This is the second of a three-part series on Usonian concrete floors. Links to the other parts are at the bottom of this page.
Starting in the mid-1930s, concrete floors were an important component of a large majority of Wright’s subsequent buildings, both residential and non-residential. In the Usonian house, its concrete slab served as the the medium through which the house’s radiant heat flowed, it was the base for installation of the wood walls of the house and it was the finished surface of the floor. Wright’s practice of making construction elements serve multiple purposes is both a manifestation of his genius and a challenge to stewards as they maintain their buildings.
It cannot be overstated that each restoration project is different. There is no one solution that fits all projects. The information given here is to provide building stewards an understanding of the original, typical process of floor installation, show examples of restoration and an give an overview of common maintenance protocols. It is hoped this information will help inform building stewards as they plan their own restoration and maintenance strategies.
Feel free to share your comments and questions about this information through the link at the bottom of the this page.
Patching and Replacement of Concrete
Conditions on each site will vary, so, as noted above, process and product information is given here to provide a start for research of each restoration project. We encourage thorough advance planning and product research, and working with experience restoration professionals. In execution, all processes and products should be tested in mock-ups or on inconspicuous areas and time should be allowed to understand its effects on the applications.
The patching or repair of a small, damaged areas of concrete or the replacement of a complete section or several sections of a floor both have their complexities. Patching requires careful matching of both the texture and color of the immediately adjacent finish. Replacement of one or more sections requires and understanding of the full process of installation of the concrete and its tinting.
Depending on the condition of the floors, the first step may be to remove layers of paint, wax or other accretions. Architect John Eifler describes this process at Laurent House:
The concrete floors looked horrible when we started. Ken Laurent had painted the concrete a variety of red colors for reasons unknown. To restore the original tinted concrete, we first cleaned the concrete using Shineline Emulsifier Plus (008404) cleaner – the same cleaning product used by the owners of the Turkel House. This enabled us to determine what segments of the floor needed to be chemically stripped. Using a soy-based stripping product, we removed the paint on the various parts of the floors, one square at a time.
Tarantino Studio has provided specifications for the repair, restoration and maintenance of the floors at the Hanna House. For initial cleaning Tarantino specified Prosoco products: Graffiti Wipe to remove colored coatings; Fast Acting Stripper, to remove sealer and residue; Degreaser in the kitchen and Safety Klean, to provide porosity to the concrete.
The need to patch small areas is the most common problem presented to stewards of Wright’s concrete floors. Over the course of decades, many of these floors have seen their share of damage. Among the most common types of damage are:
- Physical damage to the concrete, such as divots from carpet nails and unsuccessful past repairs
- The application of inappropriate finishes, such as paints or other materials, such as glue for carpets
- Wear, including wear from heavy traffic, as well as stains
At Hanna House Tarantino Architects specified:
- For damaged areas at the Hanna House, specified Portland cement for small areas and Patchcrete for larger areas
- Tinting was done using Scofield (Sika) products
- Sealing was done with Scofield (Sika) Selectseal Matte
At the Laurent House, after the cleaning described above, John Eifler recommended, “two applications of Kemiko tinted red wax were applied to make the color more consistent and to act as the ‘sacrificial’ wearing surface for the floor.”
Joanne Kohn, former chair of the board of the Frank Lloyd House in Ebsworth Park (Kraus House), described the application of the Kemico wax, Stone Tone Wax – English Red, at the Kraus House:
The wax comes in gallon cans and has a thick liquid consistency. Four people participated in the waxing process. While the house has 1900 square feet, the floor under the beds, which went down to the floors, was not treated. A painter’s stick was dipped into the can and thinly dripped onto a section of the floor….the waxing was done in SECTIONS. Cloths were then used to spread the wax evenly, BUT NOT HEAVILY, over the floors, into the corners and into the crevices of the geometric forms of the floor.
The wax was allowed to dry within a matter of minutes. When it was totally dry, the restoration contractor used a hand held electric buffer to go over the newly waxed area. The process continued: removing of furniture, cleaning of floors, hand waxing and buffing, until the entire floor was complete. It was a day’s work. One gallon of wax was used.
