«The Cob Builders Handbook You Can Hand-Sculpt Your Own Home Table Of Contents: Acknowledgements and Warning INTRODUCTION What is cob? Why build ...»
Remember, the ground outside can be lowered as you dig soil for constructing the wall. Make sure the ground slopes away from your home in all directions.
Making the floor Tamping the ground It's easiest to decide the floor height(s) early on in the design and construction processes. That way you can do the rough leveling of the floor area before you start to build. It's also best to decide what kind of floor you are going to make before you start building, so you can dig down to, or fill in to, the appropriate height. If you leave it until after the builders have tramped back and forth across the ground, it will be a lot harder to dig the dirt out to level it.
Scrape off the topsoil in the floor area and put it where your garden will be. Any subsoil that you dig out of the floor area can be used for making cob. The building process and all those feet will help do a lot of the tamping work for your future floor.
If you are building up the floor level, you can do that before you build or anytime during the building process to make the most of the tamping feet of the builders.
Go over the ground and each layer of floor base with your tamper. You can't tamp too much. You may even want to rent or borrow an electric powered vibrating compacting machine to save you work.
To help you estimate a level floor surface, use a long level, string level, or water level.
If you use a long level, sit it on top of a straight 2x4, like you used for getting the slope for the drainage. (See the illustration on page 31.) using and designing a water level Attach a 3/4 inch clear plastic hose to a container, a bucket, or an old kettle. Put a clamp or a tap on the hose so you can open and close the flow from the container to the hose. Set the container in a secure spot where it's above the highest point on the floor area. Fill the container with colored water. Hold the free end of the hose above the container and open the clamp so the colored water can flow into the hose. The water in the hose will always seek the same level as in the container, so you can establish even floor heights by measuring down from the water level in the hose all around the floor area. There are other types of water levels. Any sort will do the job.
marking your estimated floor height
Knowing the floor height will help you measure the heights of the counters, seats, windows, etc. as you build. Mark the future floor height on stakes pounded into the ground inside the floor area. If you plan more than one floor height, mark each one with stakes. Put the stakes somewhere out of the way because they can be perfect toe stubbers! Once the foundation is made, the floor height can be marked along the inside of the foundation with a chalk line or pencil. Give yourself plenty of space on either side of a door before raising or lowering the floor level.
Base (or layers of base materials) under the floor (See illustration of layers that make up the floor, on page 57).
Reasons for putting a base under the floor: Usually the floor needs to be filled in so that it is at least 2 or 3 inches • higher than the outdoor ground level to insure it will stay dry. You may have to bring in some fill to raise the floor. It's OK if the floor's base makes the floor higher than the foundation, and makes the floor butt up against the cob walls as long as you've planned for this when placing the doors, and heights of the seats and counters.
The base is made of stabilizing materials that flex, minimizing the stress • on the floor when the ground moves.
The base provides a little insulation which speeds up the time it takes the • heat to be reflected back into the house.
Moisture barrier between the ground and the floor? The general rule with natural building is to avoid moisture barriers if possible. With good drainage design and an adequate gravel base, your floor shouldn't need a moisture barrier.
Floor base tests You can make floor base experiments in 4 or 5 inch plastic potted plant containers.
Fill them with the materials you have available, and tamp each layer. Then push them out of the container molds. See which are the toughest. Regardless which base you decide on, tamp, tamp, tamp!
Floor base options the ground as a base It is possible that the ground is OK just as it is. A good drainage system around the house should keep your floor dry. Some soils are very stable and drain well and an added base may be unnecessary. Remember that the finished floor needs to be higher than the outside ground level.
gravel as a base There's this great stuff you can get at the concrete supply place called road base. It's what's used under the roads for drainage and stabilizing. It is crushed rock in various sized pieces, usually 3/4 inch on down to powder (called "3/4 minus" in America).
Four inches (or more) of road base, dampened and tamped, make a very stable and very cheap base for your floor. Some people sift it and put down layers of the different sized particles that separated out, starting with the largest and layering up to the smallest sized particles.
Remember to tamp it well. If you live where the ground water level is high, you may want to make an extra thick (10 inches or so) base or a layer of large gravel and a layer of road base. The gravel will discourage water from wicking up into the floor. If you use a thick base for your floor, it is important to make your ceilings that much higher too.
sandy or silty soil layer as a base
A leveled layer of dampened, tamped, sandy or silty soil, two or three inches thick, is sometimes used as a base or as an added layer on top of the gravel or road base layer. This needs to have enough clay in it to bind itself together when it's dry. If you are making a floor of flat stones and bricks, the sandy or silty soil makes a good bedding for them.
You can put pipes under the floor to heat your house. Hot water circulates through the coils of pipe, heating up the floor and the interior space. I have never done a floor with heating coils in it, but there is information available on putting heating pipes into concrete slabs. You can modify this information using natural materials. If you want to bury pipes under the floor, you can put them in this soil layer, but only if you are not adding a screen layer that will insulate the heating pipes from the interior.
optional screen layer
Some natural builders put a 3 or 4 inch layer of tamped light clay/straw (see page 143 for instructions on making light clay/straw) over the gravel before putting down the soil. This prevents the soil from sifting into the spaces between the chunks of gravel and adds a little layer of insulation. The light clay/straw is tamped well or compressed when you tamp the soil layer. It will crush down to an inch or less. Loose straw or old sheets or newspaper would serve the same screening purpose, like on top of the drainage ditch. If you are troweling a cob floor right onto the base, you won't need to worry about it filling in the air spaces between the gravel.
