«The Cob Builders Handbook You Can Hand-Sculpt Your Own Home Table Of Contents: Acknowledgements and Warning INTRODUCTION What is cob? Why build ...»
Tamping tips Regardless of what type of foundation you decide on, always tamp the soil on the your foundation trench to compress the soil and minimize future movement.
A simple tamper can be made from a heavy piece of a tree (4 or 5 inches across).
Either drill a hole and stick a dowel or pipe through the hole to make a handle, or chop a handgrip with a hatchet. Another option is to screw a piece of plywood (1 foot square + or -) onto the bottom of your tamper. The tampers can have bells or bottle caps nailed loosely to add some percussion to the tamping rhythm. (A 'tamporine'.) Another simple tamper can be made out of a 2 1/2 inch (plus or minus) metal pipe filled with packed dirt or stones and capped on the ends. You can use the special caps they make for the tops of fences. The metal pipe can have a flat piece of steel (1 foot square, + or -) welded onto the bottom. The smaller the bottom of the tamper, the more pounds per square inch you'll get out of it. Tamping is hard work. Do a little at a time and pass it on to the next person. Remember to keep your knees bent, the tamper
Always tamp the ground before building onto it.
How deep do I make the foundation? Check with your local planning department or building contractors about foundation requirements and customs in your area. They will be able to give you information on the types of soil, how deep you'll have to go to avoid freezing, and the likelihood of earthquakes. Usually they go for overkill, but this will give you some useful information.
Scrape off the topsoil and put it on the garden area. Dig down (at the very least 6 inches) to SOLID subsoil or rock. You can tell when you get to the subsoil because it is so much harder to dig. Dig down to where you will be reasonably safe from frost heave. Pile the soil somewhere handy for making cob mixes later.
Roughly level the base of the foundation ditch.
Where the ground is sloped, you can make steps to sit the foundation on.
This will help prevent the house from sliding down the hill. You can even angle the steps slightly into the hill.
Dig out any roots near the foundation. Live ones can grow into the foundation and pry it apart. Big dead roots under the foundation will decay, leaving a hollow spot in the ground under your house.
For those of you who live where the ground freezes deeply, a substantially deeper foundation will be needed. Doing a deep rock foundation will take a lot of rock, dedication, effort, and time. If you want the look of a stone foundation, you may want to make a reinforced poured-concrete base up to ground level for your stonework to sit on. Embed the first layer of stonework into the top of the wet concrete.
You may decide to make the foundation beneath the door deeper than the rest so you can create a strong continuous foundation. (See illustration page 36.)
The gravel under the foundation is good for:
a secondary drain in case water makes it past your drainage system • minimizing frost heave damage in very cold climates •
How wide do I make the foundation? To estimate how thick your cob walls are going to be, and therefore how wide to make the foundation, see the wall building section (page 86).
Make the ditch for the foundation as wide as the foundation will be, plus enough room to work in comfortably.
Where the ground touches the foundation, the cold or heat of the earth will be transferred into the foundation and into your dwelling. Where temperatures are extreme, insulate the outside of the foundation with something that blocks the transfer of cold or heat and does not absorb water. Modern construction folk use that blue Styrofoam stuff. In the United States, it's called 'Formular'. We've yet to come up with something natural that works well as an outside foundation insulation. Even gravel might help, though. (Refer to page 55 to see where insulation goes.) If you plan to insulate the foundation, leave room for that, too.
For strength, make the base of the foundation wider than the top. You can do this by tapering the sides steeply, or by making the first couple layers underground a foot or more wider than the rest of the foundation.
How high do I make the foundation? Build your foundation at the very least 8 inches higher than ground level. Make it higher if you live where it's wet, where there's a lot of windblown rain, or if you simply love stone work. If you are making a two-story building, make the foundation at least 16 inches high. A common height for a foundation is 18 inches above ground level. You can check with the local builders to find out what they suggest in your area.
Moisture barrier between the foundation and the cob?
Mortar, concrete and earth slowly draw up moisture. One would think that the obvious solution to this would be to put something waterproof somewhere in the wall to block the moisture from the ground. Easier said than done! Wherever there is a moisture barrier and temperature differences, moisture condenses. Moisture barriers limit the ability of the wall to breathe. If moisture gets in, as it invariably does, a barrier will slow down the drying process. I haven't noticed any moisture problems in the structures we've built with stone foundations, thanks to their good drainage systems. Creating a good drainage system is the best way to keep your foundation, floor, and walls as dry as possible. Another minus to using a moisture barrier is that it can weaken the connection between the cob and the foundation. There are two schools of thought in the natural building fields on how to think about moisture barriers. Some say the breathability is vital, never use a moisture barrier. Others say they work OK on top of the foundation to keep the moisture from wicking up into the wall. The most natural type of barrier I've heard of is flat stones embedded on the top of the concrete or soil cement foundation to stop the upward flow of water from getting into the wall.
Remember to slant the stones toward the center of the wall and towards each other so the cob doesn't slide off the wall. (See illustrations on page 49.) Getting Plumbing and electric wire into the house Plumbing and electricity are pretty easy to do yourself. The library or a knowledgeable friend is all you need to get an understanding.
If there's any chance you'll want electricity and/or indoor plumbing, be sure to lay some 4 inch (or bigger) pipes through the width of the wall or foundation for the wires and the water pipes to run through.
You'll need a water intake and a drain outlet. These can be put at the bottom of the foundation (for buried wire and pipes) or through the foundation.
You can put the access pipes on top of the foundation and cob them in place. The wiring and plumbing is usually pretty ugly so you may want to put them lower in the foundation so they will be less obvious.