One of the reasons that project-specific research is so important is because products can be discontinued or the manufacturer/brand can change. This was discussed above in regard to the A.C.Horn Colorundum. The Kemiko red wax is no longer available. In 2013, Joanne Kohn coordinated, with the Building Conservancy, the bulk purchase of the wax by a group of building stewards. The wax has not been available since then.
At the Gordon House, the building’s 2001 reconstruction required the creation of a new slab. By 2012, the recreated slab had deteriorated significantly and Prosoco products were used to refinish it. Here is a link to an article that gives a good overview of the process, where Prosoco ColorHard was used to re-created the tinting of the floor slab after the house was reconstructed in Silverton, Oregon.
The decision to replace single or multiple sections of a concrete floor is never taken lightly by a building steward. While patching can be a complex and painstaking effort, larger scale restoration is a much heavier lift. It is a dirty project that is much more disruptive to living patterns than a small-scale patching effort. If you are contemplating a large-scale slab replacement, we strongly recommend consulting a restoration professional who is experienced in this area. The information provided here is intended to help give an understanding of the issues you may face. Reasons for replacement include:
- Failure of all or a portion of a radiant heating system (again, see Radiant Heating 101)
- Serious concrete failure
One advantage to complete restoration of a section or sections of a concrete floor is that the score lines of Wright’s design module can provide a clear boundary for the transition from new to existing concrete. Unlike partial patching, where the slightest difference between the color and texture of the patch will show up against existing concrete, the score line can allow for a slight variation, without the variation being immediately noticeable. That being said, matching to existing conditions is still critical.
Whenever making significant interventions into a building designed by Frank Lloyd Wright, it is important to remember that elements can interlock in unexpected ways. As noted above, this is in no small part a function of Wright aim to make single building elements serve multiple purposes. In the case of a Usonian slab, the slab may or may not hold up the walls. In the Usonians, masonry walls were typically constructed before the slab was poured, but wood walls were usually constructed (or installed) on top of the slab, using the module lines as guides.
It is important to have as full an understanding as possible of the the ways in which a house was constructed in advance of any major restoration work, especially one as basic as work on a floor slab.
Richardson House Case Study
Restoration of the Richardson House slab by Tarantino Studio restoration for Edith and John Payne, who bought the house in 1996, is one of the most extensive and successful of the slab restorations. The primary motivation for the replacement was the installation of a new radiant heating system.
Lawrence Tarantino’s description of the process in the Building Conservancy’s Summer 2008 Bulletin is worth quoting at length, both for its information and as an example of the importance of thorough advance project planning:
The consequences of [the Paynes’s] decision were more far reaching than they could have imaged.
After careful research, a strategic plan was developed and a project methodology and implementation established. The work began with detailed photographic documentation of the furnished interior. This became an historic record and a valuable reference during the reconstruction phase. the survey also included careful measurements of the entire house to produce as-built drawings of the conditions that existed before dismantlement began. The original drawings proved to be another priceless resource and evidence of the architect’s design intent….
The architect’s role as project manger provided additional benefits. During the document preparation phase, a team of specialized contractors appropriate for the type, size and scope of the project were interviewed an their ideas and concerns were reflected in the contract documents. The construction documents’ accurate anticipation of the unknown conditions reduced the risk of unforeseen costs during the project….
Following a period of separation anxiety, the owners cleared out an the carpenter began the meticulous task of removing all the built-ins. Each piece removed was photographed and labeled to facilitate the reinstallation process….
Once all rooms were cleared, exposing as much of the concrete floor as possible, reference marks were placed at the base of the walls to document where the existing joints of the hexagon units intersected. These points later became the reference guides for the replacement of the hexagonal unit grid pattern.
When the house was finally empty, each room was entirely encapsulated to control dust during the saw cutting and jack hammering of the concrete. To protect the lower and most vulnerable areas from potentially inadvertent impact, rigid foam panels were placed against the cypress board and batten walls and ceilings. The remaining surfaces were covered with heavy-duty polyethylene sheets supported by ghost structures instead of direct mechanical fasteners. (Fig. 1, below)
After all the walls and ceilings were protected, the demolition and removal of the concrete floor mat began.
