Concrete 101
As we continue to highlight our self-performance, we’re shining a spotlight on Dovetail Concrete, our in-house concrete team. In 2017, Dovetail established our own concrete division, bringing internally a team of experts with whom we had been working for many years. By integrating concrete into our building process, from planning through framing, we are better able to control and coordinate this important scope of work.
Detail of architectural board formed concrete with heavy “icing” between the boards
What is Concrete?
Concrete is a mixture of three basic components: water, aggregate (gravel, rock, sand) and cement (a binder made of limestone). Cement reacts with the water and adheres materials together, producing a durable stone-like substance used throughout the world. While various admixtures can be integrated to reduce the time it takes for concrete to set, increase the strength of the end product, and decrease the overall weight, concrete has not changed much throughout history.
Ancient Concrete
As early as 6500 BCE, we have used concrete and cement in familiar ways. From southern Syria to northern Jordan, the Nabateans used hydraulic lime as mortar to construct rubble masonry houses, floors, and underground waterproof cisterns. Additionally, limestone can be found throughout much of Central Mexico and both the Aztec and Mayan empires used kilns to reduce limestone to cement. Cement was used as mortar to join blocks of limestone and later thinned to cover interior walls in stucco, which were painted in hieroglyphics and murals.
Concrete in Mexico
The majority of Dovetail’s concrete artisans relocated from Oaxaca to Seattle many years ago. In an attempt to understand why the use of concrete and talented concrete artisans are so prevalent in Mexico, we dug down a bit further. Mexico continues to be the largest producer of cement in the world, and the popularity of concrete as a durable, practical, and decorative material is evident throughout the country. We spoke with Robert Hutchison, a local architect and founding Program Director for the Architecture in Mexico Studios at the University of Washington, about how the use of concrete differs between Mexico and the United States. Hutchison explained that when discussing architectural space, two words come up in academic circles - tectonic and stereometric.
Stereometric (Photos below, by Rafael Gamo) is a way of working with mass to sculpt the earth either by carving away or casting and produces a structure that appears uniform. Examples of pre-colonial stereometric construction can be found throughout Central and South America (seen above), and the southwestern US. Stereometric sensibilities can still be seen in contemporary Mexican architecture, such as these two houses near Mexico City, designed by Javier Sanchez Arquitectura (left) and Fernanda Canales / Claudia Rodríguez (right).
Tectonic (Photos below, by Fred Housel) is the assemblage of individual pieces to create a whole where the individual pieces can still be seen in the end product, and often utilizes wood and steel to do so. Tectonic expressions in architecture can be seen throughout the US, which is the largest producer and consumer of lumber in the world. Mexico's access to wood is limited in comparison to the US, so a tectonic language of building is not prevalent throughout the country. Below is a cabin in the Pacific Northwest that uses lumber in a tectonic expression. It was designed by David Miller and Robert Hutchison during Hutchison’s time at The Miller Hull Partnership.
It’s impossible to investigate differences between concrete in Mexico and the United States without addressing the relationship between the cost of labor and the cost of materials in these two places. Mexico operates with a large labor force that receive lower wages than those in the U.S. which, for better or worse, allows for more experimentation and artistry in their construction. Hutchison recounts his experience building a house in Mexico where Simpson/CJT hangers were specified, which is the least expensive way to create a blind connection at approximately $20 per connector. Instead, the local builder chose a more labor intensive route of welding custom connectors at $3 a piece. In Mexico, material costs drive construction costs, while in the U.S. construction costs are driven by labor, and concrete is a labor intensive building process. Dovetail’s concrete artisans honed their skills in Mexico, and bring with them expertise and experimentation.
Dovetail Concrete
We sat down with a team of Dovetail builders to learn about the concrete process from start to finish. Below is just a snippet of our conversations with Jason Heide (Concrete Superintendent), Chris Mega (Framing Superintendent), Chad Rollins (Principal) and Paul Caton (Project Manager).
The Importance of a Precise Pour
Following our concrete work, our framing team arrives on site and the quality of the finished concrete directly impacts the ease or difficulty of the framers job. Our concrete team feels satisfied with their work when they hear the framing team say “this is the best wall we’ve ever framed.” Echoing these sentiments, framing superintendent Chris Mega says “the concrete team is super talented, very exacting both on grid and in elevation, and they work to achieve 1/16-1/32” tolerance.” He recounts an experience setting floor to ceiling windows and sliding glass doors on a finished concrete floor slab. “We don’t have a shim that exceeds ⅛” for over 140’ of glazing.”
On one project where the concrete was poured by a different subcontractor, the framing team had to “scab” materials on top of the concrete wall to pour a “lift.” This creates a clean datum on which to build. Irregularities in a concrete pour can have a cascading negative effect on other scopes down the line and the Dovetail Concrete team strives to set up a project for success.
Architectural vs Structural Concrete: What’s the Difference?
Not much, actually! Similar to structural steel, structural concrete is often covered up. Structural concrete has the potential to be integrated into the design, exposed, and expressed, elevating the material to architectural concrete. For example, concrete ties are an essential structural component during the concrete pour. A concrete tie uses the concrete’s weight to exert equal and opposite forces on each form panel. As it pulls on one form panel, it pushes on the other, and vice versa. Designing the placement of these ties and elevating the tie material leads to a more attractive finished product. The difference between architectural and structural concrete is the quality of the finished surface because architectural concrete is visible.
To produce architectural concrete, we control the casting process a number of ways. A sealed tight form system produces crisp edges and minimizes “cream leakage,” new formwork material ensures a clean face, intentionally placed joints and ties contribute to design clarity, form liners can introduce texture, and test pours ensure the desired color and finish.
Environmental Impact
It’s well known in the construction industry that concrete has a significant carbon footprint. Local partners Sellen, Sound Transit, KPFF, and concrete suppliers are working together to develop a more sustainable concrete mix for the future. A report by them states that “1 pound of carbon dioxide is released with every pound of cement made, accounting for 5% or more of global greenhouse gasses.” Reducing cement in a concrete mix and replacing a percentage of it with slag (a byproduct of steel manufacturing) or fly ash (a byproduct of burning coal) can reduce greenhouse gasses.
Credit: Sellen, Greener Concrete 2014
Additionally, the weight of concrete can and should be used as an advantage. Concrete, while heavy and difficult to pump and place, has thermal mass which can aid in energy efficient heating and cooling. Concrete slabs pair well with hydronic radiant heat systems. The City Cabin residence (seen above) built with Olson Kundig has an insulated concrete slab with radiant tubing throughout, which allows the home to reach their Net Zero goals.
Warmboad Radiant Flooring can be installed beneath concrete slabs to take advantage of the thermal mass of concrete.
Why is Concrete Important?
Concrete is the first scope we build in a new residential project. The amount of care, craft, and attention in its construction affects and influences the entire building process to follow. Concrete is the foundation on which we build and it takes talented hands, minds, and artisans to produce it.