Covering Earthbag Walls: 4 DIY Options & Tips

Adobe Mud/Cob/Soil/Dirt

I used the same soil for filling the earthbags and covering the exterior and interior walls. It doesn’t get cheaper than that. I did not even use any straw in the mixture, but I did add two cups of tapioca powder to approximately five five-gallon buckets of dirt.

Covering earthbag walls is easy with these materials: soil, water, and tapioca as a binder, stucco, concrete, and a lime/sand mixture. Mix the materials and apply in thin coats starting at the bottom of the wall and work up. The first coat is to fill in the area between the earthbags to make the wall more flat.

The locals here in Thailand use locally grown tapioca powder as an adhesive. It is very viscous and it reminds me of working with polymers in the water treatment industry.

Covering Earthbag Walls
Air working on the interior while I do the same on the exterior in the heat

Steps For Making Natural Glue For Adobe Mud

  1. Purchase 2 – 5 1-kg bags of tapioca powder. I used two bags of tapioca on the last two coats after I decided I needed it after I did the first coat. My earthbag house is 16” round and 6′ high so larger wall areas will need more.
  2. Use a large soil mixing tub, or wheelbarrow, or just use level land. Add the dirt.
  3. Use a spade shovel, hoe, or your feet and mix in water to a consistency that is thick and sticks to your hand when you hold your hand upside down. Too much water will cause the mixture to slide down the wall rather than stick in place.
  4. Boil water in a large pot.
  5. Mix half a cup of powder tapioca in cold water for every 5-gallon bucket of dirt. A guesstimate is fine as we are not building a piano.
  6. Pour the mixture into the pot of boiling water and reduce heat to a simmer.
  7. Stir until the clear mixture turns milky white.
  8. Remove from heat and add to the mixed mud.
  9. Mix it all together for a homogeneous solution and you are now ready to start slapping it on the walls.
Mix soil, water, and tapioca with a hoe
Mix soil, water, and tapioca with a hoe

TIP: Do not try to mixe more than five 5-gallon buckets of adobe mud at once as it requires more effort, takes longs, and will zap your energy before you even start covering the walls.

Steps For Applying The Mud Mixture To Earthbag Walls

For better adherence of mud to the walls, you can add mesh such as a wire screen to the earthbags using nails. I had wire screens and planned to add them after the first “leveling” coat, but I got lazy and did not bother with it. The cob seemed to stick and hold well and five months later all is still good.

  1. Fill a 5-gallon bucket and carry it to where you plan to start covering your wall.

    TIP: Start in the shade and work with the direction of the sun so that you stay cool and the wet cob mud stays in the shade. If the sun hits the cob mud it will dry too fast and crack substantially.
  2. Start, if possible, on the least visible wall as your skills will improve quickly.
  3. Start applying the cob to the crevices between the earthbags at the bottom of the wall and cover a comfortable width that you can reach without moving sideways. For me, this was about 3′ as I use both hands.

    The objective of this coat is to make the wall more flat. Experiment with how thick you can pack the mud in between the earthbags and keep in mind that the thicker the mud the more cracking. And more cracking means a weaker structure and more likely to have chunks fall off even after the wall is dry.
  4. Work upwards until you finish at the top of the wall.
  5. Move to one side and repeat.
  6. Once the first coat is complete you can add the option of wire mesh or similar.
  7. Start the second coat in the same location that you started the first coat.
  8. Work from the bottom to the top again and this coat will be very thin over the exposed and protruding earthbags and thicker in between the earthbags. This coat will also help to level the walls.
  9. A third coat is likely going to be needed and also possibly a fourth. The wall becomes more level/flat with each layer.

TIP: Each new coat should be thinner than the previous to reduce cracking and the wall becoming more flat with each layer.

TIP: If you live in a very hot location, or have cold winters like where I am from, you can easily increase the wall thickness to make the interior more comfortable during extreme temperatures.

I had a lot of dirt remaining (I bought six truckloads of soil) so I shoveled a lot of it up against the lower portion of the walls during construction. This also provided a ramp for getting up onto the top of the walls for laying earthbags.

This also helps to direct water away from the house and reduces makes the interior quieter with the thicker walls.

I like the color and natural look of the earth-covered walls for the interior and the exterior. You can paint the walls or you can hire a company to spray stucco for a different look.

TIP: To better protect against insects such as ants, termites, and scorpions you can add a lime/sand, stabilized cob mud, or concrete final coat. I may actually do this as I have one or two more coats to add to my walls.

Stucco

Once the walls are smooth you can call companies to take a look at the house, discuss finish and color options with you, and provide a quote for applying stucco for a beautiful finish.

Concrete

This is an option, but not one I like. What is the point of building an earthhouse if you cover it with concrete?

Disadvantages of Concrete Include:

  • Not environmentally friendly as it takes a huge amount of energy to produce.
  • Will crack as the walls settle and concrete repairs are more difficult than slapping on more mud to cover cracks.
  • Much more expensive.
  • Ugly, but it can be painted. But again, concrete and paint cover the earth walls. If I painted or applied stucco to my earthbag house here in Thailand it would look the same as many other houses that are constructed with concrete blocks and covered with painted stucco.

Lime/Sand

A lime and sand mixture is a good method that reduces the chances of insect infestation when compared to my mud covering due to it being harder and insects prefer mud, at least in my earthbag house.

In the video below the family uses a cement mixer (cheaters! I would have used one if one was available here in this remote area) and mixed three parts sand to one part lime and water as needed.

It is easier and faster to just use your hands rather than a brick trowel.

TIP: Gloves are a good idea when working with concrete and lime due to health concerns and it will cause super dry hands.

I am not sure how many coats of mixture they added to the interior of the bedroom but I am sure it was at least two. They used drywall compound for the final coat and I am curious about how the drywall mud will hold up.

TIP: Only use drywall compound on interior walls as it will quickly absorb moisture and slough off exterior walls.

I spent many years as a drywall taper/crackfiller so I found this option interesting and may do the same for my earthbag house.

You can paint the interior walls the same as any typical wall using interior latex paint. The drywall compound will absorb a lot of paint so two or three coats are required.

The below video shows adding mud to the exterior of a round earthbag house and looks just like what I did earlier this spring. I like how they are using a drywall hawk to hold the mud!

Advantages of Earthbag Walls

  • No baseboard or window and door trim is required. I love this advantage. I am not a fan of installing MDF baseboard and trim as it is basically fine sawdust. I miss the old days with real wood trim.

    The products the manufacturers are creating now are hideous and cheapen the look of houses in my opinion.
  • It is cheap since no lumber, insulation, vapor barrier, drywall, baseboard, or trim is required. This saves a LOT of money on material and labor.
  • Less chance of growing mold. Cheap MDF trim is more likely to grow mold between the back of the trim and the wall in a humid environment.

    Drywall is even worse as it is an inert material (gypsum) covered in paper. If you ever owned a house with a damp and humid basement you likely found mold growing on the walls behind the baseboard and near the floor in corners.
  • Much more environmentally friendly, especially if using only soil, sand, and other natural products. No VOCs from the acoustical sealant or MDF glues, and no glass shards from the fiberglass insulation.

If you are curious about how much money you can save building with dirt check out my costs for various size houses for adobe construction here. Earthbag costs will be very similar.

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