Surface Profile Measurement Gauges

Why is Surface Profile Measurement Important?

Steel is often abrasive-blast cleaned or otherwise roughened prior to painting. The peak-to-valley height of the resultant "surface profile" is a critical and determining factor in the performance of applied paint and other protective coatings. A surface profile height that is too low may reduce coating bond strength (adhesion). Too high and the peaks may receive insufficient coverage leading to premature rusting, and often require additional paint (and labor costs to apply it) to cover the anchor profile.

Emerging research over the past 15 years has shown surface profile height is not the only important parameter. Peak density (also known as peak count), the number of peaks in the surface profile per unit area, has been shown to be a strong determinant of coating adhesion and resistance to corrosion. In fact, studies have found that peak density may be a better predictor of coating performance than peak-to-valley height.  

Surface profile height can also be relevant for other industries, as a way to quantify the profile height of non-skid surfaces, and to evaluate the Concrete Surface Profile (CSP) prior to applying coatings on concrete.

See below for more information about surface profile measurement and gauge solutions.

Product photo of the PosiTector 6000, coating thickness gauge for all metal substrates with cabled probe

Digital Surface Profile Gauges for Blasted Steel, Textured Coatings, and Concrete Profile

PosiTector SPG Surface Profile Gage

Surface Profile Gages use a digital depth micrometer fitted with a fine pointed probe to measure and record peak-to-valley surface profile eights in preparation for the application of coatings.

Conforms to ASTMD4417-B, ASTM D8271 (SPG TS only), AS 3894.5-C (with optional 30° tip), U.S.Navy NSI 009-32, Navy NAVSEA 009-32, US Navy NAVSEA PPI 63101-000, SSPC PA 17, SANS 5772, and others.

Product photo of the PosiTector 200, coating thickness gauge for non-metal substrates

Digital Replica Tape Reader for Blasted Steel and Textured Coatings

PosiTector RTR H Replica Tape Reader

Digital spring micrometers measure and record surface profile parameters using Testex Press-O-Film™ replica tape—producing a more accurate peak-to-valley surface profile height measurement for blasted steel and textured coatings.

Conforms to ASTM D4417, ISO 8503-5, NACE SP0287, SSPC-PA 17, SSPC-SP5, SP6, SP10, SP11-87T, and others.

Product photo of the PosiTest PC, non-contact uncured powder thickness gauge

Digital Replica Tape Reader for Measuring and Recording 2D/3D Surface Profile Parameters

PosiTector RTR 3D Replica Tape Reader

Digital replica tape imagers measure and record 14 common 2D/3D surface profile parameters using Testex Press-O-Film™ replica tape. Download high resolution .SDF files for further analysis (Advanced models only).

Conforms to ASME B46, ASTM D4417, ISO 8503-5, NACE SP0287, SSPC-PA 17, SSPC-SP5, SP6, SP10, SP11-87T, and others.

How is Surface Profile Measured?

Achieving optimal surface profile is a critical part of surface preparation* before the application of paint, coatings, liners, and cementitious overlays. By using standardized test methods and instrumentation, identifying optimal surface profile is possible—reducing the chance of coating adhesion failure, preventing corrosion, creating ideal paint finishes, and installing resilient cementitious overlays. Measuring anchor profile is essential for QA/QC and to achieve the high-performing and resilient coatings systems that clients expect.

*See also: Soluble Salt Testing and Environmental Monitoring

There are a variety of methods available to determine surface profile and concrete surface profile (CSP) peak-to-valley height, each with differing levels of accuracy and efficiency. Depending on whether a blasted steel surface or a concrete surface is being measured, different tools and instruments can be used.

The most common methods of determining surface profile on blasted steel surfaces include depth micrometers, replica tape readers, replica tape imagers, and drag stylus roughness gages.

Depth Micrometers for Blasted Steel

Depth micrometers fitted with a flat base and fine pointed probe such the PosiTector SPG, are a low per-test-cost method that use a spring-loaded tip which drops into the valleys of a blasted steel surface to measure peak-to-valley height. With a greater range than replica tape and most stylus roughness instruments, they are a quick and reliable way of determining surface profile.

