Is glass fiber reinforced concrete (GFRC) considered eco-friendly?
I live in southern California. I'm considering using GFRC for a fireplace mantel and surround. Is GFRC a green material? And in terms of indoor air quality, is it a relatively safe material to use in a home?
GFRC, or glass fiber reinforced concrete, is a formula used in pre-cast (as opposed to cast-in-place) decorative concrete.
- GFRC is typically comprised of Portland cement, #30 silica, a pozzolan, water, a polymer, and a decorative pigment.
- The finished product is then sealed.
- The inclusion of a pozzolan increases the strength of the end product, which effectively reduces the quantity of Portland cement required; this also allows the product to be produced in thinner “slabs,” adding to its decorative qualities.
Portland cement is an energy-intensive material; therefore, the lower required cement content of GFRC makes it an environmentally preferable material over wet-cast concrete products.
GFRC does not require mined aggregate for its strength, unlike many cast-in-place applications. However, some people choose to use aggregate for decorative purposes in GFRC.
Fly ash is a potential GFRC ingredient
Some fabricators use fly ash as the pozzolan for their GFRC, but this is less common than, say, Micron HS -- a recycled glass that is ground down to a particle no bigger than three microns.
Fly ash has received a lot of negative press in the past year, some of it justified due to the potential for leaching heavy metals, so ask your fabricator what type of pozzolan they use.
Polymers mostly offgas at the shop during fabrication
The polymers used in the fabrication of GFRC are typically water-based acrylics, but this does not necessarily mean they are low-VOC.
However, the GFRC products are typically cured in the fabrication shop where most, if not all, of the offgassing will occur.
The pigments used to color the concrete are typically an iron oxide base. So there is extraction mining associated with the pigments, but the quantity used is small. Alternatively, there are topical stains and dyes that are soy or water based.
Lastly, the product is sealed with either a penetrating sealer or a topical sealer.
- Sealers are either water based or solvent based.
- Ask your fabricator what type of sealer they use and even if it is a water based sealer, ask for a copy of the manufacturer's Material Safety Data Sheet (MSDS) to determine the VOC level.
- A topical sealer can continue to offgas after installation.
My personal experience
As the owner of a beautiful GFRC bathroom vanity top, I can say with confidence that you will enjoy your fireplace surround for many years to come.
To keep it looking great, do not allow colored candle wax to drip onto the mantle, and if people are likely to gather round the fireplace, make sure you have coasters on the mantle to set cold beverages or wine glasses on.
I would like to acknowledge the contribution of national decorative concrete consultant Tommy T. Cook to this Green Home Guide post.
You can see Tommy’s work at www.tommytcook.com.
For more information:
Read "For LEED ratings, what is the best fireplace?" a Q&A answered by Sergio Grado.