«The Cob Builders Handbook You Can Hand-Sculpt Your Own Home Table Of Contents: Acknowledgements and Warning INTRODUCTION What is cob? Why build ...»
You can use a 2x4 with a level taped to it, and drag it across the wet floor to "scrape" it level. You can lay down guides running parallel to each other and close enough for the 2x4 leveler to span. These can be made of thin stops of the floor mixture or thin strips of wood that need to be removed as soon as possible and the gap they made filled and troweled.
Here's a little trick to prevent you from getting too far off level. While you are putting the base in and/or troweling the floor surface, nail big headed nails into the ground with the tops a tiny bit lower than the final floor height. Start with one nail and level the tops of the other nails to it and then to each other. Put them as far apart as your longest level will reach. This will give you a guide while you are putting down the
Drying your earth floor After you've put down your floor, let it dry completely. This will take a few weeks, depending on your climatic conditions. It's best to stay off it. Protect the floor from direct sun and from freezing. A layer of loose straw will help protect the floor. This will slow down the drying some, so you may want to remove the straw when the conditions don't warrant protection. If you live where it's hot and dry, it might be a good idea to cover the floor with tarps or straw during the day to slow the drying and minimize cracking.
If you have to walk on the floor while you're working on it or before it's completely dry, put down 2 foot squares of plywood and step on them or you'll have footprints.
This is a good time to get firewood, put the gutters up, work on the drains, finish the porches, plant the fruit trees, visit non-cobbing friends and family, or go sit down and read a book.
Sealing an earth floor The sealant for earth floors needs to soak into the floor rather than forming a hard (crackable) skin on top of the floor.
floor sealant recipe The basic recipe is boiled linseed oil (if you have an aversion to linseed oil, you could try other oils, possibly coconut?) and solvent (turpentine, mineral spirits or a citrus solvent). The solvent thins the oil and helps it soak into the floor. This sealant looks good on stone and brick too. Experiment!
CAUTION!! Oils and solvents are very flammable and can spontaneously combust. Be careful!
The first coat can be pure oil, because at this point the floor will be very porous.
Adding solvent helps it soak in after the previous coat has made the floor less porous.
The second coat can be 3/4 oil to 1/4 solvent. The third coat can be 1/2 oil and 1/2 solvent. The fourth coat can be 1/4 oil and 3/4 solvent. (This last mixture can be used whenever you want to increase the shine of the floor, like maybe once or twice a year.) putting the sealant on the floor Let the floor dry thoroughly before sealing.
Put the coating on with a paint roller or a large brush. Use a brush around the edges just like you would if you were painting. Let each application dry, then put on the next one. Apply as much as the floor can absorb and no more. If it puddles on the surface, mop it up.
If you want a really polished look, try heating up beeswax mixed with a little solvent and oil. Paint this on as a final varnish for the floors. Experiment on your floor tests, or in out-of-the-way places on your floor until you come up with a finish you like.
Caring for a cob floor This kind of floor is softer than what you're probably used to and will require gentleness. Pad the feet of the chairs so they don't gouge the floor. Take your high heels off at the door. Don't drag furniture across it. Use your common sensitivity. One good thing about a softer floor is that it will be gentle on your feet and legs.
Repairing a cob floor
If the floor gets a ding in it, or if one of the cracks starts to enlarge, it's best to patch it as soon as you can. Holes grow when walked on. It's the same philosophy as, "a stitch in time saves nine." Dig the hole out, creating a bigger hole with the edges slanting so that the bottom of the hole is wider than the top.
Moisten the hole well and patch it with the mix that you saved from the original floor for just this purpose. Seal it like you did the original floor once the repair has dried.
If you know you'll be hard on the floor in certain areas, you can put rugs down to protect the heavy wear spots. You may want to make the floor out of something more durable in those places, like brick or stone.
Some other floor surface options flat stones These can be set into a silty or sandy soil layer. Put the flattest sides up. The stones can be laid with or without mortar between them. You can use a cob, soil cement, or concrete mortar to fill in the spaces between the stones or bricks. (See the section on mortars in the chapter on foundations, pages 50-51.)
Bricks are expensive if you buy them new. See if you can scrounge up some used ones. Old bricks have become popular and are harder to come by than they used to be.
Good luck! Bricks can be used with or without mortar. They can be laid slightly crooked to each other to create a flowing pattern that will suit organic-shaped walls better than the usual parallel rows.
Some earth floors are made thicker and with a heavy clay content. This type of floor is often wetter and is poured into the house. If it is wet enough, it will level the surface itself like water would. Some folks mix the floor right in the house, throwing the ingredients in, adding water, and treading it in place in a big, muddy party.
This kind of floor is allowed to crack up naturally and then the cracks are filled in with a different colored mortar to create a flagstone look. The partially hard floor can be cut into tiles or shapes to give it a controlled place to crack, and then those cracks can be filled. The 'grout' or mortar can be thinned down and drizzled from a pitcher or tin can into the cracks.
This type of floor is usually 4 inches thick, either poured all at once or in two 2 inch layers. It will take a long time to dry - so if you live where the humidity is high, you'll probably want to decide against this kind of floor.
rammed earth A floor can be made of rammed earth. Cob ingredients (minus the straw) are mixed well and laid down almost dry (ever so slightly moist) onto the floor base. Tamp the earth really well with a flat tamper. A good floor tamper can be made by welding a 12 inch (or less) square flat piece of steel onto a steel pipe, or by screwing a 12 inch (or less) piece of plywood to your wooden tamper. I suggest you make tests in potted plant containers and see what you think. An advantage to this type of floor is that it will dry quickly. Although it is not as durable as a cob floor, it is good under tile or carpets.
