Fidobe

[Merja Caryk]

Paper is principally wood cellulose, which is considered a fibrous material. Cellulose is the second most abundant material on earth after rock. It is the main component of plant cell walls, and the basic building block for many textiles and for paper. Cellulose is a natural polymer, a long chain of linked sugar molecules made by the linking of smaller molecules.

This brings us back to some of the derivatives of papercrete - fibrous concrete, padobe and fidobe. Fibrous concrete (a.k.a. fibrous cement) is fibrous material (usually paper), Portland cement and water. Padobe (paper adobe) has no Portland cement. It is a mix of paper, water, and earth with clay. Fidobe (fibrous adobe) is like padobe, but may contain other fibrous materials. Actually, classic adobe was made with clay earth and straw - so is adobe actually fidobe? I would guess so. There are no hard and fast rules, but recommendations are on the horizon.

Papercrete is mixed with Portland cement to obtain a very good R-value (2-3 per inch), an excellent sound absorption quality, to be flame/fungus retardant, and bug/rodent resistant. Since it is relatively light and more flexible than earth, rock or concrete, it is potentially an ideal material for earthquake-prone areas. It can be used in many ways -- as blocks, panels, poured in place, augured, pumped, sprayed, hurled, troweled on, used like igloo blocks to make a self-standing dome or applied over a framework to make a roof or dome. Papercrete is a very forgiving material, but like any other mixture, varying the mix, admixtures and curing procedures results in tradeoffs in its properties. For example, adding more sand or glass to the mix results in a denser, stronger, more flame retardant material, but adds weight and reduces R-value. Heavy mixes with added sand, glass, etc. increase mass and strength to a point, but reduce workability. In other words, a "light" mix with just Portland cement is easier to cut with a chain saw and drive rebar through than a mix with larger amounts of sand, clay, etc. Adding more than the minimum amount of Portland cement to the mix increases strength and resistance to abrasion, but also reduces flexibility somewhat, adds weight and may reduce R-value. So the trick is finding the best mix for the application. Making walls calls for a lighter mix than stucco. Roof panels will probably be a different mix than sub-floors.

The most common mixer in use is Mike McCain's tow mixer. See Mixers. It has a capacity of about 200 gallons (900 liters). The following is a starting formula for a 200-gallon batch of blocks. A 200-gallon batch will make 25-30 blocks in forms one foot (30 centimeters) wide x two feet (61 centimeters) long x five inches (13 centimeters) thick.. See Forms.

A starting formula is just that, a place to begin experimenting. Some people prefer "lighter" formulas without sand. If you plan to cut out windows, doors or other openings in the walls after they are erected, you will want to avoid using sand. It will dull your chainsaw blades very quickly.

But a typical starting formula for a 200-gallon batch is 160 gallons (727 liters) of water, 60 pounds (27 kilograms) of paper, 1 bag or 94 pounds (43 kilograms) of Portland cement and 15 shovelfuls or 65 pounds (29 kilograms) of sand. The sand adds thermal mass, reduces flammability and shrinkage, and packs down the slurry for a denser, stronger block. See above for caveats regarding sand.

Half a bag of Portland cement will work too, but the slurry will dry more slowly and will shrink more. The blocks won't be as hard or flame retardant when dry. Some people use two bags of Portland cement in areas where strength is most important - for blocks at the bottom of walls, roof panels, and for floors.

If you are opposed to using Portland cement, you should try some experiments with paper and clay and with other binders (see Other Binders below). There are some interesting websites on the internet, which give some fascinating insights into "paperclay." What you need for fidobe (any fibrous material and earth with clay) or padobe (paper and earth with clay) is a fibrous material or paper, and earth with high clay content. The clay content of the earth should be at least 30 percent. With regular adobe, if the clay content is too high the adobe may crack when drying, but adding paper fiber to the adobe mix strengthens the drying block and gives it some flexibility, which helps prevent cracking. The earth (with clay) to paper ratio can be varied for different applications. Since earth is different in every location, do some baseline experiments with 4-to-1 ratio - earth to paper, by weight. This is a good place to start in order to find a mix for a strong, lightweight block.

If Portland cement in small amounts is acceptable to you, you might try ratios like 6:3:1 or 7:2:1 paper, earth, cement. Basically, the more clay in the earth, the more paper you can use, but the binder should not fall under ten percent.

