The Monolithic EcoShell I and EcoShell II

by Freda Parker
October 26, 2007

Simply defined, an EcoShell is a concrete, thin-shell dome whose construction process includes a relatively new technique called Airforming. This technique uses an Airform that's made of a high-strength, high-tech fabric. When inflated, the Airform, looking like a semi-rigid balloon, creates the EcoShell's dome shape.

Monolithic has developed two types of EcoShells: the EcoShell I and the EcoShell II. They are nearly identical for end use. But each has its own construction process.

For an EcoShell I, concrete is layered onto the exterior of the inflated Airform.

For an EcoShell II, concrete is layered onto the interior of the inflated Airform.

They do, however, have this in common: The Airforms used in the construction of both the EcoShell I and the EcoShell II are removable and reusable. With proper care, an EcoShell Airfom can be used 100 or more times. That feature significantly lessens construction costs for projects involving the construction of more than one structure.

And here's another commonality: Neither EcoShell I nor EcoShell II is insulated in the way Monolithic Domes are. But both are super-strong structures that can withstand hurricanes, tornadoes, earthquakes, fire and termites. They can be insulated by including polystyrene beads or vermiculite or perlite into some of the concrete as it is applied. This insulation and the thermal mass of the concrete does provide some thermal protection.

Monolithic EcoShell I -- How it's used

An EcoShell has different uses. In industrialized nations, particularly those with temperate or cold climates, such as the United States, Canada and Great Britain, the uninsulated EcoShell makes an ideal garage, small warehouse, grain storage, shed or workshop. In other words, possibly with the exception of those living in Hawaii, an EcoShell is not suitable housing for most Americans.

But in the developing world, most of which has a tropical or equatorial climate, the EcoShell can provide permanent, secure, easily maintained and -- most importantly -- affordable housing.

In addition to homes, people living in those areas greatly need food storage facilities, particularly for grains. David B. South, president of Monolithic and Chairman of the recently formed, nonprofit Domes For The World Foundation, said, “Almost 50 percent of all stored food grown in developing countries is wasted because they don't have proper storage. So rice, wheat and other foods get infested by rats and vermin. A concrete, virtually impenetrable structure could prevent much of that.”

Then too, EcoShell I construction can boost the economy of a developing nation by creating jobs. Much of the construction can be done by hand, and locals can be trained to build them.

“The building process of an EcoShell I is a relatively simple and safe one,” David said. “If a mistake is made, the EcoShell I is more forgiving than are more complex structures.”

Monolithic EcoShell I -- How it's built

Monolithic has developed a booklet titled EcoShell I that illustrates and details the construction process, with sixty, captioned drawings. David said, “We already know that most workers -- even those who cannot read or speak English -- can catch on to how something must be done by studying this booklet's cartoon-like illustrations.” Some of those illustrations are reproduced in this article, at the end of this section. The booklet is available either as a download or purchase through the Monolithic Marketplace.

Construction of an EcoShell I begins with a small group of workers pouring a circular floor, to which the Airform is attached 2 inches in from the edge. The Airform is inflated with a small, high-pressure fan, such as fans used for heavy duty vacuum cleaners. After the Airform is inflated, rebar and then concrete are applied over its exterior.

The concrete can be mixed in a bucket or a fabric mixer and hand applied, or it can be mixed with commercial mixers and sprayed in place with Shotcrete equipment. This latter method obviously takes less manpower and at times produces better results. But the former method is also satisfactory and can be completed by inexperienced laborers.

Once the concrete sets, the Airform is removed.

When the EcoShell is to be used for bulk storage, the engineer must calculate the amount of side wall pressure and a corresponding increase in rebar must be added. In addition, there are several products available to add to the concrete mix that reduce cracking and increase concrete quality.

Since the EcoShell is generally not insulated, it won't be climate controlled, but its concrete does have some thermal value. And it can be covered with thatching, straw or dirt for insulation. Its roof can be coated with aluminized asphalt or a high grade exterior paint, preferably white to reflect heat. Recently we have added a layer of concrete that has polystyrene pellets, or vermiculite, or perlite added to it for insulation. Click here to see video explaining this process.

While the EcoShell I has its advantages, it also has its limitations. For example, Monolithic does not recommend building an EcoShell I with a diameter of more than 40 feet (13m). Since men are working on top of an Airform there is always a risk to them of sudden collapse.