To take a measurement with a PosiTector SPG Surface Profile Gage (digital depth micrometer):

prepare the surface with cleaning putty

1

Ensure the surface is free of all dust and other contaminants.

burnish the replica tape

2

Place the probe foot level on the surface to be measured.

measure with PosiTector RTR

3

The depth micrometer will display the profile height on-screen.

DeFelsko manufactures different models suited for a variety of applications—view the PosiTector SPG ordering guide for more information.

Replica Tape Readers for Blasted Steel

Replica tape readers such as the PosiTector RTR H or PosiTector RTR 3D use Testex Press-O-Film™ replica tape to determine the anchor pattern of the blasted steel substrate.  It is simple, relatively inexpensive, and is particularly useful on curved surfaces.

To take a measurement with a PosiTector RTR Replica Tape Reader (digital spring micrometer):

prepare the surface with cleaning putty

1

Prepare: Clean the surface with a putty to remove dust and other contaminants.

burnish the replica tape

2

Burnish: Place the replica tape (Testex Tape) on the substrate and burnish; the compressible foam within the tape forms a reverse replica of the surface.

measure with PosiTector RTR

3

Measure: Insert the replica tape between the PosiTector RTR's measurement anvils and take a reading.

Read, "Replica Tape -  A Source of New Surface Profile Information" for more information.

Stylus Roughness Testers for Blasted Steel

Drag stylus roughness instruments operate by dragging a stylus at a constant speed across the blasted steel surface being measured. The instrument records the up and down distances the stylus travels as it traverses across the surface and averages the vertical distance between the highest peak and lowest valley (Ra).

Some stylus roughness testers may leave scratches on the surface being measured, potentially contributing to future defects that could cause premature rusting and coatings failures. Additionally, the precise stylus assembly tends to be somewhat fragile, so field use may not be ideal. Lastly, stylus roughness tester’s probe tips can be prone to degradation and reading accuracy may suffer.

Read “Surface Profile - A Comparison of Measurement Methods” to learn more about these three methods and how they compare.

Other Methods to Measure Surface Profile on Blasted Steel

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Measuring Concrete Surface Profile

The most common methods of determining concrete surface profile (CSP) include depth micrometers, replica putty, and visual comparators.

Depth Micrometers for Concrete Surface Profile

Depth micrometers such as the PosiTector SPG TS, are a no per-test-cost method that use a spring loaded tip (60°—conically shaped) which drops into the valleys of a concrete surface profile to measure peak-to-valley height.

While less expensive methods are available, depth micrometers offer a means to quantitatively record readings in a statistically meaningful way.

Replica Putty

Replica putty is a means of creating a permanent replica of a CSP, similar in concept to replica tape. A 2-part compound is combined then pressed into the surface of a concrete slab. It is then removed and allowed to cure. Using a comparative reference, a subjective profile is assumed.

Comparative Methods

Using molded-rubber "chips"; subjective, comparative assessments may indicate a general profile of a concrete surface. Comparative methods are efficient in that they offer a quick check, but do not provide a quantitative means to measure and record the profile of a concrete surface.

Measuring Profile of Textured Coatings

The profile of textured coatings is often challenging to measure with most depth micrometers, stylus roughness instruments, and replica tape readers due to their greater peak-to-valley heights.

Depth Micrometers for Textured Surface Profile

Depth micrometers with an extended range of 0–60 mils (0–1,500 μm) such as the PosiTector SPG CS are an ideal choice for measuring textured coatings.

How to Select the Right Surface Profile Instrument for the Field

There are a variety of test standards and measurement methods available to determine surface profile. Generally, the test standard will be determined by the substrate being coated and the test method will be indicated in that test standard.

Surface profile gages such as the PosiTector SPG and replica tape readers such as the PosiTector RTR H and PosiTector RTR 3D are ideal instruments for measuring the peak-to-valley height.  Both types are ideal for measuring the anchor profile on blasted metals such as steel, aluminum, etc.

The PosiTector SPG TS is designed specifically to measure anchor pattern profile on concrete substrates prior to the application of coatings, paints, liners, or cementitious overlays.

Measuring surface profile (or concrete surface profile) assists the inspector in determining if optimal anchor profile has been achieved.

What is Surface (Anchor) Profile Height?

