Closing an Earthbag: In Reply to Questions

We’ve had a few questions as to how we closed our sandbags after filling them with scoria, so here are a few photos we hope will help.

We generally used two 2-1/2″ nails to close the bags, folding the ends like an envelope.

A note about the nails, at first we used Dipped Galvanized, which was a pain because the majority of nails in a 5 pound box didn’t have sharp pointed tips, some were like duck bills which made pushing them through the bags a nightmare. We ended up using “Bright Common” box nails, which seemed like a dream afterward. And stay away from “Big Box” stores when buying your nails. Mom & Pop hardware stores often sell them in bulk for a lot less.

Sometimes we used three 2-1/2″ nails if the folds didn’t seem like they were going to stay closed, or if we added a bit more scoria than the previous bags. Even though the 3/4″ scoria was mostly the same size, there were times when digging through the pile we came across larger and smaller pieces, so we had to compensate. The average amount of scoria per bag was about 7 gallons. (Your amount may differ).

We folded in the bottom of the bags before we filled them. (You don’t have to turn the bag inside out to do it). You place your right hand inside the bottom of the bag to catch the corner as your left thumb pushes it in. Try it a few times… you’ll get the hang of it.

Before we actually started building, we tested out a few bags by filling them with scoria, and then built a form that would make the bags uniform in size.

The form was made out of scrap 1″ x 6″ with the back and sides as one piece. The front panel was removable and held into place using two C-clamps. Once we filled the bag and closed it with nails, we removed the C-clamps and dropped the front panel down, which allowed the filled bag to lay flat… and this made it easier to pick up. The bags weighed an average of 40-50 lb each.

Since we didn’t have scaffolding, we filled the bags on the back bed of the truck as we got higher in the building process. We still had to heave the bags into place, which was tricky when you have a height of 17′, but it’s doable… and you’ll have a great set of biceps after you’re finished.

Here was the first bagging station we used for the first 40 cubic yards of scoria. We actually sifted the scoria before we filled the bags, because the scoria we had delivered had a lot of dust in it, and we were concerned that this would inhibit the insulation property. But we discovered that this took too much time if we were going to finish before the first snow. Insulation is only good if the building is closed… so after the second scoria delivery, we just filled the bags directly. We ended up filling a lot more bags faster by doing it this way.

Also notice our “Frankentamper” in the photo.  We used a yogurt container for the cement mold which fit inside the form beautifully. This one tamper (along with a lot of Gorilla Tape) lasted through 2000 bags. (We plan on donating it to the Smithsonian.)

If we were going to do it again, we would have made three or four tampers beforehand since making another one would have broke our rhythm, and at the end of the day we could barely make dinner let alone a new tamper.

Note: We found out  just in the nick of time before ordering that here in Montana scoria is a non-porous stone completely different from lava rock. So when you order your scoria, make sure it is what you think it is. Here in Montana, scoria and lava rock are two different beasts.


7 thoughts on “Closing an Earthbag: In Reply to Questions

  1. That’s a handsome bag filler. I wish scoria would work in the desert but the denser soil mix will keep the interior cooler. I’m going to rig a block and tackle to get the buckets of soil up to the bags on the higher courses. Tossing coffee cans of soil was quite the mess on most projects I’ve worked on.

  2. Wow, there’s so much helpful information here! Thanks for clarifying about how the nails were used – I definitely had the wrong idea. Also, the distinction between scoria and lava rock – crucial info.

  3. I was wondering if you filled your bags with only scoria? I have heard that you need to do that instead of using earth in cold climates. We are going to be building in Canada, and I want to make sure that I have a clear understanding of the process. So you filled the bags with scoria, and no dirt, and pounded them flat like you would if you had filled them with dirt, right? About how much a yard or ton did you pay for the scoria? Is it easy to work with? Should it be fine or chunky? I have not seen scoria before, and I don’t know what it is. Every time I see a photo on any blog, the scoria looks red, and fine. If you could clear up my confusion, that would be lovely. 🙂

    • Hi LaZell, yes we only used lava rock (scoria) when we filled our bags. No dirt what-so-ever. The 3/4″ lava rock (about 90 cubic yards) cost us about $5,000.00 USD. We did tamp them as you would with dirt filled bags, but you have to experiment with the amount of lava rock per bag and tamp it to find the right balance of firmness. 3/4″ lava rock is… chunky, not fine. I have an image of lava rock compared to a penny I can email to you if you’d like. It was easy to work with, and since we live in Montana, (and survived our first winter in the dome)… although not completed in terms of final plastering inside and out… the insulation properties are great. We were never uncomfortable in the dome even when the temps dropped to -20F outside for a week or so. Hope this helps. Thanks for visiting.

  4. hi there, could you tell me what the average temperatures in Montana are and do you suggest working on a project at a particular time of year. I’m asking this as I am in NZ and was wondering whether this would be suitable for me to work with here.
    Thanks for the great information, as I too was wondering whether you added anything else to the bags.

    • Hi Justine,

      When we started building the dome in July the average temperature during the day was in the 80-90’s, and dropped down into the 50’s in the evening.

      We finished building the first week of October, and started applying the exterior mud for 10 days straight before the temperature dropped to freezing, and we didn’t complete all three domes before the first snow fell a few days after we completed the second dome. We covered the third dome for the winter with a tarp. When it warms up again, we’ll complete the third dome. During the winter, the temperature dropped into the -20’s for weeks at a time.

      So unless you get snow, and depending on your exterior finish requirements for drying, pick the best weather to build. We knew we only had a window of three months to finish, which was a great motivator for us. Thanks for visiting.

  5. Wow, you guys didn’t start til July and were done by October? That’s very encouraging, as my building start date keeps getting moved back. It’s looking like I won’t be starting until the beginning of June now, and my goal is to be done by the middle of October or so when cold weather hits.

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