All things considered, the EcoShell is one of construction's strongest buildings. It is virtually impervious to fire, tornadoes and earthquakes. It is especially practical in countries lacking wood and steel. Most countries have concrete and rebar on hand. In general, using the same amount of cement, aggregate and rebar, three EcoShells can be built in place of one conventional, concrete structure.

	Monolithic's UniShell is the ideal EcoShell I for housing in developing nations. It has a 20-foot diameter and 314 square feet of living space.

After everything has been removed, level the ground.

	Dig a footing trench approximately 8” x 8” (20 cm x 20 cm) on the inside of the perimeter stakes.

Continue placing clamp angles along the guideline. Fabric must be stretched along the line and kept even. Otherwise, there may not be enough fabric to go around.
	As placement continues, workers placing the clamp angles will end up inside. They will crawl out through the sleeve. Use a saw horse or other bracing device to hold the fabric off the workers.

First layer of concrete can be hand applied. Concrete can be troweled or “flipped” on with a small mason trowel. It can also be applied with a Shotcrete pump. Place only what will “stick.”

Here are some captioned illustrations showing an EcoShell I's construction using a spray gun to apply Shotcrete.

	EcoShell I starts as a steel reinforced concrete ring foundation/floor. Vertical steel bars embedded in the ring are attached to the steel reinforcing of the dome itself.
After the Airform is spread and fastened to the floor, it must be sealed to prevent air leakage.
	Using blower fans, the Airform is inflated. This creates the dome shape of the structure.
Rebar is placed, spaced per engineering. Verticals go against the Airform; horizontals go on the outside. Additional plywood frames for doors and windows can be set against the inflated Airform. Remove from inside after concrete sets. One inch of Shotcrete is applied to the exterior of the Airform, allowed to set, then re-coated to finish. (Concrete can be hand applied with a trowel.)
	Remove Airform after the concrete is set. Wire brush the rebar on the inside to remove any loose material, then spray .5 to .75 inches of concrete on the inside surface. Now that the shell is finished, hang doors, windows and vents. The EcoShell can be used as is or it may be roof-coated -- preferably white to reflect heat.

Monolithic EcoShell II -- How it's used

In the United States and other industrialized nations, an EcoShell II can serve the same purpose as an EcoShell I: It makes an ideal, durable and low maintenance garage, workshop, grain storage, small warehouse or shed.

Nevertheless, some people feel that the EcoShell II is an improvement over EcoShell I, since its construction system allows Shotcrete to be applied to the interior of the Airform. This difference does not seem like much to some; others think it makes EcoShell II's construction process more technologically sophisticated and therefore more appropriate for a nation with a developed economy.

David said, “For an EcoShell I, concrete is layered on to the exterior of an Airform; sometimes that is not easy. It all depends on the weather; if it's good, applying concrete on the exterior of the Airform and allowing it to cure usually progresses well. But it's a different story in bad weather. Then too, using a concrete gun outside means you must really watch what you are spraying. You don't want to hit the neighbor's car, bushes or pets. So we developed the EcoShell II, constructed mostly by working on the inside of the Airform. Now people have a choice.”

Monolithic EcoShell II -- How it's built

The key to the successful construction of an EcoShell II is Monoform— the right primer. It allows concrete to stick to the interior of the Airform. Because the concrete sticks to the Airform it is more difficult to get the Airform off after the concrete is set. It is a small penalty for being able to be able to more closely control the spraying of the shotcrete. It is almost impossible to hand apply the concrete to the interior of the Airform.

1. Airform is fastened to the exterior of the slab/footing in the same way as the Airform for a Monolithic Dome is fastened to its footing. Use clamp straps held in place with Tapcon concrete anchors (1/4" x 1 1/4" to 1/4" x 1 3/4").

2. Inflator fan is the same as that used in Monolithic Dome construction. For small domes use the Monolithic Puffer at a pressure of about 2 inches of water column. Monitor carefully. Increased pressure can expand the Airform and pull off or crack the concrete.

3. Inspect the Airform and seal it to the foundation. Then stabilize the pressure at 2 inches. Make sure the inside of the Airform is clean and dry.