(See page 52 in foundation chapter for more about soil cement.) Make up test batches as if you are mixing cob, but add different amounts of cement to the dry ingredients.
You'll probably want a soil cement floor to be at least 4 inches deep. Try tamping some of the tests. Dry the samples. Did they crack? Are they strong enough to walk on? The surface can be cut, printed, or pressed to look like tiles or shapes. The spaces between the tiles can be filled with a different colored soil cement to look like grout.
Soil cement can be used to make tiles. Both these tiles and the poured soil cement can also be used for the floors of patios and porches.
You can use a rototiller to make soil cement floors (or even roads) if you have a sandy soil. Figure on making them 5 inches deep. Calculate how much cement to add (6 to 10%) to each square yard or meter.
tiles Tiles make a very beautiful flooring. They are expensive in some places. You can always get seconds or broken tiles and make a mosaic floor. Broken organic shapes look great with the rounded walls. You can make your own tiles out of soil cement, fired clay, concrete or even wood.
wood To make a loft or second-story floor, simply bury the supporting beams and/or joists into the cob.
You may want to put the floor in as you build. That way, where the cob wall and the floor meet, the squared ends of the floor boards will be buried in the cob wall. This makes the finishing work easier than cutting curves on all the boards if you put the floor in later. The floor will serve as a scaffolding while you cob the second story.
Protect it so it doesn't get wrecked during construction.
I have never built a wooden floor on the ground floor of a cob house. To me that would waste the opportunity to have a thermal mass floor that offers heat storage. It would also use precious wood. If you do decide to make a wood floor you might want
to consider the following:
COB GLORIOUS COB!
I suggest you read through this chapter once before you try cobbing.
How does cob work? Soil usually contains sand and clay which are the main ingredients of cob. Cob is sand 'mortared' together with clay and strengthened with straw. Imagine the cob as a miniature mortared, reinforced, stone wall. The sand particles, like the stones in a stone wall, provide strength. The clay serves as the mortar. The straw does the reinforcing job of the rebar (reinforcing steel).
You will be sculpting a semi-liquid that will turn to "stone".
The recipe for cob is pretty flexible. Lots of variations work well.
Materials vary so you'll have to make up some test bricks until you find the best recipe for your ingredients.
The amount of straw is hard to quantify. I like to add as much as I can, until each piece of straw is surrounded by the earth mix. You'll need to stop adding straw before there's too much straw, or the cob will fall apart. The more clay in the mix, the more straw you can add. Try it. You'll get a feel for it. Read on for more details.
Test your soil Soil is made up of various sized particles: tiny stones, sand, silt, clay, and organic matter. To find soil suitable for building material, first scrape away the top organic layer. Use this top soil for nourishing your garden plants. Examine what's underneath.
You will be able to tell a lot by feeling and looking at the soil. Can you recognize sand particles and sticky clay?
Take a cup or two of soil from various potential house sites and from various depths.
(Soil samples can vary a lot even a few feet from each other.) Take out any stones or pebbles. Put each sample in a quart jar. Label each jar, recording the depth and where the soil came from. Then fill the jars 3/4 of the way to the top with water. Shake well.
I mean really well. Shake that baby! Then let it settle. If your soil has sand, silt and clay in it, you'll get three distinct layers.
The sand is the heaviest and will sink to the bottom immediately as you watch. The silt will settle next, more slowly, and the clay will stay suspended in the water for a while then settle on top of the silt.
Start out by making test bricks using just the soil from your site. If you need to import materials, stretch the recipe to use as much of the on-site soil as possible. Too much clay in the cob mix will make it shrink and crack as it dries. Too much sand in the mix makes the cob crumbly and hard to sculpt, and when dry, sand sloughs off if you touch the cob. If you run into these situations, you'll know you've stretched it too far.
Depending on your materials, recipes with as much as 50% clay and 50% sand or as little as 15% clay and 85% sand can work.
Making Test Bricks To figure out a good mix for your soil, make up some test bricks. Try various recipes and combinations, making sure you label each one carefully so you can reproduce the best ones.
Make your first couple of test bricks out of the soil from the site or from where you've dug out for the foundation. If you're lucky, you may have a soil that works for cob as it is without adjusting the sand/clay ratio. After the jar test, you'll have some idea what you might want to add for the other test bricks. Make tests adding more and more sand until you've stretched it to the point of too much sand. You'll be able to recognize that point because the mix won't hold together well and will be hard to form into bricks. The sand will slough off when you rub the dried brick. You can take the experiment to the opposite extreme and add too much clay so the brick cracks while drying. You will learn a lot doing these tests. Make three samples of each sand/clay mix, adding different amounts of straw until you get a feel for how much you need.
When the bricks have dried completely, have a look at them. Eliminate the ones with the biggest cracks because they have too much clay in them. Does the sand come off when you rub the bricks? If so, those have too much sand. Try breaking the others.
You can drop them from one or two feet up to test their strength. The ones that are hardest to break are the best recipes. Leave them out in the weather or simulate some rain and observe which ones are the most resilient. Analyze what amounts of straw made the strongest bricks. Now you have a good basic recipe. Lots of variations will work just fine, so don't be too much of a perfectionist about all this. You may want to stretch the recipe so you can use as big a proportion as possible of the soil you have on-site.
If you want to reassure yourself and do a more extensive test, build a garden wall, an outdoor sculpture, or a bench, and observe how hard it dries and how well it weathers.
Remember, your walls will be protected from the rain by a roof.
More details about cob ingredients SAND Sand particles are the main building blocks of cob. Ideally, each particle will have rough angled sides so the sand pieces interlock with each other, helping to hold the cob together. If the sand particles are rounded and smooth like ocean beach sand, they'll be more likely to slide off each other.