Any extra space between the access pipe and the plumbing pipe or electric wire can be filled later with cob or plaster.
Firewood box in the foundation Some folks put a firewood box opening through the foundation. The box can be filled from the outside so you won't have to carry firewood in through the house. Make the foundation extra deep if you want the foundation to be continuous.
Stone Foundations Stone looks the best and will still look the best a few thousand years from now, after your home has returned to the elements. The easiest foundation I've ever seen was a giant boulder with the house built right on top of it! Unless you have such a thing, you'll be gathering smaller stones as pieces for your foundation puzzle.
Ideally, you'll be able to gather stone from the site or nearby. Old quarries and along nearby road cuts are good places to scrounge rock. When you start collecting, you'll see beautiful ones all over! A 20 foot round building will require roughly 8 tons of stone. Be conscious! Remember, gathering materials impacts the environment.
Sometimes you may want to modify the shape of a stone. A steel mallet can be used to whack off unwanted protrusions. Practice helps you learn how rock breaks. Of course, each one has its own personality. You'll get a feel for it. Wear eye protection.
If rocks are not available, big broken-up concrete pieces make a good substitute. They stack easily because they usually have two parallel sides.
Sometimes construction companies will even deliver their garbage concrete to your place. If the pieces are too big to handle, whack them with a sledge hammer.
Remember to wear eye and ear protection.
If you like to vary your tasks, you can gather enough stones to start building, build for awhile, then go back and gather some more.
Gather stones that are as big as you can lift comfortably, and do it with care.
You'll need your back everyday for the rest of your life.
If you would rather leave the collecting job to someone else, cement suppliers and landscape firms often have rocks for sale by the truckload. Check to see that they're suitable for building before you buy. They will deliver them.
Suggestions for moving rocks Get one of the dumping-type wheelbarrows with two wheels for transporting the rocks. These are sometimes called gardening carts. This will save a lot of work. I
think they're wonderful. r With one of these you can simply:
When I was in Australia, I learned about the rock cradle, a clever back-saving tool for moving big rocks. They made them out of reinforcing mesh used for concrete slabs (cut to approximately 9 feet by 2 feet). This can be bent into a cradle shape by using some brute force and a piece of pipe slipped over the wire ends for leverage.
The mesh in Australia is made out of small diameter rebar and is much more heavy duty than the mesh I've been able to find in my town in Oregon. I tried making one out of the reinforcing mesh that I could get, and it wasn't up to the job. A welding friend may be able to help you create a strong enough mesh for a rock cradle. It may be possible to adapt this design and make a rock cradle out of heavy duty canvas.
A large stone can be rolled onto the cradle and one person on each side of the cradle can safely share the weight of the stone. You'll need to wear gloves so the metal doesn't chafe the skin on your hands. For bigger stones, a strong stick or crowbar can be stuck through the handles of the cradle and four or more people can carry the weight.
THE ROCK GAME
The rock game is a living room/lounge game that will teach you a lot about puzzling rocks together for your foundation. It's a very entertaining right brain game for all and a great conversation piece!! Collect special pretty rocks of different shapes, sizes and colors. Get some wedge shaped ones and some concave ones. Too many flat ones are boring. Keep your rocks for the game in a big bowl or large wooden tray. You can use a special little rock game rug to protect your floor.
You can get new rocks and throw out 'old' ones anytime as you learn which kinds of rocks stack well and which ones don't. This game will help you learn which rocks to collect for your foundation and how they fit together.
I hope you enjoy this game as much as I do!
Thanks Robbi and Ashley for teaching me this wonderful game!
Making a stone foundation Leave plenty of time! Building a foundation is a delightful puzzle. Well, that depends on what kind of person you are. As far as I can tell there are two kinds: the ones who love stone puzzles and the ones who hate them. I've noticed that some days I'm on and others I'm not, so give it more than one day to decide which kind you are.
If you fall under the second category you might choose to do some other kind of foundation, or find a friend or two who love stone puzzles.
It makes sense to spend a lot of time looking at the rocks to see what shape you need and which rock fits where, instead of using your muscle to lift and fit them together by trial and error. Take your time. Hurrying and rock work are opposite concepts.
Rocks have been around for a long time and they like to move slowly. Stonework at its best is an incredible meditation.
Some people say to wear sturdy shoes and gloves for stonework. That won't help nearly as much as keeping your soft little fingers and toes out from between a rock and a hard place. If you're working with someone else, be careful of each other's fingers and toes, or work on separate sections of the wall. Be mindful!
Remember to tamp!
The bottom is a good place for the biggest, heaviest stones. Find where they want to sit firmly and snuggle them up close to each other. Keep in mind that you are also creating the base for the next layer of stones to rest on. Remember to make the bottom of the foundation wider than the top. Moving stones around at or below
Stones have a mind of their own. They seem to know where they want to be. Don't argue with them: you will lose every time. Make sure each stone is happy by standing on it and rocking it. (Is this where the word "rocking" comes from?) If it wiggles, move it until it's secure, or use a small strong rock as a wedge to stabilize it. It is easier to stabilize a stone that is resting on three points than on four. Long stones that run the whole width of the wall every once in a while add strength. Continue along,
carefully fitting each stone into its place. Fill any empty spaces with small stones:
they help hold their big sisters in place.
Patience and practice are very useful at this point. Remember to stand up often and stretch your back by leaning backwards to re-squish the discs between the vertebrae back into a rounder shape. Drink lots of water! Too much rock work at a time is too much rock work. Take it easy. Warning! For the folks who love puzzles this can be very addictive.