4. Apply Monoform Primer to the Airform's interior, at a rate of about 300 square feet per gallon. It can be applied with an airless sprayer, but must be applied at least 30 minutes or more (up to a few days if it remains clean) before spraying the first layer of Shotcrete. The Monoform should be dry but sticky to touch.

5. Coat the interior of the Airform with Shotcrete, over the Monoform Primer and to a thickness of at least 1/8 inch — up to 1/4 inch (perferably 1/4 inch). This is Monolithic's standard mix with Kel-Crete and nylon fibers. Apply the second coat of concrete as soon as the first coat is ready or the next day (another 1/4" to 1/2" is about right). Concrete is ready for its second layer when it feels tough — not necessarily brittle. The time to re-coat in hot weather can be in 1 hour. In colder conditions it may require heat and curing overnight.

6. Directly after the second 1/4 to 1/2 inch of shotcrete is sprayed, insert barbed rebar hangers into the still wet concrete. Then spray over the barbed rebar hangers with the third 1/4 to 1/2 inch coat of concrete to lock them in place.

7. Place the rebar following the engineering specifications. Care should be taken to keep rebar as tight as possible to the shell concrete. The plan is to have 3/4" of concrete on the exterior of the rebar. Number three (3/8”) rebar spaced 10 inches on center both ways is always safe for small domes.

8. Spray balance of the concrete in 1/2" to 3/4" layers until desired depths are achieved. Concrete should reach at least 600 psi before the next layer is applied. As indicated in our table comparing EcoShell II to conventional concrete buildings, there are huge savings in concrete and rebar for the EcoShell.

Note: As the concrete is built up, the rebar should be kept relatively clean. This is done by proper Shotcrete techniques and/or cleaning for total embedment of the rebar.

9. Complete the EcoShell II with a 3/4" minimum cover over the rebar on the outside and 1/2" to 3/4" cover on the inside. EcoShell II should have a coating placed over its exterior surface. If the EcoShell II's exterior is not coated, it's considered unprotected concrete. Technically, there should be a concrete cover 2" over the rebar.

10. After a day or two, remove the Airform from the exterior of the EcoShell II. A coating should be considered and applied to protect the concrete from drying and to provide long term protection from leaks.

11. Removal of the Airform will be tough. If this is not so, there will be failure during the construction. The Airform must not let go of the concrete because a cave-in may ensue. Do not use a mold release; it will get you in trouble. The work of pulling the Airform is nothing compared to putting a fallen dome back together. Removal of the Airform can be done by simply pulling it up, bit by bit, around and around. Ropes can be affixed for pulling larger Airforms.

The chart that follows compares the construction requirements of an EcoShell to that of a conventional concrete structure. Please note: conventional buildings require 200% to 300% more concrete, 300% to 400% more reinforcing bar and double the labor. But ironically, it's the EcoShell that has the strength to withstand natural disasters.

Monolithic EcoShells vs. Conventional Concrete Buildings

Type

Size

Floor Area

Interior Volume

Surface Area

Concrete Needed

Rebar Needed

Dome

20' d x 11' h

314 sq. ft.

2,408 cu. ft

690 sq. ft.

8 cu. yd

1,250 lbs.

Square

18' x 18' x 8'

324 sq. ft.

2,592 cu ft.

900 sq. ft.

22.7 cu. yd

4,900 lbs.

Difference

-10 ft sq. ft.

-182 cu. ft.

-210 sq. ft.

14.7 cu. yd

-3,650 lbs.

Dome

30' d x 13' h

707 sq. ft.

5,744 cu. ft.

1,238 sq. ft.

24.1 cu. fe

2,500 lbs.

Square

24' x 30' x 8'

720 sq. ft.

5,760 cu. ft.

1,584 sq. ft.

42.7 cu. yd

9,200 lbs.

Difference

-13 sq. ft.

-16 cu. ft.

-346 sq. ft.

-18.6 cu. yd

-6,700 lbs.

Dome

40' d x 16' h

1,257 sq. ft.

12,197 cu ft

2,060 sq. ft.

30 cu. yd

4,200 lbs.

Square

24' x 52' x 8'

1,248 sq. ft.

9,984 cu. ft.

2,464 sq. ft.

68.8 cu. yd

13,300 lbs

Difference

9 sq. ft.

2,213 cu. ft.

-404 sq. ft.

-38.8 cu. yd

-9,100 lbs.

Link to Download The 2nd Edition of the EcoShell I Book

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