Aidomes.com - Domes from American Ingenuity

 Most Commonly Asked Concrete Questions 

and Their Answers

 Q: What makes your panel concrete so crack resistant?

A: The panel concrete is a special formulation containing synthetic fibers and liquid admixtures. These ingredients improve the concrete’s characteristics, create super toughness, extend durability, make concrete impervious to water, give higher tensile and compressive strength, provide elasticity for expansion, and improve freeze protection. The concrete in your dome out performs other exteriors because of its specially developed formula. Because of its exceptional composition, it actually gains strength over the years. The exterior panel concrete adheres directly to the steel mesh and the E.P.S. insulation without the need of a bonding agent.

Q: I understand when I mix concrete on site to fill the panel seams, the recipe includes the same liquid admixtures and fibers that American Ingenuity used in the panel concrete. Is this true?

A: Yes, Ai ships the same liquid admixtures and synthetic fibers with the Building Kit so that the seam concrete you mix on site will have the same properties as the panel concrete that was applied at the Ai plant.  Fibers in concrete work to reduce the formation of shrinkage cracks in concrete’s plastic state while helping to improve shatter resistance and reduce water migration. The result: tougher concrete.

The liquid admixtures you receive with your dome kit are marked A and B.  One is an air entrainment and the other is a water reducer.

The Concrete Mix recipe includes water, 1 bag Portland (type 1 or 111), Admixture A, Admixture B, ¼ large bag fibers, Sand (any sand normally used in either concrete or masonry). The Assembly Manual includes the precise amounts for each of these items.  During the assembly of the dome kit, the seam areas between the panels are filled with the fiber concrete in two applications.  In between the two applications you or your workers apply the bonding agent that is shipped with your kit onto the first coat of concrete and onto the bonding ledge of each panel before the second coat of concrete is applied. Prior to the second layer of concrete being applied, you have decided if you want the seam appearance to be flat or curved.  The second layer is sponged so that its appearance is a "sponged sand finish" to match the sand finish which is the finish on Ai's prefabricated component panels.

Q: After all the seams between the component panels and building options are concreted, what is used to seal the concrete?

A: Although most of the concrete joints will not leak, Ai does not depend on the concrete to make the dome watertight. The dome gets additional sealing with a concrete primer and two coats of good quality latex house paint that you purchase locally.  Any porous area that water will penetrate; paint will also soak into and seal. If a leak persists you can resort to an elastomeric paint in that area or in the very worst case, a stretch cloth and elastomeric paint.

Q: I am considering applying elastomeric paint over the entire dome, should I do this?

A: No. There are acrylic paints that have a considerable capability of stretching. They are very useful in sealing the outside of the dome where thermal expansion is most likely (for example where a link connects to the dome). Most all paints will stop liquid water if there are no holes or cracks, but water vapor (evaporated water) is a gas which will pass fairly easily through most Latex paints.

Elastomeric paints restrict the amount of water vapor which will pass through them. This can be a disadvantage if there is a lot of water vapor confined inside the dome. In northern domes, you can install a Heat Recovery Ventilator to remove moisture.  To read about this click on HRV. The water vapor will slowly pass through the E.P.S. and go through the concrete and practically come to a stop at the elastomeric paint. In extreme conditions the paint will bubble or blister and be filled with water which condensed from the original vapor. The blister is popped to release the water. It is difficult to repair the blistered area and make the surface match the rest of the dome.

Q: What if I get a leak in the dome shell?

A: Please call us and ask our advice. Generally it is easier to repair a leak in our concrete dome than it is to make a repair in a shingled roof. Usually caulking or painting is all it takes to seal the dome but stopping a leak in shingles usually requires removing the shingles and starting over. Use a urethane or latex caulk NOT a silicone caulk. 

Q: Where am I most likely to get a leak?

A: Two domes are connected by a passageway that Ai calls a link. A leak most likely will occur where the long flat roof of the link butts up to the curved surface of the dome shell. The expansion and the contraction associated with temperature changes produces the flex or separation at the link. The fall is the most likely problem time. We have tried expansion joints but they are not trouble free either.