Surface (or anchor) profile is generally defined as the complex pattern of peaks and valleys found on a surface or substrate—often created by abrasive blast equipment or by power tools like a bristle blaster, air needle gun, or rotary peen. Specifically, surface profile height is defined differently depending on the test standard referenced. Some examples:

ASTM D7127 defines surface profile as, "…the positive and negative vertical deviations (peaks and valleys) are measured from a mean line approximately the center of the profile being evaluated.”
ISO 8503-1 defines it as, “…generally expressed as the height of the major peaks relative to the major valleys.”
ISO 4287—"Profile that results from the intersection of the real surface by a specified plane." Real surface being, "Surface limiting the body and separating it from the surrounding medium.

Paint and coating manufacturers will often specify ideal surface profile.

What is the Peak Density and Peak Count of a Surface Profile?

Peak Density and Peak Count measure the number of peak/valley pairs in a given length or area of the surface profile. They have been shown to be a strong determinant of coating adhesion and corrosion resistance. In fact, studies have found that peak density/count may be a better predictor of coating performance than peak-to-valley surface profile height alone.

Peak density is a 3D parameter that refers to the number of peaks per unit area- typically expressed in peaks/mm2 or peaks/in2. Peak Density can be measured with a PosiTector RTR 3D or laboratory imaging techniques, and is reported as Spd per ASME B46.1.

Peak count is a 2D parameter that refers to the number of peak/valley pairs- typically expressed in peaks/mm or peaks/in. Peak Count can be measured using the PosiTector RTR 3D or a drag stylus profilometer, and is reported as Rpc per ASTM D4417.

For more information on measuring Peak Density and Peak Count, read “Replica Tape - A Source of New Surface Profile Information

For more information on how Surface Profile affects coating performance, read “Replica Tape - Relating 3 Surface Profile Parameters to Pull-Off Adhesion

What is the importance of measuring Peak Density (Pd) in addition to Peak Height (H)?

It is generally accepted that the nature of abrasive blast cleaned steel surfaces is predictive of long-term coating performance. The corrosion industry does not fully understand the dynamics of this complex problem, but it has several measurable parameters available to it including peak height, peak density, surface area, angularity, sharpness, and shape.

Peak height is commonly measured today and is usually the only parameter reported. While its importance is undeniable, one parameter alone does not fully describe the dynamics of a coating/substrate relationship.

Peak density is also an important indicator of performance. Research has shown that it is strongly correlated with coating adhesion and resistance to corrosion- perhaps even more than Peak Height. For best coating adhesion and corrosion protection, peak count should be as high as possible while ensuring complete wetting of the prepared surface.

The ideal approach is to measure peak height (H) and Peak Density (Rpc). The PosiTector RTR 3D Replica Tape Reader measures peak height (H), peak density (Spd) and additional 2D/3D roughness parameters.

To learn more about how Surface Profile affects coating performance, read “Replica Tape - Relating 3 Surface Profile Parameters to Pull-Off Adhesion

What is Concrete Surface Profile (CSP)?

Concrete surface profile (CSP) can be defined as the peaks and valleys found on a concrete surface—similar to that of blast profile on steel. Concrete surface profile can affect the adhesion strength of coatings, linings, and cementitious overlays. Additionally, CSP affects the overall aesthetic and performance of the coating, lining, or overlay.

Manufacturers will often specify ideal CSP. Learn how concrete surface profile can be measured.

What Parameters are used to Represent Surface Profile?

Roughness is measured with readings characterized in either 2D or 3D parameters.

2D Parameters

Ra — Roughness average: arithmetic average of the absolute values of the profile height deviations within the evaluation length measured from the mean line

Rq — RMS roughness: root mean square average of the profile heights within the evaluation length measured from the mean line

Rz — Average maximum height of the profile: arithmetic average of the successive values of the maximum peak to deepest valley within each sampling interval calculated over the evaluation length

Rp — Maximum profile peak height: the distance between the highest point of the profile and the mean line within the evaluation length

Rv — Maximum profile valley depth: the distance between the deepest valley and the mean line within the evaluation length

Rt — Total profile height: the distance between the highest peak and the deepest valley within the evaluation length

Rpc — Peak count: number of peaks per unit length within the evaluation length

Rpc Boundary C1 — The boundary lines located equidistant above and below the profile mean line. A Peak is counted after the trace goes below the lower boundary line and above the upper boundary line. The default is 0.5 µm

3D Parameters

H — Average maximum peak-to-valley height: the distance between the anvils minus the 50.8 µm (2 mils) of incompressible film

