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Questions: Use scoria (cinder rock, lava rock, or pumice) for earthbag building that is not a dome?  RSS feed

 
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I have researched earthbag building using scoria, but have only come across those buildings that are domes.  We plan to build a 12' diameter round building that will be a kitchen/dining area.  Originally we were going to build it completely separate from our tiny house that is on skid foundation.  We have since decided to join to our home with a passage.  We are in North Central Arizona near Valle (halfway between Williams and the Grand Canyon) and have mildly cold winters.  December seems to be the coldest month with January and February also cold, but not as cold.  The lowest temperature last year was 6 degrees, but most nights are in teens and day temps in low to upper 30s, usually sunny.  Here are my questions:

1. Will scoria material be strong enough in the walls?  We will have a tin lean-to type roof on our round building.  The cinder rock is 3/8", give or take, and packs well.  The walls will be 7' high.  We plan to use 2 strands of barbed wire in each course and use 18 x 30 bags. 

2.  Insulating factor and winter heating?  I have read that in this general area that scoria earthbag buildings may be zero energy.  We will have passive solar coming in the south.  The passive solar heats our little house on sunny days in the winter, having only to start the wood stove late afternoon, before bed, and sometimes very early morning, or at least when we awaken.  We have a wood stove in our tiny house that will have some heat flow into the round kitchen via the passageway, which will be pretty much directly behind the wood stove.  We are thinking we might want a small wood stove in the kitchen just to knock out the chill for morning coffee and breakfast, but not sure if we will need it.  We do have a medium size Buddy Heater to use with propane to knock out the chill, but we have about 3 years' worth of wood so see no sense in buying propane.  We do have another tiny wood stove, but will need to purchase the flue pipe, double or triple wall pipe, chimney cap, etc. if we install a wood stove.  I am thinking that we should go ahead and plan for a flue, and block it off if we don't need it after all. 

3.  If you have built with scoria earthbags, did you have any challenges and/or positive comments you would share with me?

4.  Concern about mice?  I have read on the Mud Mountain website that if you use rock instead of earth in the earthbags, mice may eat through the plaster and into the bags when they can't with true earthbags using soil.

Thanks in advance for providing information, answering my questions, and/or general comments.

By the way, our soil here has been confirmed as clay only; no sand, and we would go with earthbags filled with clay and sand, having to haul in the sand, but the soil is also very rocky and hard to dig, and scoria is relatively cheap in our area.  That reason, and the reason of dealing with bags with half the weight of earth filled bags, we decided on the scoria, and also the insulating factor.
 
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1. Yes, it'll be plenty strong enough, just lay it tight, plumb, running bond, leave some wall between openings or carry with decent framing if you slam openings together, etc. That's a tiny roof on thick round walls. I much prefer 3/4" aggregate for serious structural scoria bag. I use 1/4" scoria for lightweight concretes. Try to find a bigger size if you can. If not, you'll be fine at your size and roof type. And make sure they screen the fines out!
I suggest Considering making it bigger than 12' diameter. If you are gonna go through the steps of foundation, bag, plaster, roof, plumbing, wiring, doors, etc, a few more foot diameter ain't much more work and it's much more enjoyable. I know you're going tiny, but my original 25' interior diameter scoria bag dome just keeps getting additions on all sides...

2. R value--i think that's a joke of a rating for Owen Corning to validate their fiberglass in a perfect lab conditions. But wind doesn't blow through 16" of scoria bag, nor does humidity degrade it's thermal performance. Temperature doesn't change it's performance like foams. And it is hard to improperly insulate the scoria bags.
I think scoria bag performs comparably with strawbale laid on edge, although the scoria has a lower R, it has a mass enhanced insulative value. Yes ideal to separate and outsulate in exterior wall/roof systems, but it works great (kinda like ICF works great). Not looking to argue this with anyone who hasn't lived in one, they never get it... I'm in a colder climate and proud of it's thermal performance.
Your build is small, it'll take nothing to heat. Some passive solar and a small stove of sorts. I prefer wood stove and operable windows. Small cheap round buildings is where scoria bags shine in my opinion.

3. Challenges.. 25' interior diameter dome is rather challenging. The other 4 scoria bag projects were straight forward. Youre round, but if others are reading, corners on straight walls can experience slump if not planned for. Don't get delivery via belly dump. I love plastering, I do some stucco side jobs I enjoy it so much. Most prefer to drywall just because.. Just know that. Have fun. I really like scoria bags (and strawbale, and brick/blocks and ferrocement and rammed earth with a tractor). Earthbags are more work, and tires or hand cob are much more work. Scoria bags hit the sweet spot with cost, speed, ease, insulation--if locally available. The only other suggestion is rammed earth with a tractor and straight walls since you are building so small with a shed roof, if you're find a pocket of right dirt.
4. Haven't noticed any mice in walls or bags. Just detail it well.
 
