BuildingHow to

Slip Straw, Earthen Floors, and Tadelakt: A Recipe for a Perfectly Natural Home

How to build a home using the dirt beneath your feet

Only a few generations ago, the vast majority of people around the world made their home with nothing more than the dirt beneath their feet. Today, unfortunately, most of that knowledge has been lost as the modern-day construction industry, along with repressive building codes, has been granted a monopoly on residential home construction. For people looking for a way to build a home without the $350,000 mortgage and host of dangerous chemicals off-gassing into their home, below we offer a simple strategy to build a home almost entirely from the mud that can be found on your building site.

Slip straw walls

Slip straw is an easy and energy efficient way to build lightweight homes or walls. It uses materials that are almost always locally available and also offers quality insulative properties. To build with slip straw you will need an abundant supply of straw, clay and some sort of wood for the structure and form work.

The straw you use should be from some sort of grain such as rice, wheat, barley etc. Hay, which comes from different types of grasses, isn´t suitable since it is usually much thinner than the thicker stalks of grain-based straw and contains seeds which could potentially sprout in your wall.

The first step in slip straw construction is to build a timber frame for your home. Since slip straw walls are light weight, they are only usable for infill walls and can´t bear the weight of a roof. Once your timber frame is finished, you need to set up a form (discarded plywood from a construction site works great) that is around four to six inches thick. The thicker your wall, the more insulation capacity it will have.

According to one website, homes insulated with straw bale can have insulation values of anywhere between R-30 to R-35. A six- inch slip straw wall, which is around a third the thickness of a traditional straw bale wall, would have an expected R value of around R-12. Since most structural, exterior walls offer essentially zero insulation, this type of wall will drastically increase the thermal performance and energy efficiency of your home when standard insulation is used on the interior walls and ceiling.

When the form for your wall is ready, you will need to mix up a heavy clay slurry by mixing one part clay (high clay content is best) to two parts water. A paint mixer attached to an electric drill is a quick and efficient way to mix up the clay and water to make your slurry. You are aiming for a consistency of melted ice cream.

Take your straw and dip it into the clay slurry, making sure that all the individual fibres get coated. Then, put the clay-soaked straw (this is the slip straw) into your wall form and use a stick to compact it as tightly as you can. Continue adding more slip straw and compacting until your wall is completely “filled up”. Let your slip straw dry for several days before removing the form.

The dried clay acts as a glue that holds the individual fibres of the wall together. Your wall will be very lightweight yet strong as well. The spaces between the straw fibres are great insulation as well. When you have finished building your in-fill walls with slip straw you can plaster over them with either an earthen plaster or a lime stucco.

A beautiful natural plaster option

Whichever type of natural home you decide to build, earthen floors and earthen plasters are a great option to add character and warmth to your home.

One of the most beautiful types of natural plaster is “tadelakt”, an ancient Moroccan form of lime- based plaster. Tadelakt can be used as a plaster over earthen homes, straw bale homes, or earthbag homes. It can also be used over cinder block, brick, and other forms of modern-day construction.

To build with tadelakt, you need to first make a lime-based plaster by mixing two parts lime putty (lime powder mixed with water to the consistency of a thick milk shake and left to sit and mature for several weeks) with one part very fine sand material. Marble dust (used in Venetian plasters) is a great option, adds strength to the plaster, and can be found at most pool supply stores.

The trick to tadelakt plasters is in the process of polishing. It is a very time-consuming process as you can only do a small section of each wall at a time. Place a little bit of the lime-based plaster on your wall and smooth it so that it is flat. Once the plaster starts to set, take a small polished rock with a smooth side and begin to polish your wall repeatedly. The goal is to try and force out of all the water in your lime-based plaster. You will need to polish a small section of wall for 15 to 30 minutes with your smooth rock until the plaster is smooth and dry.

Once you´ve finished plastering your wall, you can seal the wall with a natural soap such as olive oil soap and you will have a bright, smooth plaster that will make you feel as if you´re living in a polished piece of pottery. When done correctly, tadelakt plasters are waterproof and can even be used for earthen sinks or bathtubs.

Earthen floors

A home with slip straw walls and tadelakt plasters wouldn’t be complete without an earthen floor. Earthen floors offer a huge source of thermal mass that works great to capture the heat of the sun. When combined with passive solar design, an earthen floor can capture enough heat to keep homes warm even during the coldest winters. Slip straw walls add extra insulation to keep that heat in the house.

