Recently, we built our bathroom addition using adobe bricks. The mixture for adobe bricks use is similar to that used to make cob walls. Unlike cob walls, however, which are constructed using a wet material, adobe bricks are molded wet, and then sun-dried to use when they’re hardened. For this reason, adobe bricks are much more commonplace in areas that experience hot, dry periods during the year. Mediterranean climates are one example of where adobe can work well (including California, Southern Australia, and elsewhere), as well as parts of Central America.
With bricks, you can build as high as you want in one day, whereas with wet cob, you’re limited by how quickly the wall starts to slump under its own wet weight. For this reason, hot, dry locations can take advantage of the drying effect of the sun, and I encourage those living and building in these climates to consider using dry adobe bricks to build structures.
Make Your Own Adobe Bricks for DIY Construction Projects
Build a Wooden Mold
First, you’ll need to make a mold using any material available to you, or that you know how to work with. We make ours using wooden boards, but metal or plastic would work just as well, and possibly be more durable too. You can make a mold to produce one, two, or even more bricks at a time. The limiting factor really is how many you can pick up at any one time in order to drop the bricks out of the bottom of the mold.
So first, cut your wood to size. When fixing the wood together, you must make sure that each box is as close to square as possible. If they’re off even a small amount, this will make it difficult for the bricks to slide out of the bottom of the mold when they’re ready. Add a couple of handles on the ends to make it easy to lift when full of clay.
Mix Earth Material
Next up, collect your earth: A mix of 75 percent sand and 25 percent clay works well for us. Some people filter their materials first, but I’ve found that as long as there are no aggregates larger than a centimeter or so, then it’s never too much of an issue. You can add straw too, which will help reduce cracking and create a tensile strength within your bricks.
Mix Materials Thoroughly!
Then, add water. The mix should be wet enough to easily mold into a shape, but dry enough to hold its form on its own. Before you fill the mold, make sure the mold itself is wet to aid expulsion of the brick.
Fill the Molds
Throw your mix into the mold each time with some force, and push it into all the corners to make sure the mold is completely filled out. I prefer to use a slightly wet mix as I can throw it into the mold and it naturally fills all the gaps. But be aware that a very wet mix may slump after you’ve removed the mold, so do some experimenting here to get the feel of different saturations.
When the mold is full, lift it by the handles firmly to release the bricks. You may need to shake the mold slightly to set them free.
Dry the Adobe Bricks
Then, let them dry in the sun, making sure to cover them if you expect rain or extreme heat — fast drying can cause cracks — and turn them every day or two to allow for even drying. You should leave your bricks about a week after drying before using them so they can harden well.
Build!
And when you have enough bricks, you can start building. It’s estimated that an expert brick-maker can make about 300 bricks each day, including collecting and preparing the adobe. After about a week of brick-making, we got to a pace where we could make 150 bricks per 10-hour day, including collecting sand from 50 meters away and clay from 80 meters away from our preparation site.
Good luck, have fun, and if you have any questions, please email them or leave them in the comments below.
Tom Keeling is based in Portugal and has traveled throughout Brazil and Eastern Europe learning about natural building and farming. He’s working on a two-story stone barn renovation using clay and wood, and including a shower and toilet block built using rammed earth and adobe bricks. Connect with Tom at Mediterranean Permaculture. Read all of his MOTHER EARTH NEWS postshere.
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