{"id":210573,"date":"2025-01-13T13:18:56","date_gmt":"2025-01-13T18:18:56","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=210573"},"modified":"2025-05-29T14:34:03","modified_gmt":"2025-05-29T18:34:03","slug":"prohibit-polished-concrete","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/prohibit-polished-concrete\/","title":{"rendered":"Refine versus shine: Defining and defending design intent with refined concrete"},"content":{"rendered":"

By Kristina Abrams, AIA, LEED AP, CDT, CCS, Chris Bennett, CSC, iSCS, CDT, Bill DuBois, CSI, CCS, AIA, \u2028Melody Fontenot, AIA, CSI, CCCA, CCS, Kathryn Marek, AIA, CSI, CCCA, NCARB, SCIP, Keith Robinson, RSW, FCSC, FCSI, LEED AP, Ryan Stoltz, P.E., LEED AP, Vivian Volz, CSI, AIA, LEED AP, SCIP<\/strong><\/p>\n

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Photo courtesy Tao Group Solutions<\/em><\/figcaption><\/figure>\n

After years of grappling with client callbacks, legal disputes, and financial losses from poor polished concrete installations, the industry has reached a breaking point: prohibit polished concrete. The cycle of repeated failures can no longer continue, prompting the urgent question\u2014what now?<\/p>\n

Owners and design teams are not protected by today\u2019s inadequate and vague polished concrete specifications. From floors failing before substantial completion to skyrocketing change orders for never-ending densifier applications to the billions lost through delayed schedules, legal disputes, and contingency hemorrhaging, enough is enough.<\/p>\n

What was once promised as a durable, low-maintenance flooring solution has been replaced by a patchwork of temporary sealers, densifiers, and polyureas\u2014products that often require reinstallation almost immediately after application. Despite calls for clarity in specification language with accurate descriptions of work results, the definition of polished concrete has broadened to accommodate any floor finish that produces a shine. The industry urgently needs a specification framework that is measurable, verifiable, and defensible.<\/p>\n

Without a quantifiable specification to convey contract requirements, project teams will continue to be handed polished concrete floors that are ripe for change orders and expensive to maintain. Contractors and design teams will continue to pay out contingencies without understanding what went wrong and how to protect themselves in the future. Thus, there is a need for a new solution to achieve a more reliable result that exceeds expectations. Building on straightforward material testing and proven project successes, the industry is making significant strides toward developing accountable language and precise definitions that can be universally specified to address concrete floor challenges. The focus has shifted to demanding results\u2014quantifiable, repeatable, and validated outcomes through physical testing of the finished product delivered to the client.<\/p>\n

A new MasterFormat number and title are being proposed to establish a common language and eliminate the misinterpretations that led to the current challenges: 03 35 44\u2013Refined Concrete Finishing. The remainder of this article will detail the key elements of the proposed new specification, highlighting significant differences and improvements over previous polished concrete sections. It will also examine suppliers\u2019 confusing and conflicting language, contributing to the misunderstandings and missteps that brought the industry to this point.<\/p>\n

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The refinement differences are clearly visible in this polished concrete image. It is likely that the benchmarks for this polishing scope were gloss-based and the design team had no way to protect the owner \u2028from this outcome. Photo courtesy Vivian Volz<\/em><\/figcaption><\/figure>\n
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Despite this retail store being open for less than 18 months, \u2028the polished concrete finish has failed leaving an unsightly, pitted, unrefined concrete surface. Photo courtesy Bennett Build<\/em><\/figcaption><\/figure>\n

The polished concrete problem<\/strong><\/h2>\n

The design industry has struggled with polished concrete for years. Contradictory weak specification language has left owners and design teams to simplify their aesthetic preferences based on photo representations and rely on marketing information about durability and low maintenance without proof. Inevitably, projects continue to have mixed results, where owners must accept problematic floors because they cannot be rejected contractually.<\/p>\n

The language used to describe polished concrete lacks precision and clarity, making it difficult for owners to understand what they are purchasing, tough for designers to specify, and unclear for contractors to understand what they are required to build. Terms such as \u201chigh gloss,\u201d \u201creflective,\u201d \u201csustainable,\u201d and \u201cdurable\u201d can be highly subjective and used differently by manufacturers. This ambiguity can lead to misinformed choices based on marketing rather than factual performance characteristics.<\/p>\n