To build an earthen floor, follow the simple construction method below:

  • Fill the perimeter foundation of the living space with one-inch of washed and cleaned gravel. Be sure not to use surfacing gravel, which is commonly used on roads.
  • Pour a one-inch-thick layer of sand over the gravel.
  • Cover the sand with a layer of 30mm plastic sheets.
  • Pour another one-inch-thick layer of sand over the plastic. The sand on both the bottom and the top will protect the plastic sheeting from being torn by the gravel.
  • Pour about two inches of road base on top of the sand. Spray it lightly with water, tamping down the road base by hand until it is tightly compacted. Add the road base in this manner until you have about a five-inch layer of road base.
  • Mix together six parts sifted sand, two parts sifted clay and one part finely cut straw in a wheelbarrow. The amounts of each material vary depending on the size of the room.
  • Spread a two-three inch thick layer of the adobe onto the floor. Let dry for at least a week. It will crack.
  • Once dried, lay another one inch thick layer of adobe onto the floor using a trowel to create a smooth finish then leaving it to dry for another week. It should crack significantly less.
  • The final layer should be no more than half an inch thick and applied with a trowel to give a fine finish. Let dry completely.
  • Once dried, apply linseed oil to the entire floor with a rag. Make sure to put down as much oil as possible without creating puddles. Let dry, which can take a couple of days.
  • Mix three parts linseed oil with one part oil thinner, and apply the mixture to the entire floor. Let dry completely.
  • Mix two parts linseed oil with two parts oil thinner, and apply the mixture over the second layer. Let dry completely.
  • Mix one part linseed oil with three parts oil thinner and apply the mixture over the third coat. Let dry completely. It is important to make sure that between coats, the oil is completely absorbed into the floor.
  • To seal the floor, one can add melted beeswax as well.

Modern-day homes most likely have VOC-emitting paint that is applied to drywall that covers a stick frame built from pressure treated 2x4s and formaldehyde-laden plywood. Floors are covered either with polyurethane carpets that are sprayed with cancer causing fire retardants or laminate flooring made from MDF, which is also a major source of formaldehyde that off gasses into the home. This construction process essentially ensures that you will be living in an environment where the indoor air quality is overloaded with volatile organic compounds (VOCs) that have the potential to negatively affect your health.

A home made with walls sourced from local clay and straw, with beautiful hand-polished walls with lime and sand, and a floor made from the earth beneath your feet will not only be beautiful and aesthetically pleasing, but will also offer a healthy, natural environment for you and your family.

Tobias Roberts

After working in the development industry for over a decade, Tobias decided it was time to stop advising Central American farmers how to do things if he didn´t have a piece of land to live coherently with what he taught. Together with his family he runs a small agro-forestry farm, tourism cooperative, and natural building collective in the mountains of El Salvador.

4 Comments

  1. Tobías, this is a clear explanation from you. I wish I were 20 years younger to build the house of my dreams following your instructions. I’ve got the plot and the materials but I need someone to help me to build it.

    Thank you for inspiring the world.

    Valentina

    1. Me too, 20 years less and things could be easier, especially for house building. But for a food fforest, it should be possible, with a big load of covering, and green fingers. I am going to try, any how. The house is a matter of renovation, in the most ecological way possible.

  2. Tobias what a great ‘how to’ article. I am very inspired & think I might try it in our shed as a place to practice. Hemp is a fibre often talked about so I am wondering if you think the wall technique might be the same in place of grain based straw?
    Regarding the adobe floor could you please clarify:
    1. Why is it important to build up the perimeter foundation (I assume you mean the perimeter of the floor area?)
    2. After completing ‘the perimeter foundation’ is it correct that the adobe is put onto raw ground but spread out to this foundation?
    Any thanks
    Techa

  3. Use this information with caution:
    According to one website, homes insulated with straw bale can have insulation values of anywhere between R-30 to R-35. A six- inch slip straw wall, which is around a third the thickness of a traditional straw bale wall, would have an expected R value of around R-12.

    These R values are in imperial units, used in the USA, and are also on the exaggerated side.
    To get Metric values divide by 5.68. And even then the achieved R value will depend on the density and thickness of the wall. R value for strawbale walls is often overstated, and there is a lack of reliable duplicable testing, but R-30 imperial (or around R 5 metric) is probably optimistic, and a 6 inch or 150mm thick wall of clay slip /straw will have an R value closer to 1.2 to 1.5 metric or 7-10 imperial.

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