Adobe Walls

Before you start building, it’s a good idea to test your possible adobe deposits. This comes in two stages.

1. Put some earth (take out rocks) in a jar, add water, and shake real well. The sand should settle to the bottom, then silt, then clay. The perfect mix will be 15-30% clay, 70-85% sand.
2. Make some test bricks out of each sample. Too much sand will result in a crumbly, weak brick. Too much clay will shrink and crack as it dries.

Many people use straw in adobe. We don’t. Instead, we add about 10% (20% in top and bottom layers) cement. We find it makes stronger bricks and doesn’t erode as fast in rain, giving us more breathing space before having to do a plaster.

1. Set up a canvas tarp on the ground (about 5’x5’).
2. Have buckets of water and a bag of cement handy.
3. Put 27 shovels of dirt and 3 shovels of cement (9:1) onto the tarp.
4. Mix the two together while it is still dry.
5. Pull the edges of the tarp towards the center, so that the dirt is left in a pile.
6. Hollow out the center, and then almost fill it with water.
7. Scoop dry dirt from the sides into the pool of water until the pool is covered over and looks like a volcano.
8. Jump into the volcano (we started using old boots after the water started getting cold, and our feet were torn up by small rocks) and start stomping.
9. Sprinkle water over the dirt and pull one side of the tarp towards the other side, making the dirt roll up together.
10. Stamp again and repeat the process until there is no dry dirt left and the mud sticks together.
11. You don’t want it too sloppy. Cookie dough consistency is what you’re aiming for. When it’s ready, it will form a solid log when you pull one side of the tarp.

Curing’s the process of keeping the material wet, or damp, for a period of time after it has set up. The slower it dries out completely, the stronger it will be.

For the first day, we would use a paintbrush to paint on water. This helps join the mud at the seams. If small cracks appear while the mud is still a little malleable, use your thumb to mush the mud together around the crack, and then paint it with water. We then sprayed on water for a couple of days, a few times a day.

Small cracks are no big deal. You can patch them with adobe or just plaster over them. Larger cracks that keep growing are a sign of a more serious, structural problem (like the wall is leaning).

You can use adobe for almost every part of your house – walls, floors, even roof when using bricks.

Cob is basically formless adobe. You mix the mud as you would to make bricks, but instead of pouring it into forms, you just slap it onto the wall and mold it with your hands.

The advantage of this method is that the end result seems more natural and aesthetically pleasing, lending itself more to curves and curious shapes. Your house will seem more like it was grown than built.

The downside is that it is slower. Adobe is heavy when wet and will only support a certain amount of weight before it begins to sag and ooge. Adding straw to your mix can help with this, but you will still need to make each layer fairly thin. Usually though, by the time you have put a thin layer all the way around your walls, the place you begun should be hard enough to add a bit more.

You may want to use some form of protection for your hands, whether gloves or taping your fingers, as the little rocks that are inevitably in your mud will start to painfully pit your fingertips.

When we started building, on our first property, we made a small cob powerhouse, by way of an experiment with adobe. Though it was fun and turned out real cool, we went on to use brick forms for the main house, as cob was a lot slower.

The traditional way to make bricks is to set your forms on the ground, pour wet mud into them, tamp the mud down, and then remove forms.

When the bricks have dried out and cured, you then lay them as you would any other brick, using adobe as mortar.

You can make your forms any size you wish, depending on what thickness you wish your walls to be (thicker walls means more thermal mass, so a more temperate house, but that also means more material). About 3″ or 4″ tall is the norm.

It’s nice to make forms for a half and even three-quarter size brick, so that you don’t have to cut any later.

One advantage with making the bricks on the ground is that they are easier to cure. You can stack them leaning against each other, wet them and then cover them.

The adobe bricks that we used for our home were a little different. We made much larger forms and set them up on the wall itself, pouring the bricks in place. The thing with pouring bricks in place is that, when you remove the forms, there is a space in between two bricks, where the forms used to be. We solved this by attaching two extra pieces of wood, 6” tall, to the middle underside of 2 opposing sides of the brick form. We call them T bricks, and we used for our form a wooden, box-like form, 12”x12”, 6” tall.

1. Set up the forms on the wall. If your first layer is plumb and level, each subsequent layer should be too, as the form is positioned by the layer under it. Still, it’s not a bad idea to check
2. Pour mud into the forms.
3. After about 5-10 minutes of the mud setting up (when it’s firm, but not dry, to the touch), pull the forms upwards, off the brick. If the mud is sticking to the form, push down on the corners of the brick as you’re pulling the form up.
4. With your fingers or a trowel, merge the edges of the brick into the one below it for a better join.
5. Lay one level of bricks.
6. Then, on the next level, shift the brick forms over 6” so that the l part of the T covers the gap of the level below.

We put remesh, as reinforcement, into the middle of our house wall. Because of this, we couldn’t use our T-bricks for most of it. However, we used the same principal of pouring the brick in place.

We made some large forms that bolted together on the wall.  Once the mud was firm, we unbolted and removed them. This also allowed us to add blocks of wood into the form that, once removed later, left nooks and crannies in the wall.

Because adobe is heavy, buttresses are a great idea at the corners or any other point of stress. They offer support and counter any outward forces. This will prolong the lifespan of your adobe home and make for an interesting and beautiful feature to the outside.

One of the best possible finishes for an adobe wall is a lime plaster. If you put a concrete stucco on the exterior, you will have to put a lathing on to the wall, otherwise it will eventually crumble off. However, lime plasters adhere great to adobe, are very cheap and easy to apply. They also add to the thermal quality of adobe (making it cooler inside when hot, and warmer inside when cold).

You can reapply the plaster every so often when needed, or cover it with a sealant.