The categorization of polished concrete into various levels of sheen can confuse even veteran professionals, as the criteria is broad, and producer results can vary widely. The Concrete Polishing Council (CPC) provides four appearance levels using Distinctness of Image (DOI) gloss with Level 1: flat, Level 2: satin, Level 3: polished, and Level 4: highly polished with gloss and reflectivity as the measurement guideline. These levels, from CPC\u2019s Exposed\/Polished Concrete Exposure Chart, are defined by image distinction, gloss value, and haze\u2014characteristics based on reflection and lighting, not actual physical characteristics of the concrete.<\/p>\n

There are countless floor finishes (e.g.<\/em> grind and seals, burnished polish concrete, etc.) and many ways to achieve gloss levels. When the path to the work result is only gloss, contractors will seek out the most economical way to fit the definition of polished concrete and meet the required DOI gloss level. Despite the design team\u2019s best efforts in using the specification guidelines provided by manufacturers, results often disappoint. Sometimes, that same spec language is used to defend the undesired outcome\u2014rather than serving their intended purpose to ensure the desired quality results for the owner.<\/p>\n

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Both refined concrete and polished concrete score high marks on aesthetics, but the cost of ownership \u2028increases with polished concrete while the cost of ownership decreases with refined concrete. Maintenance \u2028teams at Waco ISD are picking up the skills to measure, meter, and maintain exposed concrete surfaces \u2028without stripping and sealing. Photo courtesy Bennett Build<\/em><\/figcaption><\/figure>\n

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What is polished concrete, exactly?<\/strong><\/h2>\n

According to CPC, polished concrete is \u201cthe act of changing a concrete floor surface, with or without aggregate exposure, to achieve a specified level of finished gloss.\u201d The definition further states there are different types of polished concrete: \u201cBonded Abrasive Polished Concrete, Burnished Polished Concrete, or Hybrid Polished Concrete.\u201d<\/p>\n

CPC defines bonded abrasive polished concrete as \u201cthe multi-step operation of mechanically grinding, honing, and polishing a concrete floor surface with bonded abrasives to cut a concrete floor\u2026 to achieve a specified level of CPC-defined finished gloss.\u201d Burnished polished concrete is defined by CPC as \u201cthe multi-step operation of mechanical friction-rubbing a concrete floor surface with or without waxes or resins to achieve a specified level of CPC defined finished gloss.\u201d By definition, the burnished version of polished concrete can include coating the floor with waxes and resins. The CPC notes that this \u201cyields a less durable finish and requires more maintenance than bonded abrasive polished concrete.\u201d<\/p>\n

Hybrid polished concrete combines burnished polished concrete, bonded abrasive concrete, or anything in between that attempts \u201cto achieve the specified level of CPC-defined finished gloss.\u201d<\/p>\n

The emphasis on shine<\/strong><\/h2>\n

This emphasis on achieving gloss (specular gloss, DOI gloss, etc.) has led to practices prioritizing aesthetic qualities over functional durability. The pursuit of shine in polished concrete usually involves the use of chemical sealers, sometimes called \u201cguards,\u201d latex, acrylic, and various grouts, as well as solid epoxy tooling, which coats the floor as it is superheated and resin is transferred via friction rubbing to fill and hide scratches and imperfections with a thin shiny coating rather than correct the concrete surface. Whether a floor is refined without topical treatments or coated with resins and sealers, CPC classifies all these floor types as \u201cpolished concrete\u201d if they achieve gloss\u2014sometimes.<\/p>\n

The glossary page of the CPC includes a definition for surface-coated concrete, indicating that \u201csurface-coated concrete (waxes and resins) does not conform to the definition of polished concrete. It is the operation of applying a film-forming coating to a concrete floor surface to achieve a specified level of finished gloss.\u201d In other words, the defined end result of surface-coated concrete is essentially the same as burnished polished concrete. By definition, both aim to achieve a level of gloss. This means substitutions involving any cheap grind and seal or temporary burnished film-forming material contractually meet the design intent\u2014despite not meeting the design intent. How can a specifier reject a work result that is both allowed and not allowed?<\/p>\n

While concrete is inherently durable, an overly aggressive dry polishing process often compromises the material\u2019s integrity by destroying the finished slab\u2019s most durable top \u201cskin,\u201d making it more susceptible to staining, scratching, and general wear. This degradation necessitates an initial grout coat and more frequent lifecycle refinishing and maintenance, contradicting initial claims of a problem-free floor. Thus, while the polished surface may initially appear appealing and shiny, its long-term viability (compounded by frequent coating applications) is questionable.<\/p>\n

