How to Make Adobe Mortar

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Mixing adobe mortar is hard work but can be fun.
Mixing adobe mortar is hard work but can be fun. (Image: adobe2 image by SHERNA from Fotolia.com)

When building an adobe home, it is best to use the same material for the mortar as you do for the bricks. If you purchase adobe bricks from outside your region, you can easily mix adobe mortar from materials close to home. All you need are simple tools like a shovel and wheelbarrow, though a mortar mixer will make the work easier. Unlike concrete, adobe mortar is not caustic and the biggest danger from splashing is an impromptu mud fight.

Things You'll Need

  • Shovel
  • Clay
  • Masonry sand
  • Water
  • ¼-inch hardware cloth
  • Wire cutters
  • 2-by-4-inch lumber, 1 stud length
  • Circular saw
  • Roofing nails
  • Hammer
  • 100-gallon stock trough (optional)
  • Mortar mixer
  • Wheelbarrow
  • Trowel
  • Mortar hoe
  • Garden hose
  • Spray nozzle

Preparing Material

Cut a piece of hardware cloth wide enough to hang over the edges of your mixing trough, to make a screen. You can use a stock watering trough or other similar large, sturdy container. Cut the 2-by-4-inch stud into two pieces. Wrap one end of the hardware cloth around each and secure with roofing nails. Place the screen over your mixing trough. If you are certain there are only very few rocks larger than 1/4-inch in diameter, you can skip the screening step.

Shovel clay into the trough. Press clods through the mesh but do not allow rocks to pass through. Shake off rocks after every few shovels.

Soak the clay overnight if possible, or for at least one hour. Add just enough water to wet the clay. The clods will break down and absorb the water. If you add too much, you will have to wait for it to dry out before you can mix the mortar.

Mixing the Mortar

Add water to the mortar mixer. While the machine is running, add the clay. Allow the clay and water to mix for a few minutes, then add the sand. The exact amounts of each material may vary, but an ideal mix is composed of 25 percent clay and 75 percent sand. In general, a ratio of 4 gallons of water, seven shovels of clay and 21 shovels of sand will fill a wheelbarrow. If you only need a wheelbarrow or two of mortar, or if you do not have a mortar mixer, you can simply use a wheelbarrow and mortar hoe. A mortar hoe is larger than a regular garden hoe, and has two holes in the flat part. Add materials in the same order.

Run the mixer for several minutes. The mortar should just hold its shape when squeezed into a ball or when shoveled onto a layer of adobe bricks. If the mixture is too wet, run the mixer longer. If it is too dry, or if it is very hot outside, you may have to add water.

Tip the drum with the mixer running and allow the paddles to push the mortar into your wheelbarrow. You may find it helpful to have a helper for this step.

Spray with a garden hose and spray nozzle for clean-up. To prevent rust, rinse all your tools when you are done for the day. If the mortar dries on your tools overnight, you will still be able to clean them with just water.

Tips & Warnings

  • You may be able to use native soil if it approximates the ideal mix (25 percent clay and 75 percent sand).
  • Adobe is an extremely forgiving material. If the mortar dries out while you are working, simply add water. Add much less water than you think you may need, as it is easier to add more than to wait for the mix to dry out.
  • Pay attention when using a mortar mixer. Never reach into the drum while the mixer is running. Always close the lid so it does not fall down onto you. Wear safety glasses.
  • If you do not remove stones larger than 1/4-inch in diameter, they can act as ball-bearings and break the adobe bricks above or below. You can also flick stones out with a trowel as you spread the mortar and stack the adobe bricks.

References

  • “Adobe Build it Yourself”; Paul Graham McHenry Jr.; 1985
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