Back to the Future
By Bryan Clark Green
Virginia Lime Works (VLW), located in Madison Heights, Virginia, is well-known in preservation and restoration circles for its careful development of historic lime mortars, plasters and paints. VLW knows that historic mass wall construction was strong, enduring, and well insulated, with wicking properties that allowed moisture to disperse efficiently. For years, the company has championed the use of historic lime-based materials, creating lime mortars that are chemically as close to the originals as possible, so that both historic buildings and their moisture-disbursing performance and insulating qualities can be restored.
But was there a way to apply these hard-won historic lessons to new construction? Jimmy Price thought so, and so he set out to apply historic technology to new buildings. The goal, said Price, principal of the family-owned and operated company, was to “look to our past to improve our future.”
The simple historic mass wall system, using brick, plaster, and stucco, has long proven itself to be efficient. The more recently-developed thin wall, or cavity wall, system, although designed to allow taller construction, utilizes a variety of different materials—block, rebar, grout, flexible wall ties, moisture barrier, brick, weeps, and mortar—all of which can fail. Traditionally walls were built to receive load and dissipate moisture. Today walls are merely curtains for engineered skeletons. Or, as Jimmy Price asks, when building low-rise buildings, why complicate things when we have thousands of years of proof that simple walls work?
VLW proposes a return to truly sustainable mass wall construction for buildings. The foundation is the ENVIRO-MENT block, a lime block that utilizes both the form and dimensions of the familiar concrete masonry unit (CMU). Masons are used to handling such blocks, and architects and engineers are accustomed to specifying it. VLW has adopted the “speed block” dimensions, 8”x4”x16”, to create a lighter block, easing assembly and providing more mortar joints to aid in movement for minimal or no control joints (depending on the building details) the block may be manufactured to any industry-standard dimension.
Currently, ENVIRO-MENT blocks are manufactured by a few companies in Virginia, but blocks can be produced anywhere by substituting VLW’s proprietary binder for cement. The binder works with any typical aggregate, and uses the same manufacturing standards as those used for modern concrete block.
Lime blocks cure over time through the carbonation (absorption of CO2) of the ENVIRO-MENT binder, resulting in a masonry structure with a drastically reduced carbon footprint. The construction process is a simplified version of traditional construction. Footers are poured, and ENVIRO-MENT soft lime mortar, produced by VLW using local sand as aggregate, is used to lay block. The wall is laid in a standard half-block, all-header pattern, resulting in a 16” thick wall. An insulating grout made with ENVIRO-MENT is poured course by course. Openings are created through the use of structural arches or solid pre-cast lintels. Floors are laid into block, with fire-cut chamfer floor joists. An overhanging roof is not required, but helps to protect the walls.
To finish a variety of options are available, whether it be brick, stone, or two- or three-coat lime stucco applied directly to the exterior surface of the block. The lime stucco can be left exposed or followed by two coats of lime paint. Similarly, a two- or three-coat lime plaster is applied directly to the interior block—no furring is necessary. The result is a naturally hygienic, fire- and flood-resistant building system that has an insulation value of approximately R3/inch (testing is in progress), with approximately R24+ for system— a wall that breathes without cavity, wall ties, or weeps.
No petroleum products are used and no imported products are necessary, putting local materials and masons to work. By emphasizing the neutrality of materials in the system, Price pointed out, “everything works in harmony with all other parts.” While this system is not designed for high-rise construction, four stories are readily achievable.
By looking to the past, the lessons of historic masonry construction can help us to building in a manner that is environmentally responsible, enduring, and eminently comfortable.
Bryan Clark Green, Ph.D., is an architectural historian and Director of Historic Preservation for Commonwealth Architects in Richmond.