Spd — Areal peak density: the number of peaks per unit area

Sa — Average roughness: the arithmetic average of the absolute values of the measured height deviations from the mean surface taken within the evaluation area

Sq — Root mean square roughness: the root mean square average of the measured height deviations from the mean surface taken within the evaluation area

Sz — Maximum area peak-to-valley height: the vertical distance between the maximum peak height and the maximum valley depth. Commonly referred to as St

Sp — Maximum area peak height: the maximum height in the evaluation area with respect to the mean surface

Sv — Maximum valley depth: the absolute value of the minimum height in the evaluation area with respect to the mean surface

What Test Standards are used to determine the Surface Profile of Blasted Steel Substrates?

The following standards are frequently used to determine the surface profile of a blasted steel substrate:

ASTM D4417—Standard Test Methods for Field Measurement of Surface Profile of Blast Cleaned Steel

Related products: PosiTector SPG, PosiTector RTR H, PosiTector RTR 3D

ASTM D4417 defines several methods for determining the surface profile of blast cleaned steel.*

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AS 3894.5—Site testing of protective coatings, Method 5: Determination of surface profile

Related products: PosiTector SPG, PosiTector RTR H, PosiTector RTR 3D, PosiTest, PosiTector 6000 (ferrous or ferrous/nonferrous probes)

AS 3894.5 defines peak-to-valley similarly to the language ISO 8503-1 in that it is concerned with the relative difference in height between the peaks and valleys of a test area.* Similar to ASTM D4417 (above), it provides several methods of obtaining a surface profile measurement:

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SSPC-PA 17—Determining Profile Compliance

Related products: PosiTector SPG, PosiTector RTR H, PosiTector RTR 3D

SSPC-PA 17 references several ASTM and ISO standards (such as ASTM D4417, ASME B46.1, ISO 4287, ISO 8503-4, and more) to establish certain definitions and test methods. Whereas ASTM D4417 sets out the procedure for preforming a single test, SSPC-PA 17 provides guidance on the frequency and locations of those tests.

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U.S. Navy NSI 009-32—Cleaning and Painting Requirements

Related products: PosiTector SPG, PosiTector RTR H, PosiTector RTR 3D

U.S. Navy NSI 009-32 is a thorough document aimed at cleaning and painting requirements to maintain U.S. Navy assets.* Referencing standards such as ASTM D4417 methods B & C (depth micrometers and replica tape, respectively.)

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SANS 5772—Preparation of steel substrates before the application of paints and related products — Surface roughness characteristics of blast-cleaned steel surfaces — Profile of blast-cleaned surfaces determined by a micrometer profile gauge

Related product: PosiTector SPG

The SANS 5772 test standard uses a micrometer profile gauge to determine surface profile on blast-cleaned steal surfaces.*

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What Test Standards are used to determine the Surface Profile of Concrete Substrates?

The following standards are frequently used to determine the surface profile of a concrete substrate:

ASTM D8271—Standard Test Method for the Direct Measurement of Surface Profile of Prepared Concrete

Related product: PosiTector SPG TS

ASTM D8271 standardizes the measurement of concrete surface profile (CSP).* Similar to Method B of ASTM D4417, it defines a depth micrometer as well as the testing procedure, number of readings, and reporting requirements.

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ASTM D7682—Standard Test Method for Replication and Measurement of Concrete Surface Profiles Using Replica Putty

ASTM D7682 instructs the user on how to use a two-part, fast-curing putty to create a reverse-replica of a concrete surface. Once cured, it can then be used with either an ICRI visual comparator (Method A) or a specially designed spring-less micrometer (Method B) to determine the surface profile of a concrete slab.

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Surface Profile

Coating performance is related to the profile height on a steel surface. DeFelsko offers three types of devices for measuring peak to valley surface profile height.

Why Surface Profile Measurement is Important

Steel is often abrasive blast cleaned or otherwise roughened prior to painting. The peak-to-valley height of the resultant surface profile is an important factor in the performance of applied protective coatings. Low profile may reduce coating bond strength (adhesion). Too high and the peaks may receive insufficient coverage and possibly rust prematurely. The costly application of more coating may be required if the profile is too high. For these reasons, surface profile should be measured prior to coating application to ensure that it meets contract specifications.

photo of surface being blasted