Once the systems of the house were carefully analyzed, a plan was devised for removing the concrete floor from under the house. To do so, specific hexagonal floor units were retained and/or screw jacks installed to support the loads during the demolition work. (Figs. 2 and 3)
The hexagonal units to be preserved were identified and labeled and the units were separated from adjacent areas to be removed by saw cutting through the joint around them. It was then time to begin jack hammering the entire floor into pieces small enough to be hand carried in buckets to the recycling container.
Both layers of the concrete mat were found to be completely unreinforced. While this may have been partially responsible for the demise of the radiant heating system, it certainly made the removal process easier.
The absence of reinforcing also explained the presence of multiple parallel cracks in some surfaces. These occurred directly over the heating pipes as the floor settled. (Fig. 4) Other major cracks originate from the expansion joints in the base slab. These expansion joints ran straight across the house, not following the joints of the hexagons above in the top slab, allowing the cracks to transfer up through the surface, splitting hexagons in half along these lines. In total, six to eight inches of concrete material throughout the house, including all the radiant pipes was removed. (Fig. 5)
It should be point out that in the case of the Richardson House, the most severely deteriorated heating pipes were located near other domestic plumbing water lines of copper. It was in these locations that water leaks and/or condensation spread through porous concrete and corroded the outer walls of the adjacent pips. (Fig. 6)…
Tarantino notes that, as discussed above, many concrete installation were done in two layers, with the Colorundum shaken on to the upper layer. He continues,
Colorundum, intended primarily for commercial use, was commonly used in public buildings and movie houses, and therefore normally handled by an experienced (trade specific) contractor with a large crew.
The application of the Colorundum for a small house by a small contractor with a scored surface, posed many small complex issues difficult to accomplish without prior experience with this product.
the deviation from Wright’s plans was dictated by this logistical complexity. the only way the building could manage the application of Colorundum with limited manpower was to control the task in smaller phases, using less material at a time….
In the case of the Richardson House, to solve the problems inherent in the old systems, the technique of two pours was decided on to accomplish the logistical issues with the colored concrete and the hexagon scoring. But this time, instead of metal pipes at the bottom of the concrete mass, the selected replacement radiant heating system used one-half inch tubing (WIRSBO PEX Tubing by Uponor), a non-metallic product that could be placed in the concrete closer together ad closer to the surface.
Locating the tubing at the top of the base slab instead of the bottom positioned it just one and one-half inches below the surface and brought it much closer to the surface than the original installation, for higher efficiency and quicker response.
After the stone base and insulation were in place, the tubing lines were tied to the top of the concrete reinforcing mesh with zip ties and the combined/connected components were positioned so they would set in the top surface of the base slab (first pour). This placed the reinforcing, a well as the tubing, exactly one and one-half inches below the finished floor surface, resolving the deficiencies of the original system. (Fig 8)…
To recreate all the hexagon units once again, the surface of the base slab was used as a sketch pad, to lay out the complex geometry of the hexagon unit grid joints. This was accomplished by snapping lines at 60 degree angles, intersecting at the guide marks, which had been transcribed to the walls prior to demolition. Next, two-by-fours laid flat provided the one and one-half inch thickness needed for the top slab. They were set along the guidelines, forming side edges of multiple hexagons at a time. The top slab was poured in small areas at a time, reusing the forms each time. (fig 9)
Originally the entire concrete mat was poured before the walls were erected. Since walls already existed, special jointer tools were custom-made to score the 60 degree angle joints right up to the walls to create the hexagon shapes. These tools produced a deeper groove, making each joint a contraction joint to control potential cracking. Pea gravel was specified for the top slab to facilitate the use of these tools. The substitute for Colorundum was “Lithochrome Color Hardener” by Scofield [see product discussion above]. It was essentially the same product. This shake-on color pigment was broadcast onto the fresh concrete at the prescribed time, and then worked into the surface by trowel before the unit joints were tooled. This time-consuming approach required an experienced crew to work on small sections at a time in various parts of the house (Fig. 10)
In place of the standard thick rigid foam insulation, the specifications called for a thinner and more effective product know as Insul-tarp, which also acts as a vapor barrier. The original floor lacked any form of insulation or vapor barrier.
