«The Cob Builders Handbook You Can Hand-Sculpt Your Own Home Table Of Contents: Acknowledgements and Warning INTRODUCTION What is cob? Why build ...»
if you're using lime, mix up putty and let it sit at least two weeks make and analyze some plaster experiments carve and shape walls wet walls plaster (multiple layers if desired) embed tiles vertically along "wet" counters and for decoration on sills, etc.
paint walls or lime wash (optional) preserve exposed wood
FLOOR if you've put off doing drainage, do it now!
do some floor material experiments roughly level floor if you haven't already build step edges at elevation changes tamp for an earthen floor, level guide nails; lay floor; dry; lay next layer; dry; oil, and/or wax MOVE IN & BEAUTIFY create landscape elements porches outdoor walls paths trellises benches outdoor fire gardens
WINDOWS AND DOORSThe cob around the window and door openings supports the walls above.
You will need to make sure that the weight over the windows and doors is transferred to the columns of cob on the sides of these openings. The weight will then travel down through the cob and to the foundation below.
ARCHES Arches are very strong. The steeper the arch, the stronger it is. There has to be enough cob in the arch to support the weight of what's above it.
Arches can be used over plain glass or over framed windows. If you have a piece of glass in a frame that you don't want to see in the finished arch, simply bury the frame in the cob. You can arch over paned windows too. A clever way to arch over a rectangular door is to put a window on top of the door frame, and make a cob arch over the window. This is a good way to divert the weight over the door if you don't have a lintel.
To form the arch, sculpt it by hand a little bit at a time. Treat it like you do the rest of the cob. When you've finished cobbing for a while, make holes in the cob where you plan to add cob later. Let it harden enough to continue adding cob, making sure that it's remoistened and that the new cob is incorporated into the old. If you live in a dry climate, you can work on the arch first thing in the morning, let it dry awhile, and then add some more cob in the afternoon. You don't have to be too perfect - when the arch is completed, you can go back over it with your water bottle and big knife to give it a final shaping. When you do this, be careful of the glass! If you plan to plaster, remember that you will be adding the thickness of the plaster around the window.
LINTELS "Lintel" refers to the big hunk of wood that spans the top of window and door openings. Lintels are necessary to distribute the weight from above an opening to the sides of the openings. They are also sometimes called headers. Lintels are usually big hunks of milled or unmilled wood. A milled lintel can double as the top of the frame if you position it carefully.
When people cut large beams to size, they often save the off-cuts and then never find a use for them. It's surprising how easy it is to find pieces of big dimensional lumber just looking for a life.
If you have access to big hunks of metal or railroad tracks, I imagine these would make good lintels if you are short of wood.
Lintel thickness Lintels need to be made out of sturdy, sound wood - at least 4 inches thick for milled lumber, and at least 6 inches for unmilled lumber. The bigger the better. The look of really huge pieces of wood suits the massiveness of cob walls. The thickness you'll need depends on the width of the opening and the weight that will be above it.
Lintel width Because the lintel is holding up the wall over the opening, it will need to be about the same width as the wall. You can use one large piece of wood that's as wide as the wall, or several smaller pieces of wood laying next to each other to make up the width.
It's a little easier to get the cob to sit on squared milled lumber, but logs work OK and give a very ancient look to your home. If you choose to use logs for your lintels, you can fill the space between the lintel and the frame with cob.
Lintel length Lintels need to be long enough to span the opening and rest on the columns on either side of the opening. The question often asked in the natural building circles is: how much do the ends of the lintel need to extend into the cob? This depends on a few things: the strength of the lintel, the size of the opening, and the weight the lintel will be supporting. I have never experimented to the point of failure, but have been surprised to find that as little as 5 or 6 inches of lintel buried into the cob works well.
Use your own judgment and intuition.
Putting the windows and doors in the wall See pages 36-37 for important tips on putting in the doors.
102 Make the bottom of the window sill and build up the cob about 6 to 12 inches (more for a tall or heavy window) on the sides of where the window will be. This will help hold the window once you set it up there. Mix up some cob and bring it close to where you're working.
Make the bottom of the window sill. Set the glass, framed window, or window frame in, and check the plumb and level. (Plumb means in alignment with gravity, or straight up and down.) Then secure the window with cob. Check it often while the cob is still pliable to ensure that the window is in the position you want. Pushing and massaging the cob can move it unintentionally.
When you are making a cob sill for a window, check to make sure the sill is level.
Double check it by setting the level horizontally on the frame or glass, holding the window level, and stuffing cob under it to support it in the level position. When you're putting the window in the wall, make sure it is plumb too - unless, of course, you don't want it to be plumb. You can fix up the sill once the window is held in place.
Positioning the windows and doors in the width of the wall Because the walls are so thick, you need to decide where to place the windows in the thickness of the wall.
The window can be placed in the opening at an angle to the wall for an unusual look.
If the window is big enough for a window seat, you have an opportunity to make a wonderful place to sit! Cantilever the cob out into the room to form the seat. You may want to raise the bottom of the window 6 to 18 inches higher than the seat itself to create a back rest. This also protects the glass a little and gets the window up higher on the wall.
Remember that you will be tapering the walls, so you may want to make sure the top of the window or door will still be within the wall as it tapers.
You can put the window or door past the outside plane of the taper at the top and fatten the wall above the window or door like an eyebrow. This is a good way to save the day if you forget to put the window or door within the wall's taper and gives the house an adorable hobbity look.