Other possibilities for an insulating base layer are to mix clay slip with vermiculite, perlite, or pumice.
Cob floor surface A one-piece cob floor is the longest lasting type of earth floor. The floor surface sits on top of whatever you've decided to use for the base layer.
You can make a floor with one 3/4 inch layer or two 1/2 to 3/4 inch layers of your cob floor mix (with optional additives) thinned down to a consistency that can be troweled on. Make it as dry as possible but wet enough to trowel. The less moisture there is when you lay it down, the quicker it will dry and the less it will crack.
Keeping your trowel wet while working on the floor will make it a lot easier to smooth the surface.
Floor surface recipe The floor is basically the same stuff as the walls, sometimes with extra sand added depending on your original mix. (See page 72 for proportions for making cob.) Sift all the ingredients quite finely for the final layer of floor.
If you use straw in your floor mix, chop or grate it finely. Use shorter pieces of straw and less if you don't want it to show in the floor surface. The straw can be grated quite small. (See page 153 for information on how to break up the straw.) If you have a clay rich soil and a shortage of sand, use more straw instead of the sand.
Some natural builders don't use any straw in their floors. Make tests until you find a recipe that works.
Possible additions to a standard cob mix for floors Go over the section on plaster additions (pages 154-156) and apply that info to the floor mix.
glue. Adding a little Elmers glue helps harden the floor.
ground psyllium seed husk. This is a wonderful addition to a cob floor! Have you ever noticed tennis courts or tracks that feel like "soft" concrete? Psyllium gives them that soft, rubbery feel. This makes the floor easier on your legs and on your dishes. A little bit of this stuff goes a long way. Too much will make it hard to trowel. Make up some test batches with different amounts of this additive in each until you find the percentage that works best. For a 12 foot diameter round room, you'll need about a pound of psyllium.
manure. A very common ingredient for earthen floors in many parts of the world.
This can be used as the fiber in your recipe.
blood. Ox blood is a common ingredient in old floor recipes. It's supposed to make the floor a lot harder. These days you can buy blood meal at plant nurseries. Use this on the top layer.
wood ash. This is an additive that I have come across in old literature. I haven't tried it yet.
flour. Like with plaster, the addition of flour paste will harden the surface.
test batches for the floor surface Try out different floor recipes before you decide which one(s) to use. Do lots of tests.
Outdoors, make little samples of the base material and trowel the test mixes onto it. A two foot round sample will be plenty. Let the samples dry, protecting them from direct sun and from rain. How do they look? See how they hold up when you walk on them. Once you've narrowed down what works, make some larger test batches of the same recipe to make sure it's the one you want. You can try out your homemade sealants (see page 66) on the samples too.
Make test batches varying the ratio of sand to clay, until you come up with a recipe that doesn't crack and holds up when you walk on it. Cracking means too much clay, and too much sand will cause the floor to slough off when walked on. If you are doing more than one layer, you can make the bottom layer 75-85% sand and small gravel.
Putting down a cob floor Ideally, you'll be able to trowel down each layer of the whole floor in one day. You can mix up enough material for the whole floor layer a day or two ahead of time and let it cure. For a big floor, start in the morning so you'll have the whole day to put it down if you need it.
Make sure the base for your cob floor is as clean as possible. The base then needs to be dampened. Otherwise, the dry material under the floor will suck the moisture out of the floor quickly, and it will be more likely to crack. Spray it lightly again and again so it soaks in well but doesn't create puddles.
Start laying the floor furthest from the door, working your way toward the door.
That way you can get out without walking over your beautifully troweled floor. Oops!
Working back and forth across the floor, add a 1/2 to 1 inch layer of floor mixture in reachable swathes (2 feet or so). Leave the edge slanting toward you (45 degreesish) and scratched to make a rough surface for the next strip of fresh floor mixture to adhere to. Spray the slanting edge with water when you're ready to attach the next bit to it. Lay your next strip of floor, etc., etc., until you're done!
57 Around the edges, where the floor meets the foundation or the walls, is a tricky place. The already dry walls quickly sap the moisture from the floor where wall and floor touch.
Sometimes the floor will shrink away from the walls as it dries, leaving a gap there.
You can take some of your floor mixture and let it dry a little, or mix in some dry ingredients until it's as dry as it can be and still be malleable. Squish this together in your hands, roll it into a sausage shape, and put it down around the edges of the floor.
Trowel it flat as you do the rest of the floor. The drier mix will minimize the shrinkage. (Thanks Athena! Good idea!) After the first layer of floor has hardened to the leather-hard stage, you can add the next layer. When your last layer of floor has hardened to the leather-hard stage, go back over it with a squirt bottle and trowel if you want a glossy smooth finish.
Stand and work from plywood squares to minimize footprints.
If you've used too much clay and the top layer cracks, you can add another very thin layer of floor. Remember to dampen what's there before applying the next layer.
How to connect one day's floor work to the next Sometimes it turns out that you can't do the floor in one fell swoop, or that you need to join the floor of a new addition to an old floor. Where the floors connect is a potential weak spot. If you know you'll be adding on to a floor, make sure you leave the edge sloped and scored well. That means scratch it up so the surface is rough and the next layer will be able to key into the scratches. When it's time to add on, wet the sloped edge really well and trowel down the new floor.
Save some of your original dry mix so you can use it for repairs later on.
Leveling the floor The floor doesn't have to be exactly level. Slight undulations make a floor feel more natural and friendly. Have you ever seen anything (other than water) perfectly level in nature?
Establish where you want the floor height, and draw or snap chalk lines on the walls or foundation to guide you when you're troweling down the floor.