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Rapidobe - cheaper, easier alternative

 
Abe Connally
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Location: Chihuahua Desert
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We've developed a semi-new form of construction that is similar to Oehler's PSP, but a little different. Because wood is hard to come by in our area (and many areas of the world), we decided to go another route.

We use billboard tarps for both the retainer and the vapor barrier. The advantage is that you can also build free-standing walls with this, so it doesn't have to be built into a hill.

The basic design is posts, then stucco mesh, then thick fabric (billboard vinyl). Pack with dirt, and once things are settle in, stucco the outside. For the stucco mesh, we use orchard netting, as it's cheap and available.

We call this system Rapidobe (rapid - adobe).

We made a 35ft by 4ft freestanding wall in 2 days with 3 people. We also built a 35ft by 2.5ft retaining wall in a day with 3 people.

For a freestanding wall, you do 2 lines of posts, and then the billboard tarp forms a "U" shape in between the posts, like a big bag. Fill, tamp, tie off, stucco, and you're done.

Here's some more information with detailed photos:
http://www.velacreations.com/shelter/building-components/walls/item/166-rapidobe-walls.html

We'll be doing a barn later this month using this method, and I expect it to work really well, as the site is dug into a hill, and also has some flat areas.
 
Paul Overton
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VERY cool.

Nice site! I liked the self-cleaning overflow, bright idea! Does it work? I'd expect that gravity would still keep some sediment on the bottom.
 
Abe Connally
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Location: Chihuahua Desert
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the self-cleaning overflow is a common thing in aquaculture systems, and it works well in those. Our tank is still not full, so we don't know if it will work for us. I think it will work, but maybe not get everything. Still, that's a good improvement.
 
Karen Crane
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What if you don't have that billboard vinyl? What else could you use?
If you pack with earth, doesn't it settle after awhile?
Do you wet it as you go to help compact it? You use
use rammed earth ideas?
Will look forward to the barn.
Interested to see how this will hold up in rain and snow.
 
Tom OHern
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Location: Seattle, WA
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How to you keep the posts from being pushed apart over time? With only four foot walls this might not be immediately apparent, but eventually the static forces will cause the posts to collapse. The greater the height of the walls of the greater the roof load is, the faster this will happen.

And as far as Underground housing goes, how would these walls hold back the earth berm? There seems to be very little horizontal resistance build in to these walls. With earthbag building you can build the wall sloped into the earth berm and add curvature to give it horizontal strength. I don't see a good way of doing that with this method and am wondering if you had thought through that aspect?

Otherwise, very cool project and I wuold love to see more pictures!
 
Abe Connally
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Location: Chihuahua Desert
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we tamp the earth as it fills, so it makes it very hard. We don't wet it, though it is moist from being dug up.

Any thick fabric would work, billboard vinyl is what we had on hand, and it's cheap and/or free.

For the posts, they are tied together at the top and bottom to prevent them from spreading. You actually have to tie them just to fill it, as they will spread during fill without something hold them together.

For the retaining wall, there are posts in the ground, then their tops are tied to stakes or the next level of posts. You could easily slop the wall into the hill, if you wanted. A better strategy is to stair step these walls up a slope. The top of one level of posts tie to the bottom of the next level.

You can also use a "dead man", which is a big piece of something at the bottom of the backfill that you tied the top of the posts to.

For more photos, check out our Flickr:
http://www.flickr.com/photos/velacreations/sets/72157628554400001/
http://www.flickr.com/photos/velacreations/sets/72157629337022610/
 
Tom OHern
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Location: Seattle, WA
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So it looks like you used 10 or 12 gauge steel wire, right? I haven't done the force calculations but I don't see how that will be strong enough once the forces really start to push on it, especially once it starts to rust out. If nothing else, it will stretch. On a 30" thick wall if you have 10% stretch you are going to see 3 inches of movement. Your stucco coating will not tolerate that.

I would use either epoxy coated rebar or something like this [url-http://www.marshallcomposite.com/cbar.php]fiber-reinforced polymer bar[/url].

Maybe I'm wrong and your wall will hold up. Time will tell I guess. But I would suggest any wall that is actually load bearing be beefed up quite a bit.
 
R Scott
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Tom OHern wrote:So it looks like you used 10 or 12 gauge steel wire, right? I haven't done the force calculations but I don't see how that will be strong enough once the forces really start to push on it, especially once it starts to rust out. If nothing else, it will stretch. On a 30" thick wall if you have 10% stretch you are going to see 3 inches of movement. Your stucco coating will not tolerate that.

I would use either epoxy coated rebar or something like this [url-http://www.marshallcomposite.com/cbar.php]fiber-reinforced polymer bar[/url].

Maybe I'm wrong and your wall will hold up. Time will tell I guess. But I would suggest any wall that is actually load bearing be beefed up quite a bit.


Once you have packed it, it should behave like rammed earth--which is plenty strong, just not weather-resistant (until you add tarp and stucco). Only stretching will be during construction.

 
Abe Connally
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Location: Chihuahua Desert
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yeah, steel wire and then poly rope at the end to "stitch" the top of the fabric down. These walls are about 8-10" wide at the top, 10% stretch is an inch or less.

The roof weight is transferred to the posts through a metal bond beam.

The wall has been finished for a while, now, and no shifting or movement has been noticed.
 
Tom OHern
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It is not possible to get the compaction to the same level as rammed earth if you are using fabric as the form walls. And even rammed earth requires rebar to deal with possible earthquakes or other environments that do not have extremely low humidity. And rammed earth cannot contain large rocks and has to have a carefully prepared soil mix to provided the needed strength, neither of which are being done here.

Don't get me wrong, I think this is a great idea but I think there just needs to be a realistic view of what the appropriate uses for this sort of building technique is useful for. And i think that with a few changes, the longevity and structural strength of a wall like this can be greatly increased. As it is, depending on the environment, I could easily see it standing for 10 or so years. But with very little money and effort, you could make that 100 years or more.
 
Abe Connally
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Location: Chihuahua Desert
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It is not possible to get the compaction to the same level as rammed earth if you are using fabric as the form walls. And even rammed earth requires rebar to deal with possible earthquakes or other environments that do not have extremely low humidity. And rammed earth cannot contain large rocks and has to have a carefully prepared soil mix to provided the needed strength, neither of which are being done here.

Fabrics can be used as forms for rammed earth, and have been so and tested.

What improvements would you suggest for making it stand for 100 years?
 
Abe Connally
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Location: Chihuahua Desert
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here's some innovative work with fabric forms and rammed earth: http://www.rammed-earth.info/project/60/Fabric-Formwork/
 
William Bronson
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allen lumley
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Abe Connally : Yes please , can we have an update ? - What would you do differently if you were going to do a similar build again ?

William Bronson, Thanks for spotting this again and putting it back into the Que ! - for the crafts ! Big AL
 
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