Cementitious foam insulation –also known as Airkrete–is a cement-based insulation product that is decades old. Despite its many advantages, the product is not widely known or used. That could be about to change.
What is Cementitious Foam Insulation?
The main ingredient of cementitious foam insulation is magnesium oxide derived from seawater–not mined limestone. Small amounts of ceramic talc, water, and a foaming agent are added during the manufacturing process. Before it hardens, Airkrete looks like–and has the consistency of–shaving cream.
Once it cures, Airkrete is a light non-structural cement that does not sag or shrink. It is an ideal insulation for walls, roofs, and wood-framed floors–such as those between suites in apartment buildings. Cementitious foam insulation does not expand–making it an excellent product for insulating existing walls without removing drywall.
The dried insulation is easy to scrape out if plumbing or electrical repairs are required. Or wires and pipes need to be moved. It comes out as a powder–not in chunks. The resulting voids can be refilled using low-expansion spray foam insulation in a can. The products will not react with each other.
Cementitious Foam Installation
This type of insulation is one of the best choices for renovation projects because it is non-expanding. It is installed by drilling small holes in the wall–interior or exterior–for hose access. The foam fills each stud, rafter, or joist cavity. It seals all gaps and cracks. It also encases electrical wires and boxes, plumbing, and ducting without leaving uninsulated pockets.
Airkrete is also installed in new construction and complete retrofits before the drywall is on. A retention fabric supplied by the installer is stapled onto the insides of the studs. Airkrete foam is then sprayed between the fabric and the exterior. It does not expand like polyurethane foam so drywall can be applied directly over it.
Cementitious foam is not as messy as polyurethane. It cleans up with water before it cures. Family members do not have to leave the house during installation. There is no harmful off-gassing and no hazardous fibers to inhale.
Why Use Cementitious Foam Insulation?
Cementitious foam insulation has many advantages over other products. Here are some very good reasons to consider using it.
- R-value. R-3.9 per inch. R-value does not degrade over time.
- Mold. Resistant to mold growth even in high-humidity locations.
- Fireproof. Does not burn or smoke. Can be used as a firestop.
- Seals. Completely fills cavities without leaving voids around obstructions. Fills gaps and holes. Seals edge to edge. Does not settle or shrink.
- Vapor Barrier. Does not require a vapor barrier.
- Pests. Insect and rodent resistant. Insects do not survive burrowing through it because it is abrasive and will kill them.
- Versatile. Can be used in walls, ceilings, and vaulted roof cavities. New construction and renovations.
- Soundproofing. Good soundproofing qualities. Quiets plumbing sounds. Can be used in interior walls of bedrooms, home theaters, and bathrooms. Best practice is to drywall one side of the wall first if new construction. Renovation installation requires holes to be drilled into each stud cavity.
- Environmentally Friendly. Cementitious foam is an inert insulation. No CFCs. No formaldehyde. No off-gassing. No Volatile Organic Compounds (VOC). No fireproofing chemicals. Recyclable. Can actually be ground up and recycled into compost or directly into gardens.
Why Not To Use Cementitious Foam Insulation
Cost and availability are the two biggest disadvantages of cementitious foam insulation. Lack of availability adds to cost.
Cost
Cementitious foam insulation costs about 20% more than closed cell spray foam insulation–approximately $3.00 per board foot. (A board foot is one square foot one inch thick.) Add to that the cost of travel if there are no installation companies nearby.
Availability
Airkrete trains, licenses, and certifies all installers that use their product. They claim to have installers in various countries worldwide and that some will travel from country to country. In many places, this could still be a problem. For instance, there is currently one installation company in Canada. Canada is only 2% smaller than all of Europe–close to 4 million square miles (about 10,000,000 square kilometers).
Availability of Airkrete in the US may begin to improve. They have partnered with Dr. Energy Saver to improve county-wide coverage. The required training and certification process may take some time to complete.
Cementitious foam DIY installation is not an option. It must be installed by Airkrete-certified installers. DIY kits are not available.
Metal Contact
There are reports of cementitious foam causing damage to steel when in continuous contact. Concrete-based material is alkaline and can speed up the corrosion of galvanized steel and aluminum.
Using alternative types of insulation on metal buildings like shops and barns will eliminate any chance of corrosion from concrete foam. Other choices include spray foam insulation, mineral wool batt insulation, cellulose loose-fill insulation, aerogel insulation, or Icynene insulation.
Shrinkage
Cementitious foam is installed in enclosed wall cavities under pressure. Slight pressure remains after the installation is complete and the product cures tight to everything inside. There is no shrinkage.
Open cavities using retention fabric cannot be blown under pressure–making a slight amount of shrinkage possible. Insulation that does not adhere to the studs can allow air penetration. New construction framing also contains moisture. As it dries out it can pull away from the insulation. Wood expands and contracts with changing temperatures and may also cause tiny gaps.
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