Today’s post is from Dr. Johnny Anderton of of Eternally Solar / EarthBagBuild. We’ve been discussing various aspects of their building system over the last week or so. Clearly, this is another great earthbag system to study and learn from.
“The design of the bags with the central channel allow for a lot of variation in approach to structural elements in the wall, which can be adapted depending on strength requirements.
We have used unstabilised sand only in the wall in our pilot and other projects, in both tubes and channel. The resultant structures are extremely sound and have been tested to destruction for lateral loading, way surpassing international Agrement requirements. The highly compacted sand (created through the weight of the wall above) together with the plaster skins, forms a dense laminate on either side of the lightweight core just as in a structural insulated panel (SIP). Having said that, in a cold Cape winter, we’ve found that the sand acts as an excellent insulator due to the myriad air pockets. Also has a thermal mass effect.
In seismic areas, I would use columns and horizontal stiffeners. How do you build these? Where the plan specifies a column, you end the rows of bags the specified distance apart (say 300mm). This gap in the wall is where the vertical rebar comes up from the foundation. [Ed.: See Confined Earthbag.] This vertical rebar is tied to horizontal rebar that is cast into concrete in the bag channels every 7 bag layers or so as you build the wall. These horizontal stiffeners can run into the bag wall just a short distance either side of the column, or can run right around the structure, creating a bond beam at all these levels.
Once one has built say 1.5 m of wall, you shutter on both sides of the wall, and pour concrete into the space created by the shuttering and between the wall ends. You therefore end up with a cast column and horizontal beam. These can be created anywhere in the wall, whether in a straight of a wall run or in the corners of the structure. You thereby create a very lightweight reinforced concrete ‘lattice’ integrally in the wall. This is a much more engineered approach than using barbed wire and I believe is much stronger.
It would be a good idea to use structural foam on the inside of the shuttering, so as to separate the column both thermally and structurally from the plaster skins. This means that the stiff skeleton of columns and beams is not directly connected to the flexible element (bags and sand fill) nor to the plaster skins. It is desirable to avoid having elements in the wall of different rigidity in direct contact. And this would allow the mass of the wall to vibrate at a different frequency to the skeleton, absorbing the vibrational energy.
With the appropriate engineering input, I believe that a massively strong but flexible wall can be created, which will withstand significant seismic force. And 2 story buildings or more could be created (We’ve not done anything more than single level thus far.)
Having said that, in our non seismic area, we have used unstabilised sand and no vertical or horizontal stiffeners (until ring beam or lintel height). So the wall to that upper level is purely the bags and sand, no barbed wire, steel, concrete or any other material. We don’t even used mesh in the plaster. This is how our test wall was built. Easy to build, nothing to corrode, and plenty strong. The corrosion issue concerns me, as there is always an element of residual moisture in earth walls, and any metal is bound to corrode eventually.”
Owen, can you comment about Basalt rebar’s use and corrosion. I saw some samples at eandhweek.org at SMU and was impressed with it.
One of the things we used on our Ubuntu-Blox house was bale wrap. We used Patti Stouter and her clay formulas for the plaster. The big issue was the adhering to the plastic. We started off with hanging the bale wrap over the blocks each layer.
Patti says we don’t need it. But after looking at the house after it has been transported a total of three hundred miles at speeds up to seventy miles per hour I believe it is a good addition to the design.
We lost about a quarter of the plaster due to the move. Part of this was to the vibration of rough roads I’m sure. Keep in mind the house was secured to the trailer only by it’s foundation. We trusted the wall construction to take care of itself, even at speed. Then there was the speed of course.
I found the bale wrap engaged the plaster very well. Well enough in fact that I’m going to recommend we individually wrap each block with bale wrap before installing it.
Bale wrap is a nylon/propylene fabric used to secure round bales of hay and straw. These bales weigh up to fifteen hundred pounds. It cost less than $300.00 for a roll four feet wide and five thousand feet long.
Look for recycled mesh bags, the kind used for onions, oranges, etc. and wrap those around your blocks. That way you’d have 100% recycled plastic block. Maybe you could find a produce supplier who would donate used bags.
Basalt rebar is new to me. I’m still reading about it. It seems comparable to steel rebar and superior in some ways (doesn’t rust or conduct electricity). I’ll have a post coming up very soon on basalt mesh, fibers and roving (twine).
I hope people are taking notes or copying this info to a folder for later use. This info is pure gold. Imagine building a house that surpasses engineering requirements/tests using just sand and bags (and a tiny amount of concrete and rebar). You couldn’t do that with typical bags unless the sand was stabilized somehow.
yes, this inf is extremely useful!
I wonder how long the plaster will last without metal mesh, though. I’ve seen adobe and block buildings with non-mesh stucco, and the plaster doesn’t last beyond a few years. Without something to grip and/or reinforce the skin, I would worry about its durability.
Could the non-compacted, no barbed wire sand system work in a bermed or buried structure? There will be increased lateral loads on the walls, but it might still work.
This is typical. It seems most earthbag houses don’t have mesh. While mesh will add some strength, it’s not required in most cases. Mesh is strongly advised in seismic areas.
really? I had thought that most used stucco mesh. What sort of plasters do most use? If it is earth based, then mesh might not be necessary, but if it is cement based, I wouldn’t trust it. I’ve seen too many failed stuccos….
There hasn’t been any formal survey of what people are using, so what I’m saying is just an educated guess. Most people are using cement plaster without mesh on the exterior. Lime and earthen plaster are also very popular. Earthen plaster needs wide roof overhangs.
that’s interesting. In almost all of the online documents and/or earthbag books, they describe a mesh reinforced stucco…
That’s the typical way on most conventional houses and so books and articles will naturally recommend the normal way, but we hear of lots of people not using mesh. Kelly and I don’t use mesh.
wow, that is good to hear. are you using concrete-based plaster (I know Kelly likes papercrete)?
Any examples of long term durability without mesh (5-10 years)?
Kelly is no longer a big fan of papercrete. His house turned out fine, but there have been too many mold problems.
There’s no centralized database of houses, how they were built, etc. You might be able to track down some homeowners and learn about their experiences.
hmmm, I wonder if we should make a central DB of earthbag builders, like a community to share info?
Sounds good. Tell me more.