Last Updated: Mar 10, 2021
As building science advances, we tend to reach for the newest technology for the answers. Sometimes, that technology can combine ways old and new and needn't be toxic. Spray cork is a prime example of an innovative and proven solution to exterior building finishes, thermal insulation, and waterproofing utilizing an ancient, natural building material.
Spray cork is a paint or stucco alternative with a mixture of 80% cork granules and 20% water-based paint that comes in many color options.
Spray cork looks very similar to stucco in appearance. Its surface is textured and soft to the touch. Cork is very similar to paint in nature, only denser. It comes in as many colors as there are with any paint, and you can tint it as well.
You can use spray cork on nearly any surface that you would treat with traditional paint. You can apply spray cork directly over all types of conventional house siding.
Cork texture also creates a nice anti-slip surface, making it perfect for decks, patios, and walkways. Cork doesn't get as hot to the touch as masonry and stone, making it ideal for pool decks.
You can also use spray cork in interior wall cavities to seal air gaps as an alternative to spray foam but without building depth. Unlike closed cell spray foam, it is breathable and allows vapor to move through it, letting the wall assembly dry out. This application would be sprayed into an uninsulated wall cavity to seal gaps and air leakage points before installing insulation in the wall cavity. This application method could also protect wooden walls from mold and rot by acting as a protective sealant over the wood.
Spray cork can also be applied directly to interior walls if you like that interior finish style.
Cork is a highly renewable resource typically harvested from federally protected, Forest Stewardship Council (FSC) certified forests in Portugal. The trees' bark is harvested every nine years over its 150-250 year life span. Harvesting cork does not harm the trees. Better yet, the granules used in spray cork are typically the byproduct waste of the cork stopper industry.
Spray cork does not use any blowing agents. It is merely a mixture of 80% cork granules and 20% water-based paint applied with a paint spray gun and compressed air or electricity.
Because spray cork is 80% cork, it reduces the release of microplastics caused by paint degradation. Compare that to other elastomeric paints where the 80% cork would instead be a synthetic compound.
Cork is completely non-toxic and has no volatile organic compounds (VOCs). The water-based paint/resin mixed with the cork granules is also zero VOC.
It's no secret that cork is an excellent insulating material. Despite being sprayed at such thin thicknesses, cork offers some thermal and acoustic insulation. Its benefits far exceed a typical paint or stucco in this sense. The thermal insulation of spray cork is not measured in R-value. Instead, it is measured in thermal conductivity. Thermal conductivity is a measurement of the rate at which temperature moves through a material. Vipeq says that their cork has a thermal conductivity of 0.058. Like cork, a low number means it conducts less energy, thus acting as an effective thermal barrier.
Spray cork seals gaps and air leaks very well, and an air-tight building is a big step towards a thermally efficient building. Despite not having a specific R-value, spray cork is an innovative solution to improving thermal efficiency and reducing heating/cooling costs.
Spray cork can be applied over any properly prepared surface — stucco, steel, aluminum, wood, brick, vinyl, shingles, and more. You can use it on a wide range of surfaces.
Sediments and dust seldom stay adhered to the surface of cork, and when they do, you can wash the surface. After a decade, the finish could fade in the sun like any paint, and reapplication might be necessary.
Many spray cork products offer ten to fifteen-year warranties for exterior use. Cork Sol claims spray cork can last over 20 years and outlasts other exterior paints. Spray cork might need reapplication at different rates depending on the applied use. A deck's surface would likely need a reapplication sooner than an exterior wall.
Cork can last decades, but the acrylic paint component to the mix is the weak link. A typical exterior acrylic paint will last about ten years before needing to be repainted, so the 20-year claim seems pretty accurate.
Choosing a professional for spray cork installation is recommended, as it requires specialized equipment and knowledge to install. However, it's doable as a DIY project if you do your research and are comfortable using a spray gun to apply paints. Always follow the instructions on the product you receive.
If you tackle this yourself, don't forget to wear personal protective equipment like safety glasses, gloves, and a respirator if directed to by the manufacturer. The primers and water-based resins used for spray cork have no VOCs at all, but it's recommended to use a respirator for any product that is applied in a spray form.
The steps to applying spray cork siding are as follows:
First, look for contractors in your area who can install spray cork. An increasing number of contractors can install spray cork across North America as its popularity grows. For example, VIPEQ Canada offers complete installation. Installed, their product costs between $6 and $9 CAD per square foot.
If you are looking for a DIY option, there are a few online vendors (prices exclude shipping):
Jelinek charges $257 for a 12 kg (3.17 gallon) bucket. This price equates to $1.43 per square foot at 1mm thickness, but you might need a thicker application in some areas. They require a minimum order of 5 buckets, so you are looking at a minimum cost of $1287. For reference, each bucket covers 180 square feet at 1mm thickness.
ThermaShield sells their 18.9 kg (5 gallons) bucket for $160. They do not specify the square footage – this would depend on application thickness. Thermashield is a US-based company. They also offer contractor installation services for Texas, Arizona, and California.
Buyspraycork.com charges $199 for their 12 kg (3.17 gallon) bucket. They indicate that this is $3.60 per square foot at 2-3mm thickness, and each bucket covers 65 square feet. SprayCork is a Canadian-based company, and shipping can be expensive to parts of the US.
Spray cork has seemingly endless benefits.
Cork spray has been in Europe and South America for about 20 years but has only been in North America for five. While it's gaining popularity, you might have to search around for a local contractor who can install spray cork.
The more we educate ourselves about eco-friendly materials like cork, the better consumer choices and healthier living we will enjoy. Spray cork is a great way to upgrade any building's performance, and its applications and benefits are seemingly endless.
If you are interested in learning more about cork as a building material, check our articles on cork flooring and cork insulation.
Based in Washington State, Tom's education focuses on holistic land management that sustainably grows renewable building materials in a way that replenishes natural systems. His interest is in building systems that combine old techniques and modern science.