Before the concrete was sealed, another Scofield product, Lithocrhome Tintura Stain, was applied by hand. The application of this concrete stain product was executed with a method developed exclusively for the Hanna House at Stanford University in Palo Alto, California. The technique blends and unifies the new concrete flatwork with the old to create a natural contiguous overall appearance. The last step was to finish the surface with two coats of a non-slip, matte sealer. (Figs 11 and 12)
While the Building Conservancy encourages the restoration of floors to their original condition, as specified and constructed (with the understanding that as-built conditions can differ from the specifications), where the concrete floor has sustained severe damage, several building stewards have understandably chosen alternatives to complete restoration. It might be said that these are interpretations of Wright’s process, which, while not complete restoration, bring the floors closer to the original design intent.
As is described in this article on the Euchtman House, the slab there had been removed and a new slab was poured and covered with blue ceramic tile. While the tile was perfectly nice, it was in no way similar to the original red concrete floor. The current owners removed the tile, which left a relatively small amount of clearance for to restore the slab. A thin coat of red concrete was poured over the slab and the indentation of the design-module lines were recreated using a thin cord stretched over the partially cured skim-coat of concrete. The color for the floor was developed with Tarantino Architects.
At the Christie House, the owners were faced with a a severely damaged and painted floor. They decided that their best option was to recoat the floor with an epoxy finish. This process proved a challenge at the design-module grooves, where the natural tendency of the epoxy was to level the floor surface, obliterating the module lines. The owner worked closely with the contractor to ensure that this did not happen. While the new floor does not have the variation in tone that an original shaken-on concrete tinting has, the owners or very pleased with the improvement over the previous floor condition.
The Tonkens House floors had been covered with wall-to-wall carpeting. Evidence of nailing strips are visible throughout the house. Also there are areas of concrete failure. In addition, when the carpeting was installed, door undercuts were raised, so that now there is relatively large gap between the door bottoms and the floor. The owner discussed options for the floor with the Building Conservancy’s Architectural Advisory Committee. One option that is being seriously considered is installing a finished floor of terrazzo, colored to approximate the color of the original concrete. This would work well with the depth of the gap between the existing floor and the door. Divider strips for the terrazzo would follow the house’s design module. And there is precedent for using terrazzo. Wright used it in the 1954-57 addition to the Reisley House.
In his article, “Restoration and Renovation at the Lovness Estate,” owner Ted Muntz describes the replacement of the floor slab at the Lovness Studio:
TK Products Bright Kure & Seal, a 100% blend of methyl/methacrylate acrylic polymer, made here in the Minneapolis area, was applied to the concrete. Our concrete contractor had initially experimented with a syloxane dye per the architect’s specifications, but could not control the color result, so we switched to the Kure & Seal. The color came from PPG’s “FLW Natural Organic Colors.” PPG 1302 (Fallingwater) was chosen. When cured, Betco “Hard as Nails” Floor Finish was applied to the surface and a varied amount of H&C Sharkgrip was mixed into the sealer to make the surface slip-resistant.
Please Note: Each restoration/maintenance/repair situation involving a Wright building requires analysis and research to identify the correct approach. The Conservancy is sharing the information so it may be of use to others as they evaluate their own specific situation and may consider these and other approaches. The Conservancy strongly recommends that owners consult with a design professional and an experienced contractor to determine which method is best for their specific projects.
Further, the provision of this information or mention of a specific product or products does not constitute endorsement, recommendation, preference or approval by the Conservancy.
Usonian Concrete Floors 101 - Part 1 Background and Original Installation
Usonian Concrete Floors 101 - Part 3 Maintenance
Posted February 8, 2024