Architectural polished concrete: Defending design intent

To create resilient concrete, one must keep external slab moisture/contaminants out and internal moisture in. This can only be done by controlling vapour and water transmission. The reason why there are so many common problems (like the ones illustrated here) is due to designing concrete that allows moisture to freely travel through the concrete. Images courtesy Tao Group

Durable

A floor material needs to be able to withstand wear, pressure, and damage—concrete can do all this, but only if done correctly. All floor materials will eventually show signs of wear given an extensive amount of traffic, but a hard and dense surface is essential to keeping this minimal. When the top surface of concrete is densified by way of microscopic crystallization, the upper portion of the slab becomes extremely hard and abrasion resistant. Sealers or other temporary topical finishes are very soft and will scratch and wear away quite easily.

Maintainable

To create resilient concrete, one must keep external slab moisture/contaminants out and internal moisture in. This can only be done by controlling vapour and water transmission. The reason why there are so many common problems (like the ones illustrated here) is due to designing concrete that allows moisture to freely travel through the concrete. Images courtesy Tao Group

Densification of the surface also contributes to concrete’s ability to reject dirt and liquids. Produced correctly, concrete is inherently resistant to contaminants. What stays on the surface gets easily removed from the surface. Spills that do not have a chance to get into the pores beneath the surface do not get the chance to become permanent stains.

Therefore, routine maintenance becomes much easier and more likely to occur regularly. Rather than create slabs needing constant reapplication of coatings or sealers that mitigate moisture and vapour transmission, one should design a slab that performs so the requirements for the material and labour are reduced.

Coefficient of Friction

There are still a few specifications that may require static coefficient of friction benchmarks, but the trend has increasingly become to use dynamic coefficient of friction (DCOF) benchmarks. Measuring DCOF with standards like ANSI B101.3, Test Method for Measuring Wet DCOF of Common Hard-Surface Floor Materials, or ASTM E303, Standard Test Method for Measuring Surface Frictional Properties Using the British Pendulum Tester, are great places to start in gaining understanding in what is required to create high traction COF surfaces. Using average roughness to consistently maintain a concrete floor’s surface texture may also be helpful in reducing the need of coatings and sealers while better understanding the performance of the floor over its lifetime.

To create resilient concrete, one must keep external slab moisture/contaminants out and internal moisture in. This can only be done by controlling vapour and water transmission. The reason why there are so many common problems (like the ones illustrated here) is due to designing concrete that allows moisture to freely travel through the concrete. Images courtesy Tao Group

Sustainable

As a result of the combined characteristics mentioned in the preceding sections, a concrete slab designed to keep out moisture will provide a long-lasting flooring solution which requires minimal maintenance to keep its natural beauty throughout the entire life cycle of the facility. If in case the floor ever does become covered with some other surface-applied finish, it has a much better chance of recovery when the applied flooring has worn out and needs to be removed.

An added benefit of concrete that naturally maintains its volume is its natural moisture mitigation attributes. This is a huge cost saving advantage where there will be installation of moisture-sensitive floorcoverings such as tile, carpet, or epoxy.

Resilient

By controlling volume loss, both structural and esthetic concrete problems diminish over the lifetime of the facility. In Bill Gate’s Fortune review of Robert Gordon’s “The Rise and Fall of American Growth,” he talked about new “super cements” that would offer the capability to “build infrastructure that lasts 10 times as long as the cement rebar approach.” This journey is already well under way with composite reinforcement, nano infused silica cements, Portland limestone cement (PLC), and metakaolin.

Wayfinding

How can someone be assured their design intentions are being met? The preference would be not having to depend on subjective opinions which tend to differ among the perspectives of the owner, architect, and contractor. Instead, the goal is to clearly define quantifiably what is to be achieved as a contract requirement in the specifications. Not until the work has been tested and verified to have met specific requirements can the work be determined to be acceptable.

A performance specification can avoid the visual inspection of what looks good at the time of substantial completion—only to wear off in a relatively short period, requiring costly reapplication of sealers.

Up until now, some of the concrete attributes mentioned in this article have been extremely difficult to achieve. An excellent concrete slab or polished concrete floor is the result of proper materials being applied by a skilled trade. Unless both are carefully identified in the contract documents, one will most likely come upon unsatisfactory results that do not meet expectations (Figure 4). Unfortunately, in the past, it has been all too often that at the very end of construction, with extreme pressure for impending occupancy, the owner is forced into accepting results neither expected nor desired—a tough pill to swallow when money is being exchanged for dissatisfaction just to get occupancy of the facility on time. Even less palatable is the ongoing additional expense that will be incurred to maintain a non-sustainable floor over the life of the building.

To avoid this dismal picture, it is extremely important to take the following steps throughout the construction process:

  1. The owner team must clearly understand the design intent that is attainable and can be achieved to protect their dollar investment.
  2. The design team must understand what is achievable and confirm the design intent with the client. The team must document all the requirements in the construction documents and defend the design intent throughout the entire construction process. One should beware product substitutions that claim to be the same as what is specified. Shop drawing reviews are critical to verify design intent will be met. The mockup also provides an opportunity to enforce quality assurance of the documents, to reduce the opportunities of unqualified contractors executing outside of their skillset, or worse, forcing a substitution of the floor itself.
  3. The construction team must be aware of the desired outcome of the documented design intent. This includes third-party qualified subcontractors that are certified and capable of producing the specified requirements. This must be confirmed during the contract procurement phase to avoid the all-too common confrontation that occurs when it was overlooked and not included in the contract sum.
  4. Finally, the supplier team must be responsible for supplying the products and materials capable of achieving the intended design. Again, all too often, some suppliers will try to suggest their products are the same or better than what was chosen and specified based on performance, not just appearance. Substitutions must only be considered when they have specific test results showing proven performance capabilities satisfying the specified requirements.

Conclusion

Polished concrete has recently become a popular design choice among interior designers due to its sustainable qualities and long-lasting esthetic. While it is a false belief that polished concrete is always less expensive than applied coverings, it is often less expensive in logistics and warehouse construction. True polished concrete is also one of the most economical and sustainable choices over the life of a building. It is important the entire project team has a clear understanding of what is meant by “polished concrete,” and then take the necessary steps to ensure the design intent is being met.

Construction professionals are the parents and guardians of their offspring (that is, the facilities they create). Some of the ancient concrete structures built by the Roman Empire and have survived millennia are cherished to this day. It is time again to make outstanding achievements in construction that will endure as economically viable, sustainable structures with durable, long-lasting, useful lives.

Author

Bill DuBois, AIA, CSI, CCS, is an architect with a passion for working with the entire construction project team, which includes owners, designers, constructors, and suppliers. DuBois assists in the decision-making processes necessary for efficient implementation of powerful design solutions and the creation of construction specifications. He can be reached at bill_dubois@gensler.com.

 

Chris Bennett, iSCS, CDT, is president of a North American concrete consultancy that provides owner and designer representation in the development of sustainable concrete solutions and risk reduction. He can be reached at www.BennettBuild.us.

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