Proper bonding of coatings and linings to concrete surfaces requires proper cleaning and frequently requires the concrete to be roughened to increase the surface area. The roughness, also known as surface profile, can be imparted into concrete by abrasive blast cleaning, acid etching, or various impact/scarifying power tools. The resulting surface profile depth can influence coating/lining adhesion and performance. Coating/lining manufacturers and/or facility owners frequently specify cleaning and roughening of the concrete surface prior to product installation.
Traditionally, the surface profile (roughness) of prepared concrete has been assessed visually using Concrete Surface Profile (CSP) Chips such as those described in Guideline No. 310.2R, Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair produced by the International Concrete Repair Institute (ICRI). This guideline summarizes the capabilities and limitations of the various methods used to prepare concrete surfaces for the application of coatings and repairs. Chips are arguably the most widely recognized and frequently specified method to assess concrete roughness; however, this method is qualitative and requires some judgment by the individual inspector.
More recently, digital options such as the PosiTector SPG TS have allowed inspectors to measure Concrete Surface Profile using a digital, quantitative method, in accordance with ASTM D8271. While this method has significant benefits, its adoption was previously limited by difficulty cross-referencing between the CSP Chip method (where the chip number that most closely resembles the surface finish of the concrete is reported), and the Digital Depth Micrometer method (where the profile in mils is reported).
However, in a recent paper by Beamish and Corbett (2022)1, a study was undertaken to create a cross reference table so that the two methods could be used interchangeably. Details about the procedure used to create that table are featured in Appendix A of this article.
ICRI chips are available as a set of 10 with varying degrees of surface roughness indicative of the different methods of concrete surface preparation such as acid etching, grinding, shotblasting, abrasive blasting, and scarification. These chips are designed as a visual and tactile comparator for identifying the degree of surface roughness. The user compares prepared concrete to the CSP chips and reports the chip number that most closely resembles the surface. Many jobs will specify the type of surface preparation required.
The ICRI CSP Chips are approximately 16 square inches (3.5” x 4.5”) and are designed to replicate 10 surface profiles as shown in Table 1.
ASTM D8271, Standard Test Method for the Direct Measurement of Surface Profile of Prepared Concrete describes an alternative procedure for acquiring measurements directly from the prepared concrete using an electronic depth micrometer such as the PosiTector SPG TS. These instruments have a flat base and a spring-loaded tip which drops into the valleys of the surface profile.
The PosiTector SPG TS gage’s flat base rests on the highest peaks and each measurement is the distance between the highest local peaks and the particular valley into which the tip is projected. Instruments of this type are ideal for measuring up to 6 mm of profile height directly on the surface without the need of replica putty or the vagueness of visual comparators. They are ideal for measuring the surface profile of concrete that has been prepared by blasting, scarifying, grinding, acid etching, and other preparatory methods.
Unlike qualitative visual comparators, ASTM D8271 is quantitative but is not yet widely specified. A study was conducted using rigid, epoxy-cast replicas of seven of the ten ICRI CSP Chips (CSP 1-7) and the ASTM D8271 method utilizing the PosiTector SPG TS digital depth micrometer.
The Look-up Table shown below enables a specifier to easily convert a qualitative assessment (e.g., ICRI CSP 1-7) to a quantitative range for surface profile on concrete. Ranges are only shown for CSP 1-7 since only those were studied during this research and the values are rounded. Tolerances were established based on the standard deviation data.
Unlike subjective visual assessments, the digital PosiTector SPG TS Concrete Surface Profile Gage provides real quantitative analysis in the field of roughness measurement. The easy-to-use PosiTector SPG offers a fast measurement speed of over 50 readings per minute and onboard memory for record keeping, review, and sharing with other users for further analysis.
Featuring a powerful Statistics Mode to display average, standard deviation, and min/max profile depth; the American-made PosiTector SPG is ideal for quickly and accurately analyzing large surfaces. The HiLo Alarm audibly and visibly alerts when measurements exceed user-specified limits. With a durable alumina wear face and tungsten carbide probe tip, the PosiTector SPG was built for long life and continuous accuracy.
To determine conformance to concrete surface profile specifications, AMPP Standard Practice SP21513, Procedure for Determining Conformance to Concrete Surface Profile Requirements outlines where to take measurements and how many measurements to take, and provides guidance on how to identify non-conforming areas. This standard describes a procedure suitable for laboratory and field use to determine conformance to specified surface profile on concrete substrates using Method 1: Depth micrometer as described in ASTM D8271 and Method 2: Concrete Surface Profile (CSP) Chips (CSP 1-10) as described in ICRI Guideline No. 310.2R.
The study design was initially composed of methodologies that were specifically chosen to enable specifiers to convert from qualitative surface profile assessment techniques to quantitative ranges.
The ICRI CSP Chips are made from a gray, pliable rubber material that is acceptable for most applications but was problematic for this research. The probe of the digital depth micrometer intended to be used to obtain measurements of surface profile on these CSP Chips contains a stainless steel, spring-loaded 60° cone-shaped point that would penetrate the pliable rubber and generate false high values. Therefore, silicone molds of CSP 1-7 were made and a black epoxy was cast into each mold, effectively creating exact replicas of CSP 1-7 in hardened epoxy that would be unaffected by the micrometer probe and pressure.
Once the epoxy was fully cured, three sub-batches of 15 readings/each were obtained on CSP 1-7 replicas by 6 technicians (independently) using a PosiTector SPG TS digital depth micrometer (gage; Figure 6) with a range up to 250 mils and stored in the gage memory for subsequent analysis.
In every case, the epoxy putty replicas (indirect method of measurement) produced a greater surface profile height than the direct measurement method (i.e., measurements directly from the CSP chips) and the standard deviation of the data was greater.
Table 2 contains the results; Graph 2 illustrates the data.
Proper bonding of coatings and linings to concrete surfaces requires proper cleaning and frequently requires the concrete to be roughened to increase the surface area. The roughness, also known as surface profile, can be imparted into concrete by abrasive blast cleaning, acid etching, or various impact/scarifying power tools. The resulting surface profile depth can influence coating/lining adhesion and performance. Coating/lining manufacturers and/or facility owners frequently specify cleaning and roughening of the concrete surface prior to product installation.
The CSP Chips produced by ICRI are arguably the most widely recognized and most frequently specified method to assess concrete roughness; however, this is qualitative and requires some judgement. The procedures described in ASTM D8271 are quantitative but are not widely specified at the time of this writing.
This study revealed that there are differences between taking direct measurements from known surfaces (i.e., the ICRI CSP panels) and obtaining indirect measurements from an epoxy putty casting of those same known surfaces. Therefore, it is important that the specifier indicate which method is to be used when quantitative methods are invoked in the contract documents (ASTM D8271).
The Look-up Table enables a specifier to easily convert a qualitative method to a quantitative range of surface profile on concrete. Ranges are only shown for CSP 1-7 since only those were studied during this research. Values are rounded. Also, since direct measurement from the concrete is feasible, there is little value in generating replicas of the concrete surface using the epoxy putty (and subsequently measuring it using a micrometer) unless a permanent record of the concrete roughness is desired.
1 Beamish M. & Corbett, W, Correlating Qualitative Surface Profile Assessment Methods to Quantitative Methodology on Prepared Concrete. AMPP Conference 2022, San Antonio, Texas.
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