They are on every civilized continent, beautifully built ornate stone structures, architectural masterpieces, hand-carved out of quarried granite, marble, slate and quartz. Worldwide structures, representing a people’s culture, symbols of majesty and strength and in our own nation’s Capitol, representing a new nation. Each magnificent building’s ornate design is hand-hewn with an artisan’s precision and placed by skilled stone masons. From the distant past to our current modern era, the practice of building with stone continues, each structure reflective of the decade’s architecture.
Where it Began
It was in 1940s Russia where the concept of a thinner, façade type of fiber-reinforced cement was first experimented with. Building with large stones took too long and was becoming increasingly more expensive. To provide a lighter, stone-looking product with intricate design, glass fibers were introduced into cement along with acrylic polymer to make cement panels that could be attached to a building’s exterior. It was to be known as glass fiber reinforced cement. However, due to the type of glass used in the 1940’s and the high alkalinity of the cement at that time, GFRC was not stable and as a result, would not stand the test of time. It wasn’t until the 1970s in Europe, when zirconia was introduced to the glass fiber thus developing AR-glass fiber and the birth of what is today a successful GFRC industry.
For the past 50 years, the industry has undergone continual development in the products and varying ratios of those products to produce highly stable, lightweight panels capable of representing very intricate design. The main components of GFRC are high-grade Portland cement, silica sand, AR-glass fibers, water and acrylic co-polymer. A super plasticizer and color pigments are options to the mix.
Most decorative GFRC panels consist of a face coat that has no fibers and a backer coat with added glass fibers. The face coat allows for a smooth finished surface with intricate detail, with the backer coat providing stability to the structure. Some castings are poured solid with varying dimensions and thicknesses. The process is relatively straight forward but does require multiple steps and proper sequencing.
First, you need to have an original pattern. This original can be made from many different things like wood, foam shape, an actual stone, an existing statue or original carving, and so on. A two-part silicone mixture is then pored over the original, which was first coated with a release agent, to make a flexible mold; a negative of the original.
In some instances, a plastic copy can be made. This plastic copy serves as a medium that can be adjusted by adding fillers or taking out unwanted features or whatever the final design dictates. All design modifications are made to the copy allowing the manufacturer of the GFRC shape to protect the integrity of the originals.
Once the plastic copy is finalized, a reusable mold can be made. Again, a formulated two-part silicone mix is poured over the plastic mold which is contained within a framed area. All areas in the frame are coated with a release agent. This framed structure creates boundaries and allows for a minimum mold thickness. Once cured, it is peeled off and a re-usable mold is ready to go. For the solid-poured pieces that may require stacking or specific placement to create larger shapes, attachment components need to be embedded into the molds, as well.
Even though manufacturers are using a cement product, a different mindset needs to be used in the mixing of the cement products. Much like production stucco, one should always add dry to wet to avoid clumping in the mix. But unlike stucco production mixing, one absolutely must add the dry components to the wet components. Further exact weighing of all components, precise measuring of liquid additives and color products and timed mix times are all paramount to the success of the finished product. Another important must-do is to select the proper mixing tools. Because there is the addition of glass fibers and because they cannot be shredded in the mixing process, a high-sheer mixer is commonly used.
Here is an example of a proper mixing sequence:
- Weigh all material for mixing
- Add all liquids and mix thoroughly
- Add pigment (if used)
- Add sand
- Add cement and increase mixer speed
- Mix 1-2 minutes, then lower mixer speed
- Add fibers gradually until dispersed (about one minute only)
A high-performance ingredient in the GFRC mix is the Copolymer additive. This is a cement game-changer in that it eliminates the seven-day wet cure process required for cement applications. It has a plasticizing effect by making the mix workable with a low water-to-dry-product ratio (less water, more strength) while maintaining tensile strength and impact resistance. Additionally, it helps to maintain color consistency, reduce moisture absorption, efflorescence, and craze cracking typically associated with shrinkage during the curing process. If this is not enough of a cement panacea, a super plasticizer can be added in very small amounts. This magic bullet allows for even more increased workability and is typically used in spray applications.
In today’s modern construction, GFRC panels are commonly attached to a prefabricated framing structure creating an exterior panel façade. Panel sizes are determined by the material (mix) properties, the specified and engineered building requirements and the shipping restrictions. There is a cost savings in that the lightweight panel structures can have very deep sections without additional framing requirements. There is a latitude of design capabilities without the need for additional structure. This is a very desirable feature to create either a very ornate modern look, or a classic quarried and hand-hewn appearance. And then there is the savings in time. Because the GFRC panels are themselves self-supporting, they need only be flown into place with a crane where they are attached to the exterior of the building. There is no need for an experienced carver or stone mason because contractors only need to attach the panels to the building.
The flexibility of cladding a building with GFRC panels can also lend to energy efficiency. The GFRC designed skin can also be affixed to structural insulated panels. These insulated panels crate a continuous layer of insulation on the exterior of the building helping to maintain a constant interior temperature, thus lowering heating and cooling costs.
Another important advantage of GFRC is the flame resistance. The cement resists heat transference from flames and protects the building’s inboard components from exposure to fire. With a zero-smoke rating and zero-flame spread rating, GFRC panels are proven performers for today’s commercial construction Class A fire-rated projects.
Design flexibility, high strength-to-weight ratio, durability, lower cost and ease of installation highlight the characteristics of GFRC panels. In our modern and fast paced construction environment a design professional can achieve the classic appeal of a beautiful and ornate stone structure that, like their quarried stone counterparts, will stand the test of time.