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Insulation and Exterior Layer

Photos are of the arched columns which were examined earlier. Hard foam insulation has been fit into the columns to make them look bulkier. The change in brightness near the top of the columns is shade beneath the eve, which is more obvious against the darker wall to the right. Careful observation of the steel bars in the columns will reveal they are the same here as shown in chapter five.

The hard foam insulation is called closed-cell because water cannot migrate through it. The kitchen window is visible at the far right, east. An adobe-like architectural mass which Frank was striving for has become evident at the right arch, near the standing roll of wire. That wire is inexpensive welded wire known as hardware cloth (1.25 centimeter squares = 1/2"). Notice that strips were cut from the roll and used where the kitchen wall ends and becomes part of the first arch.

The darker color underneath the wire mesh of the kitchen wall is called builderÕs paper. It is a type of paper treated with waterproofing material. The lighter and somewhat ragged looking material around the window is known as window flashing, another standard construction product made of paper.

Notice that the thickness of the materials match the outer line of the foundation. This design feature is also seen in the drawing on page 26, which is slightly different because that wall will be buried. The reinforcing bar protruding from the slab in chapter 2 shows this distance clearly.

One-half centimeter pencil steel (1/4") is quickly clipped with hog rings to the outer layer of welded wire to hold the insulation away from it and ensure that the armature is encased by plaster on both sides. In other words, there should be 1/2 to 5/8 cm of plaster between the steel armature and insulation (1/4 - 5/16"). The thin pencil steel bars, not shown in the graphic representation, would be clipped horizontally on the left side (imagine the grey tone inside squares on the left to be the insulation surface).

The graphic drawing below illustrates a plain wall without insulation in the view looking downward. Notice once again that there is no fine wire or metal lath in the three dimensional view where the pencil steel is clipped on to create the half centimeter of plaster between armature and insulation. If insulation is added after the total structure is built, then fine wire is need on both sides as shown in the smaller view, looking downward.

Fine wire on one side is metal lath and hardware cloth on the other. This arrangement can be multiple layers of poultry wire where metal lath and hardware cloth are unavailable.

It is easier to push plaster through larger openings but they do not hold up wet plaster as well as smaller openings. Voids are areas where cement plaster does not fully surround inner armature steel. A quality control person taps the work area with a hammer to create vibrations which cause the plaster to settle and expose voids. Too much vibration will cause plaster finish coating outside fine steel of the armature to liquefy and slump to the ground, which upsets everyone concerned.

There are two distinct planes of plaster. The rough inner plaster is left behind by using hands as a pump to palm push plaster into the armature. It is best to use hands and gloves at first. Finish plasterers follow with trowels etc. Close out each day with a vertical line from floor to ceiling exactly as illustrated and joints will be virtually invisible. Fresh plaster requires 28 days to cure perfectly, it has 98.6% of its cure time to share with the last work of yesterday and the first work of tomorrow.

The distance from the finished plane across the hand working area to bare steel is ten to 20 centimeters. Yes, mechanical application is possible, too. Insulation can be sprayed on by machine, or, placed as hard foam or treated biological fibers.

Insulation is represented by the grey plane behind the outer layer of welded wire, to the readerÕs left, in the graphic. As noted previously, 5 - 7 mm pencil steel has replaced expanded metal lath on the outside of the armature. A person on the outside pushes the hard foam insulation against the armature. Lengthwise, vertical, razor-blade cuts in the stiff foam allow it to be bent to fit the curve by the outside person, who also, simultaneously places the black paper vapor barrier.

A person on the inside passes a wire through the insulation to the outside person, at a location which makes a nice place to tie the wire when it is returned by the person on the outside. The outside person knows where to return the tie wire because the inside person gives directions; down two centimeters, etc.

Before the outside person passes the tie wire back inside; that person loops the wire through a piece of scrap welded wire, from the scrap inventory. The minimum scrap-size is two squares (about 15 x 30 cm). Thus, when the inside person pulls the wire tight and ties it, a scrap of welded wire holds the insulation and paper membrane tight against the armature (spaced outward 6 mm by the pencil steel).

The tie wire will penetrate both foam insulation and vapor barrier in a straight line 75 - 80% of the time. A 2 - 3 mm piece of welding rod can be used to prepare a hole or otherwise assist in passing the tie wire through when nothing else seems to work.

When this phase is completed, the insulation is covered with black paper and there are patches of scrap welded wire placed strategically and spaced at about 50 cm. Larger pieces of welded wire are easily clipped to the scraps and secured to the window frame steel as well. At this point one is contemplating the strength of a double membrane of ferrocement which is connected at doors, windows and roof-line.

Graduation to double-plane ferrocement engineering is not a small step. Anyone reading this far knows how to design for both beauty and strength. Congratulations!

Take a moment to remember the concepts of a hollow sailboat mast and the great strength of the welded reinforcing bar planes discussed on pages twenty and 21. (Hollow sailboat masts actually are strong enough to haul a boat through pounding seas). The square shape of the hollow pillar is also opposing planes. It has strength which can be directly experienced by bending cardboard before and after it is assembled into a box.

The exterior wall connected to the interior wall via doors, windows and ceiling is analogous to the cardboard box. Connected planes are significantly stronger than the single planes in isolation. The arched pillars are a simple version of this concept.

Window and door frames are installed prior to the insulation and outer steel. The first step is to assemble an inventory of frames made of rebar. Number three bar, about one centimeter diameter is sufficient for all but the largest of windows. Each window requires eight sharply bent right angle pieces. Four right angles of proper dimension are welded together to make a rectangle which surrounds a given window size. Two surrounding rebar frames are required for each window. The two frames are joined by stubs of #3 rebar which are long enough to make a frame thickness sufficient to include finished thickness of inner and outer ferrocement plus insulation. This calculation of thickness is larger in areas of curvature or vertical slope.

The window frame sketch shows eight corner pieces and eight connectors, which are positioned so as not to intrude into the window opening. Lay the first rectangle pieces on the ground or bench and weld them together, then do the second frame rectangle. Next stand the stubs marked with an asterisk against the still hot frame and weld them to it. Now there is a rebar rectangle laying flat with several stubs aimed upward. Tap the stubs to straight vertical with a small hammer as you weld them to the frame. Turn the frame with the stubs over and position them to the second frame and weld again. These are quick and easy frames which weld to the armature as you hack out a window hole. Tack weld an X to keep frames square while they are being handled.