Concrete refining<\/strong><\/h2>\n

The refining process is guided by initial measurements of average roughness (Ra) and Mohs hardness readings, which will be discussed in detail shortly. Refining includes wet mechanical refinement with power trowels or grinding equipment and chemical components that react with cement particles and free lime to stabilize and reshape the surface. Cement binds to form concrete. The unhydrated cement in the concrete tailings gets reincorporated to strengthen the surface concrete, and the newly exposed cementitious content has the opportunity to hydrate and strengthen the surface while it is in a malleable state, reworked back into itself, and then refined to provide an improved denser surface. Many professionals may be unaware that the top surface of a concrete slab can be reworked and refined after initial hardening, making refined concrete appropriate for a slab that is 40 years old or brand new.<\/p>\n

The top 19 to 25 mm (0.75 to 1 in.) of a concrete slab is most susceptible to physical damage and the effects of nature. Decreased moisture content (MC) and lowered relative humidity (RH) from poor external curing practices also impact the durability of the top layer. This can significantly reduce the surface strength of concrete when the humidity drops below 80 percent as the hydration of the cement particles nearly stops below this level and does not restart when RH increases. The concrete refining process provides immense value and redefines the finishing and maintenance processes to help answer many of these issues.<\/p>\n

A refined slab exhibits the same aesthetic capabilities of polished concrete (aggregate exposure levels, color, and DOI gloss) without coatings, sealers, and resinous grouts common with polished concrete. In fact, the concrete itself becomes the grout during the refinement process, addressing pop-outs, cracks, and other small voids. Refined concrete creates a measurable, monolithic floor slab with its surface integrity intact.<\/p>\n

\u201cUnlike polished concrete, which may be a mix of resinous and cementitious materials, the single concrete matrix of refined concrete will accept color, react with humidity, and respond to its environment in more predictable and aesthetically pleasing ways,\u201d says Chris Bishop, president of the National Concrete Refinement Institute (NCRI).<\/p>\n

Refining concrete eliminates topical impurities that have become standard with most \u201cpolished concrete\u201d methodologies and results in more flexibility with the final finish, such as staining, dyeing, or even maintaining a truly refined concrete surface, but for much less money.<\/p>\n

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Microsurface benchmarks for refined concrete are measured in microinches (\u00b5in) or in micrometers (\u03bcm) by a device called a profilometer. Additional readings for gloss or gloss clarity may be taken in conjunction with surface micro texture readings after verification of physical refinement. Along with the Mohs scratch test, these measurements provide important contractual goals to describe design intent as well as defend against resinous diamond tooling, epoxy grouts, and other clear coat substitutions that do not provide the durability of refined concrete. Referenced from A New Concrete Glossary \u2028by Keith Robinson, Bill DuBois, Rae Taylor, Chris Bennett, and John Guill. Image courtesy Mitutoyo Bulletin No. 2229<\/em><\/figcaption><\/figure>\n

Refined concrete benchmarks<\/strong><\/h2>\n

Physical readings from the concrete itself quantify performance benchmarks for refined concrete. Aesthetic benchmarks from the coating industry (DOI gloss, lumen levels, etc.) can also be used. Still, physical benchmarks ensure resilience, durability, simple maintenance, and a long service life that owners associate with exposed concrete floors. The three most important physical benchmarks are Ra, Mohs hardness, and dynamic coefficient of friction (DCOF).<\/p>\n

Average roughness (Ra)<\/strong><\/h2>\n

These microsurface benchmarks for refined concrete are measured in microinches (\u03bcin) or micrometers (\u03bcm) per the American Society of Mechanical Engineers (ASME) B46.1-2019 (R2019), Standard for Surface Texture (Surface Roughness, Waviness, and Lay)<\/em>. This standard provides a practical method for measuring Ra on a surface.<\/p>\n

Scott Langerman, P.E., of Langerman Engineering says, \u201cMeasuring the roughness average (Ra) provides input for concrete surface refinement. The Ra test is performed with equipment (profilometers) that measure the roughness\/smoothness to the micro-inch. Data are then used to determine steps for the initial grinding process, minimizing surface micro fractures and maximizing refinement. After refinement is done, the Ra test is then performed again to determine that project specifications have been achieved.\u201d<\/p>\n

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Architects, contractors, and material science students learning how to process concrete surfaces and achieve consistent refinement \u2028as measured through average roughness (Ra) at University of Alberta\u2019s campus. Photo courtesy Keith Robinson<\/em><\/figcaption><\/figure>\n

Ra notes<\/em><\/h3>\n