Before mixing the above ingredients, screen the rocks and small stones out of the earth. Again, the earth should have 30 percent clay or better. If you are wondering how you determine the amount of clay in earth, there are two easy ways. First of all, make sure you are testing earth with no organic materials in it. Usually that is found below the roots of plants and grass a foot or two underground. If you want to test a large volume of earth for clay content, make sure you a get a few handfuls from different points in the sample area and mix them together before screening. If there is any clay present, and it is the slightest bit moist, (spray some water on it if necessary) it will stick and cake up on your shovel making the shovel quite heavy. Take a handful of this damp earth and squeeze it. If it stays intact in a lump, it has some clay in it. If it can be rolled out into a "worm" without breaking up, it has more clay in it. If the worm can be draped over the edge of your hand about three inches and stay intact, it has quite a bit of clay in it.

I have seen something which makes me believe that going totally without Portland cement could be a problem - termites on the surface of a papercrete block. I was visiting a building site in New Mexico. Several hundred double fist-sized pieces of papercrete had been tossed in a pile and over a period of weeks had settled into the damp worksite soil. I began turning over pieces looking for any kind of damage. For some time I found nothing at all. Pieces embedded in damp mud for a long time were perfectly clean and intact. Then I found one, which had a small piece of unmixed paper embedded in it, which had been in contact with the damp soil for some time. The paper was not coated with Portland cement. There were a number of termites around the unprotected paper. The paper and mud scraped off very easily and I carefully examined the rest of the surface of the piece. It was completely clean. I then tried to break the piece into smaller pieces to look inside. It wouldn't break up and the small pieces that did come off left completely clean surfaces - no dirt tunnels or other evidence of termites. I believe that the uncoated piece of paper was the only thing drawing the termites. I have heard that some people put a shovelful of Borax in their mixes to discourage bugs. I have examined other buildings, five to nine years old, which I'm sure were built without Borax and they showed no obvious signs of bug attack.

Please consider a safety note on formulas. Unless you add a significant percentage of non-flammable material to any mix, both papercrete and fidobe (or padobe ) will burn. Papercrete made with a 4-to-1 ratio of cement to paper, by weight, won't burn at all, but that may be too much cement. Papercrete made with a 1-to-1 ratio of cement to paper, by weight, will smolder like charcoal, but does not burn with an open flame. Smoldering with no flame could result in unlikely but dangerous scenarios.

One practitioner is particularly sensitive to the possibility of a roof collapse should wide areas of a papercrete wall smolder for hours without detection. Another practitioner tested this possibility and thinks that such an occurrence is highly unlikely. He bored a three-inch hole in a papercrete wall and emptied an entire can of lighter fluid inside. He managed to get the papercrete to begin to smolder, but it would not continue to smolder for long because of lack of oxygen. It was suggested that fireproof mortar (high percentage of Portland cement or other fireproof binder) be used between the blocks, and fireproof stucco be used on the outside of the home to "encase" the blocks in fireproof "containers". This would limit a smoldering fire to the destruction of only one block, if it should ever occur at all.

Fidobe or padobe made with 3 parts soil to one part paper, by weight, supposedly won't burn either. Again, that may be too much soil. The intention is to be safe, but not sacrifice the qualities (R-value, light weight, strength, etc.), which make papercrete and its variations attractive to use in the first place.

There are alternatives to Portland cement, which can be used as binders, either alone or in combination with Portland cement. They include fly ash, bottom ash, rice hull ash, Plaster of Paris and lime. There may be others. Fly ash is ash left over from burning coal, which in the past was allowed to fly out of the smokestacks of power plants into the atmosphere. It is now caught in giant air filters, bagged and sold. I examined several structures built with papercrete block using fly ash and Portland cement in a 35 percent to 65 percent ratio as a binder. They were five years old and in excellent condition. Using fly ash as 35 percent of the binder cuts the Portland cement cost nearly in half and helps recycle fly ash. Bottom ash is heavier than fly ash so it sinks to the bottom of the furnace. I have heard of bottom ash being used, but have not seen papercrete made with it. Rice hull ash is burned in power plants in areas of the country where rice is grown. We currently have 100 pounds (45 kilograms) of rice hull ash on standby for tests. Test results with rice hull ash will be posted in Tests soon. Plaster of Paris is a variety of calcined gypsum. You probably have seen it in the form of drywall sheets. In powder form, it is really quite expensive, but in situations where it is necessary to join papercrete and wood, it is very effective. A small sample made with it was placed on a 2 x 6 piece of wood and was very difficult to pry off with a trowel. The papercrete seemed literally glued to the wood.

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