For the windows that don't open, simply embed glass into the cob. You can even use pieces of broken glass.
Remember to put tape around the sharp edges to protect precious cobbing hands. Bury the glass into the cob at least 1/2 an inch on all sides. The cob will shrink away from the glass as it dries.
For large windows you must either sculpt an arch as the basic shape over the top of the window, or use a lintel to support the weight of the cob and possibly of the roof above the opening. You can shape the size and bottom of the window anyway you like. This is a wonderful artistic opportunity.
For small windows, (under 16 inches wide) you can be more creative with the window shape without using an arch or a lintel over the window.
Frames Windows and doors Ventilation is vital to a natural temperature control system, and fresh air is vital to people. Read the passive solar and ventilation section later in this chapter (page 114).
Openable windows or doors are a way to ventilate your home. To open and close, they will need to hinge, pivot or slide in a wooden or metal frame embedded into the cob. Making the frames is basic carpentry. Ask a carpenter friend or read a carpentry book about installing opening windows in their frames if you need help with this part.
If you are using recycled windows, it's easiest to fix them up before you put them in the wall. Sanding, painting, replacing panes, and glazing are all easier to do when the window or door is laying horizontally on saw horses. This way your house will also look fancier while you are building, when curious folk come to see what that wild person is up to!
If you set a smooth wooden, vinyl, or aluminum window frame into a cob wall, there is a small chance that it could be pushed out of the wall. If the frame has a heavy door or window swinging on it, the frame could possibly work its way loose from the wall.
To make sure the frame is well attached to the cob, add a strip of wood, 2x2 inches or thereabouts, running up and down along the sides of the frame. This is known as a keying system and will prevent the window from moving horizontally. Add 'rungs' to the strip on the frame to make it extra strong.
Use wood that is least likely to rot or get munched by termites. Find out which wood is the most long lasting in your area by asking local builders. Don't be too meticulous
Another way to secure the frame in the cob is to put old nails or screws part way into the frame and bury them into the cob.
When the cob dries, it may shrink away slightly from the frame. That's OK. The space can be filled with plaster later.
Remember to check the plumb and the level on the frame when you set it in place, and as you cob it in.
The window and door openings are places that are more vulnerable to the weather. One way to help protect the window or door and its frame from rain is to build a cob eyebrow protruding out of the wall over the opening.
Another way to shield the window or door is to build in a mini-roof by burying the 'rafters' into the cob above the opening. The sheathing and shingles for the mini-roof can be added later. -You can also keep the window drier by embedding wooden shingles or roofing tiles directly into the cob over the window.
The bottom of the window frames When visiting old Native American ruins, I noticed that the wood that was buried into earthen walls centuries ago has survived the test of time amazingly well. As long as the walls are dry, the wooden window frames should hold up for a long while.
The outside window sill The cob on the bottom of windows is a place that might get wetter than the rest of the building. You may want to protect this area by setting large flat stones, a wooden sill, or bricks into the cob, forming a sill. These can be angled slightly downwards to the outside and overhanging the wall below. It serves as a tiny roof eave making the water drip away from the wall.
If you raise the wooden window frame up off the sill on a little cob ledge or on bricks or stones, the bottom of the frame will stay drier.
What to do about possible shrinking around the windows Cob shrinks slightly as it dries. This means there is a chance that the windows could break under the shrinking pressure and weight. I have put many windows straight into the cob without doing anything for potential shrinkage and so far haven't had any problems. You may want to take the following simple measures to prevent any chance of undue stress on the windows and frames. Better safe than sorry.
108Here are a few things you can do:
Let the cob on the sides of the openings dry quite a bit before building • over the top of it. Because building with cob is a slow process, the walls or cob columns beside the windows will usually be drying as you go, doing a lot of their shrinking before you get to the top of the window. If you are having a house raising party and building quickly, the columns may be wet from the bottom of the window to the top. Stop at this point and let the cob on the sides of the window dry for at least a week or two before going over the top of it.
The taller the cob beside the window, the more it will shrink as it dries. If you have a high clay content in your cob mix, it will shrink more than a cob mix with a lot of sand and it will be more important to allow some settling space.
Be careful not to tweak the glass while you're building up the cob on the sides • of the window. While you are cobbing beside the windows, check the plumb and level often. Be aware that if you push the still wet cob near the glass you can distort the shape of the glass, making it more likely to crack as the cob dries.
Leave an air space for whatever spans the top of the window opening (a lintel • or cob arch) to settle down into as the supporting sides shrink. This will prevent the building's weight from crushing the window from above, if the cob columns shrink.
For lintels: You can leave a space between the window and the lintel. After the • building has dried, you can come back and cover any gap that's left by stuffing it with insulation and nailing some small slats or wooden molding on the inside and outside. If you've let the supporting cob dry pretty well, and your mix has a high sand content, you probably won't need a settling space. If the supporting cob is still wet, a 1/4 inch air gap should be more than enough. Use your own judgement.
For arches: To create a settling space on top of a window glass or frame, tape a sponge (carpet underlay works great) or a small bundle of straw or old clothing onto
Things to consider before putting in the windows and doors Passive solar design getting the most out of your windows Read the section on passive solar design on page 12. There are lots of books available on passive solar design. Do more research to give yourself a more in-depth understanding. The principles of solar design will have very different applications depending on the climate and latitude of your home. Check with your local building department and natural building organizations for information that's specific to your area. I will give you a very simplified version here that applies mainly to a temperate climate.