M. A. Carey
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I much prefer 3/4" aggregate for serious structural scoria bag.



Hello, Christopher.  Thank you so much for your response as it is very helpful to me and gives me peace about our decision to go with scoria versus soil earthbags.
 
We had purchased 1" +/- cinder rock previously, for another project (not earthbag) and ended up with a lot of large cinder rock, like 1-1/2 to 2" in the mix, but also some 1/2 to 3/4", and I am afraid to go that same size for our earthbags, thinking there will be a lot of big rock in to have to pick out.  The only offering is 1" +/- or 3/8"+/-.  I wish they had something in between, like 3/4" but they do not.  We will have to screen the 3/8" because there are a lot of fines in there. 

Do you think we could mix the 3//8" with up to 1" and be okay, or just screen the small fines out of the 3/8".  I thought the 1" would be good enough, but I had read on another website that anything over 1/2" doesn't pack well when tamped.   Either way, with 3/8" we will have to screen and with 1" will have to pick out the bigger rock.  I am not sure which would be more to deal with.

I appreciate your feedback.  The 12' inner diameter will be okay since it will mostly be used for food storage, cooking, and eating.  There are only the two of us.  We live completely off grid, using solar panels for electric, haul our own water from 4 miles away, and our plumbing is basically a DC pump inside our tiny house that will be transferred to the kitchen when completed.  We use compost toilet, and have a solar shower house that in the late fall, early spring, and winter we heat water and add to the solar water tank. 

One of these days, I would like to build a larger earthbag building, but this is a first time project for us to learn from and not become overwhelmed during the process.
 
pollinator
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Location: Cincinnati, Ohio,Price Hill 45205
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I have nothing to add, having no exporience, but your thread has inspired some fun research.
That being said,i couldn't find out what the downside of fines in the mix would be.
I would expect fines to be good and assist in the packing process.
Concrete with a variety of sized aggregate is stronger, and lumestone crusher run is said to pack up hard enough to be a road surface.
Does the inclusion of fines degrade the insulative properties by filling in the air voids?
 
Christopher Steen
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M.A.: go for the inch minus and don't pick out the inch. Try grabbing a few buckets of that inch,x9 fill a bag, sew it closed with some wire, tamp it solid and cut the bag off. You'll see that it's all locked into place. I've removed enough to know the larger stuff is what you want.
You could always look for a screen at scrap yards, landscape yards, etc. Pretty handy for plaster too. But best to get it already screened. You could ask your supplier of they have a 3/4 screen, but I get a lot of inch in my 3/4.

William: you're correct, the fines block out the insulating voids.
 
Posts: 45
Location: Colorado Springs, CO zone 5A / Canon City, CO zone 5B
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Here are links to two posts about our 14' (inner diameter) scoria bag tank house. http://www.naturalbuildingblog.com/thermal-performance-data-earthbag-dome/#more-11686    ; https://www.facebook.com/profile.php?id=100006725657912&sk=photos&collection_token=100006725657912%3A2305272732%3A69&set=a.1569408199960020.1073741827.100006725657912&type=1&l=9dd7088781

The bags are great for walls as long as you build plumb (in your case). They are not as solid as earthbags and can feel a bit wiggly as the height increases.

This is a video by a guy who made a rectangular casita and used strapping to compress the walls.  https://www.youtube.com/watch?v=YJS8Kozufl4 ; We used baling twine ala Kelly Hart, and it really helped. The only down side of the twine is that there is no way to tighten it up later on, and as you add rows of bags, the lower ones compress a bit. The strapping might solve that issue if you keep the tightening points out where you can get to them.

Because we did not get an exterior coating on before winter, we tarped the building, and mice chewed all over the place to find shelter. We used several rolls of Gorilla tape the following spring to keep the fill from falling out. And we still had lots of UV degradation because we took no intermediate steps to protect the bags during the course of autumn bagging (8 weeks in Colorado).

I thought I had a more comprehensive post here, but I guess I was dreaming. PM me if I can answer any more questions for you. We really love our building, especially the thermal evenness provided by the scoria and the concrete. I would build again with scoria in a heartbeat.
 
M. A. Carey
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Because we did not get an exterior coating on before winter, we tarped the building, and mice chewed all over the place to find shelter.