You seal that area by using spandex cloth and elastomeric paint. The fabric can be bought from Home Depot or Lowes.  First apply a layer of elastomeric paint in the edge where the link and dome meet, lay a 12" wide strip of spandex cloth (whatever length is appropriate) in the paint, press the spandex down into the paint. Apply two coats of elastomeric paint, letting the paint dry between coats. 

Q: Explain why the use of a bonding agent helps prevent leaks.

A: Technology has developed now to prevent cold joints. The Assembly Manual that comes with the American Ingenuity Dome Kit explains how to utilize bonding agent and other techniques to join the concrete in the seams. Concrete, or a cement mixture, will not bond to a dry absorbent surface such as dry concrete. The reason is easy to understand when you examine the curing process of cement. When new concrete is applied over old, dry concrete, the moisture from the new concrete will be absorbed by the dry concrete especially at the surface where they meet. When the new concrete is robbed of its moisture at the joining surface it will not cure properly and therefore will not bond.

Bonding agents are designed to improve the adhesion between layers of concrete by acting as a glue and coating and sealing the dry concrete to prevent it from robbing the moisture. The bonding agent that is provided with your kit, when mixed with concrete, also increases its strength.

Q: What else do I do during the seam concreting to assure that the second layer of concrete bonds to the concrete of the panels and to the first layer of the seam concrete?

A: This is discussed in detail in the Assembly Manual, but basically you wet the adjacent panels with water and allow them to soak up all the water they will. Plus you apply bonding agent on the concrete ledge at the edge of the panel and on any concrete that has been placed in the seam.

Q: What other special features are designed into the panels of your kit to improve the bond and strength of your dome?

A: The preconcreted panels have a ledge molded into the edge of the concrete where the seam concrete is most needed to bond. This ledge increases the bonding surface, thereby increasing the ultimate strength of the joint. The steel mesh which extends from the old concrete to the new concrete is a small mesh which compliments the effect of the fibers in securing the joint.

Q: Can I spray concrete into the seams instead of hand applying it?

A: No. Ai does not recommend pumping or spraying the concrete into the dome seams because the equipment usually pumps faster than the seams can be finished. The overspray gets on the panels and unless it is washed off ASAP it will harden and be very difficult to remove.

Q: Why is it more beneficial to have preconcreted panels instead of spraying concrete all over the dome on site?

A: A continuous sprayed concrete structure will cause the concrete to cure all at once.  Preconcreted panels allow for the panel concrete to cure prior to the seam concrete being applied.

In 1976 American Ingenuity manufactured and then built its first geodesic dome prototype by utilizing reinforced concrete over E.P.S. insulation. Steel mesh was hand tied onto the propped up E.P.S. insulation, concrete was then gunited and troweled over the propped up E.P.S. insulation. Countless designs and manufacturing construction techniques were analyzed in the early years as American Ingenuity developed a new generation in dome housing. Ai has outgrown two previous models as we progressed to a six dome complex.

Ai does not recommend sprayed concrete structures because spraying concrete causes a waste of labor and concrete. The concrete ends up being 2" thick in one place and 3" to 4" thick in other places. The concrete on the dome needs to be thick only in the seams and thin on the panels.  It is a waste of labor because it is difficult for the concrete finishers to stand in the concrete and try to finish the concrete as it cures.

Q: What is the curing time for the seam concrete?

A: The weather and the mix of the concrete (amount of water, etc) will effect the curing time of the concrete. Usually by the time you place a complete row of panels and are ready to start the next row, the concrete has cured enough. If you place a panel above another panel and cracks start to form in the first coat of concrete, then the concrete has not cured enough. You have to stop placing panels until the concrete has cured more.

To apply concrete in the seams the outdoor temperature should be above freezing, preferably at least 40 degrees. The concrete cannot freeze for two days after its application.