little and just a small corner of a bag was exposed. Within the week span of being exposed to the sun, the poly section literally turned to dust and the gravel was spilling out all over. (we forgot to double bag the foundation). If you use unstabilized scoria, you could run into the same problem, especially with the intense sun in Central America. Like I said earlier, I'll be in Honduras next month building a home, which is on the same property as my test dome. I plan to cut open large sections of the cement/lime/sand plaster to see what kind of moisture was absorbed and retained. I'll be testing sections of the bags as well to see for myself whether or not cement is the enemy of earthbags as I've found in my research.

When do you plan to start your project? What part of Nicaragua? Would love to hear more about it.
 
Christopher Steen
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Scoria is insulative. It is thermally valuable in climates where you want your interior temperatures moderated from exterior temperatures. Thermally it makes the most sense to have insulative exterior walls and mass interior walls, with the exception of those areas which are hot during the day and cool off considerably at night, and have decent cold season solar gain--those areas comfortably allow straight mass exterior walls.
Nonetheless, thick mass walls work wonders in hot climates especially if shaded with deep roof eaves (which are also good for natural foundations/walls in rainy environments). EB walls are substantial.
Yes pure Scoria bags are lighter and quicker. Offset that with costs--material and labor. If only a few workers or have other jobs then Scoriabag may make more sense. If this is a big group effort, then maybe show them pure earthbags.
As for mixing Scoria aggregate and clay/sand: don't think you Get the best of both worlds, insulation and mass simultaneously. That's the WRONG REASON to combine. Thermally, It'll just perform as mass. It will lighten the load a bit though and labor should increase as a result.
Also I disagree with the previous comment about it not binding. It'll bind with appropriate clay content as well as the larger aggregates mechanically locking in together. So maybe determine your clay content. If it is high, either cut with sand or Scoria or gravel. Start your tests from 3 aggregate : 2 sand : 1 clay. Which for a high clay content dirt could mean 1 Scoria: 1 high clay content clay-sand dirt. Why did I say gravel? Because we are not talking about some tensile strength here, bag fill is not the tensile stuff of ferrocement or fibers or steel cable. We are talking about compressive strength mass wall construction. It is not monolithic, it is a bunch of tamped bags. The importance here just as much plaster work, I believe good distribution of aggregate size makes sense. All different sized aggregates tamped and locked into place by both clay binder and aggregate distribution. Yes its overkill to state this and to even apply over a regular screened earthen fill but you asked if "there was any practical value to combine Scoria (lightweight larger than sand aggregates) to clay and sand even though you don't receive pure Scoria insulation values". My tests showed that bags with larger and more diverse aggregate performed better--less water usage, quicker dry/hardening time, higher compressive strength, more stable without the bag (and all sands and clays and gravels and scoria have different properties and respond differently--so test each soil). A few times I have seen this combined for the WRONG REASON (thermal performance) in my cold climate, so I must spell this out here for future googlers.
I believe larger aggregates in earthbag fill makes better earthbags; better Scoria aggregate size distribution makes better scoriabags; and logistically (labor or cutting down clay content) the inclusion of Scoria could make the jobsite more efficient. Depends upon mixing methods, material and labor cost, clay content. Doubtful you'd notice any difference in thermal performance from earthbag and earth-Scoria bag mixed at previously stated ratios although it does lighten the bag somewhat.
 
joey melroy
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Christopher, thank you so much for your response and valuable input. It is nice to hear from somebody that has tried and proven a few methods here as I know nothing yet It sounds like the scoria is hugely less labor intensive in bag preparation but a little more labor to secure the lighter bags when making walls. I may try this for a little storage house first and see if it gives that cool fooling inside on a hot day. It is good to hear that mixing the scoria with sand and clay wont really sacrifice strength and insulation but could make a lighter bag and could ease the labor load of placing 100lb bags. Maybe I will try this for the walls of a bungalow to test it out. It sounds like many things are possible! Thanks again for the info!
 
Gregory Pappas
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Christopher Steen wrote:Scoria is insulative. It is thermally valuable in climates where you want your interior temperatures moderated from exterior temperatures. Thermally it makes the most sense to have insulative exterior walls and mass interior walls, with the exception of those areas which are hot during the day and cool off considerably at night, and have decent cold season solar gain--those areas comfortably allow straight mass exterior walls.
Nonetheless, thick mass walls work wonders in hot climates especially if shaded with deep roof eaves (which are also good for natural foundations/walls in rainy environments). EB walls are substantial.
Yes pure Scoria bags are lighter and quicker. Offset that with costs--material and labor. If only a few workers or have other jobs then Scoriabag may make more sense. If this is a big group effort, then maybe show them pure earthbags.
As for mixing Scoria aggregate and clay/sand: don't think you Get the best of both worlds, insulation and mass simultaneously. That's the WRONG REASON to combine. Thermally, It'll just perform as mass. It will lighten the load a bit though and labor should increase as a result.
Also I disagree with the previous comment about it not binding. It'll bind with appropriate clay content as well as the larger aggregates mechanically locking in together. So maybe determine your clay content. If it is high, either cut with sand or Scoria or gravel. Start your tests from 3 aggregate : 2 sand : 1 clay. Which for a high clay content dirt could mean 1 Scoria: 1 high clay content clay-sand dirt. Why did I say gravel? Because we are not talking about some tensile strength here, bag fill is not the tensile stuff of ferrocement or fibers or steel cable. We are talking about compressive strength mass wall construction. It is not monolithic, it is a bunch of tamped bags. The importance here just as much plaster work, I believe good distribution of aggregate size makes sense. All different sized aggregates tamped and locked into place by both clay binder and aggregate distribution. Yes its overkill to state this and to even apply over a regular screened earthen fill but you asked if "there was any practical value to combine Scoria (lightweight larger than sand aggregates) to clay and sand even though you don't receive pure Scoria insulation values". My tests showed that bags with larger and more diverse aggregate performed better--less water usage, quicker dry/hardening time, higher compressive strength, more stable without the bag (and all sands and clays and gravels and scoria have different properties and respond differently--so test each soil). A few times I have seen this combined for the WRONG REASON (thermal performance) in my cold climate, so I must spell this out here for future googlers.
I believe larger aggregates in earthbag fill makes better earthbags; better Scoria aggregate size distribution makes better scoriabags; and logistically (labor or cutting down clay content) the inclusion of Scoria could make the jobsite more efficient. Depends upon mixing methods, material and labor cost, clay content. Doubtful you'd notice any difference in thermal performance from earthbag and earth-Scoria bag mixed at previously stated ratios although it does lighten the bag somewhat.


How do partial scoria filled bags react in walls if needed to be drilled or opened for any reason such as plumbing, or piping through?
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