T. Phillips:
After you completed the tank house, did you ever have problems with mice? 

Once we plaster the exterior, we are also going to plaster in some flat rocks of all sizes the first 18" to 24" of bottom and make sure the plaster covers the  edges  of the rock, hoping that extra material will discourage rodents.  We also will have more rock (large flat pieces and then cinder rock piled up against the bottom 10" or so grading outward from the building.  If we were using actual soil bags instead of scoria bags, we wouldn't worry so much about rodents, but I would sure hate that they get in and chew into bags, causing the rock to fall out between plaster and what would be left of the wall.  I would prefer to use soil earthbags, but they would be too heavy for us and also we get cold winters and want the insulating value of the scoria.

We plan on using strapping to keep the walls tight.  We purchased Kelly Hart's book, which has given a wealth of information, as well as Permies.com and several other websites. 

I deleted my FB account 6 months ago, so I am not able to go into yours to look at your info.  
 
Posts: 587
Location: Thunder Bay, Ontario, Canada
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Just a heads up...

I grew up in a volcanic field and as a youth, I spent a lot of hours moving scoria for drainage etc.

The stuff is a nightmare to shovel unless it's in teeny weeny pieces.

Just like Paul recommends pounding tires for an hour with a sledge hammer before embarking on an earth ship, I recommend you spend an hour filling earth bags with scoria before embarking on a full scale project.
 
T Phillips
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Location: Colorado Springs, CO zone 5A / Canon City, CO zone 5B
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We have had zero problems with mice since the final covering was applied. We are enormously pleased with the thermal performance of the building and it's ability to weather our local micro-burst winds. (The insurance company gave us enough money to pay for a well after the horse shed in that spot blew down. We knew that for that location we wanted a structure with an integrated roof.)

The scoria we ordered was 3/4" and it was like shoveling Fruity Pebbles after the gravel for the first two rows. The 15" x 25" bags weighed about 25-30 lbs. each with 6  #10 can scoops of scoria inside and stapled shut. They finished at about 12" wide. (Some bags were larger and some smaller.) I was a 57 yo couch potato who became the primary builder. My lower back hurt for 2 weeks, then was fine. I lost 10 lbs. in two months despite eating like a horse, working 4-6 hours/day. Most satisfying work I've ever done.

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Mouse damage
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Note all the gorilla tape
 
M. A. Carey
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Nick Kitchener wrote:Just a heads up...

I grew up in a volcanic field and as a youth, I spent a lot of hours moving scoria for drainage etc.

The stuff is a nightmare to shovel unless it's in teeny weeny pieces.

Just like Paul recommends pounding tires for an hour with a sledge hammer before embarking on an earth ship, I recommend you spend an hour filling earth bags with scoria before embarking on a full scale project.



Hi Nick.  Thanks for the heads up.  However, we have shoveled and moved cinder rock around our place, off and on, for about 1-1/2 years.  We have up to 1-1/2" rock and now have a start on some 3/8" +/- rock, and have worked with both.  We have yet to fill bags because we are waiting for warmer weather for our project.  I would prefer to find some 1/2 to 3/4", but it is not available in our area cinder rock quarries, and they don't screen any of it.  So we have shoveled different sizes, but haven't experienced dumping in bags.  We have been forewarned now, regarding filling the bags with scoria. 
 
M. A. Carey
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T Phillips wrote:We have had zero problems with mice since the final covering was applied. We are enormously pleased with the thermal performance of the building and it's ability to weather our local micro-burst winds. (The insurance company gave us enough money to pay for a well after the horse shed in that spot blew down. We knew that for that location we wanted a structure with an integrated roof.)

The scoria we ordered was 3/4" and it was like shoveling Fruity Pebbles after the gravel for the first two rows. The 15" x 25" bags weighed about 25-30 lbs. each with 6  #10 can scoops of scoria inside and stapled shut. They finished at about 12" wide. (Some bags were larger and some smaller.) I was a 57 yo couch potato who became the primary builder. My lower back hurt for 2 weeks, then was fine. I lost 10 lbs. in two months despite eating like a horse, working 4-6 hours/day. Most satisfying work I've ever done.



Thanks so much for the pictures and the information, T Phillips.  We know it will be physical work, but are still looking forward to it.  My husband loves to keep busy and isn't afraid of physical labor.  Me, well, uh, let's just say, I will have to keep up my part.  Because of me is the reason we chose scoria instead of the soil eathbags, as I would be worn out after a couple hours doing the 80# plus bags, even with his help.  I am 60 (had back fusion surgery 6 months ago and healing great) and my husband is 64, but works like he is a 24 year old. 
 
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