ASTM D4138-94(1999)

Standard Test Methods for Measurement of Dry Film Thickness of Protective Coating Systems by Destructive Means

SCOPE
1.1 These test methods cover the measurement of dry film thickness of coating films by microscopical observation of precision angular cuts in the coating film. Use of these methods usually requires repair of the coating film.  
1.2 Three test methods are provided for measuring dry film thickness of protective coating system:  
1.2.1 Test Method A--Using groove cutting instruments.  
1.2.2 Test Method B --Using grinding instruments.  
1.2.3  Test Method C --Using drill bit instruments.  
1.3 The substrate should be sufficiently rigid to prevent deformation of the coating during the cutting process. The surface may be flat or moderately curved (pipes as small as 1 in. (25 mm) in diameter may be measured in the axial direction).  
1.4 The range of thickness measurement is 0 to 50 mils (0 to 1.3 mm).  
1.5 The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are for information only.  
1.6 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Dec-2000
• Technical Committee: D01 - Paint and Related Coatings, Materials, and Applications
• Drafting Committee: D01.23 - Physical Properties of Applied Paint Films

Relations

• Replaced By: ASTM D4138-94(2001)e1 - Standard Test Methods for Measurement of Dry Film Thickness of Protective Coating Systems by Destructive Means
• Effective Date: 01-Jan-2001
• Referred By: ASTM D5064-16a(2021) - Standard Practice for Conducting a Patch Test to Assess Coating Compatibility
• Effective Date: 01-Jan-2001
• Referred By: ASTM D3794-22 - Standard Guide for Testing Coil Coatings
• Effective Date: 01-Jan-2001
• Referred By: ASTM D3276-21 - Standard Guide for Painting Inspectors (Metal Substrates)
• Effective Date: 01-Jan-2001
• Referred By: ASTM D7378-16 - Standard Practice for Measurement of Thickness of Applied Coating Powders to Predict Cured Thickness
• Effective Date: 01-Jan-2001
• Referred By: ASTM D5702-18(2022) - Standard Practice for Field Sampling of Coating Films for Analysis for Heavy Metals
• Effective Date: 01-Jan-2001
• Referred By: ASTM D6577-15(2019) - Standard Guide for Testing Industrial Protective Coatings
• Effective Date: 01-Jan-2001
• Referred By: ASTM D7893-13(2018) - Standard Guide for Corrosion Test Panel Preparation, Testing, and Rating of Coil-Coated Building Products
• Effective Date: 01-Jan-2001
• Referred By: ASTM D7835/D7835M-19 - Standard Test Method for Determining the Solvent Resistance of an Organic Coating Using a Mechanical Rubbing Machine
• Effective Date: 01-Jan-2001
• Referred By: ASTM D5402-19 - Standard Practice for Assessing the Solvent Resistance of Organic Coatings Using Solvent Rubs
• Effective Date: 01-Jan-2001
• Referred By: ASTM D6137-97(2018) - Standard Test Method for Sulfuric Acid Resistance of Polymer Linings for Flue Gas Desulfurization Systems
• Effective Date: 01-Jan-2001
• Referred By: ASTM D2134-19 - Standard Test Method for Determining the Hardness of Organic Coatings with a Sward-Type Hardness Rocker
• Effective Date: 01-Jan-2001
• Referred By: ASTM D4752-20 - Standard Practice for Measuring MEK Resistance of Ethyl Silicate (Inorganic) Zinc-Rich Primers by Solvent Rub
• Effective Date: 01-Jan-2001
• Referred By: ASTM D6943-15(2019) - Standard Practice for Immersion Testing of Industrial Protective Coatings and Linings
• Effective Date: 01-Jan-2001
• Referred By: ASTM D6237-19 - Standard Guide for Painting Inspectors (Concrete and Masonry Substrates)
• Effective Date: 01-Jan-2001

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 4138 – 94 (Reapproved 1999)
Standard Test Methods for
Measurement of Dry Film Thickness of Protective Coating
Systems by Destructive Means
This standard is issued under the fixed designation D 4138; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Summary of Test Methods
1.1 These test methods cover the measurement of dry film 3.1 The three methods are based on measurement of dry
thickness of coating films by microscopical observation of film thickness by observation of angular cuts in the coating
precision angular cuts in the coating film. Use of these methods through a microscope having a built-in reticle with a scale.
usually requires repair of the coating film. Each method employs different instruments to make the cut in
1.2 Three test methods are provided for measuring dry film the coating.
thickness of protective coating system: 3.2 Test Method A—Uses a carbide tipped wedge to cut a
1.2.1 Test Method A—Using groove cutting instruments. groove in the coating. The groove is cut at a precise angle to the
1.2.2 Test Method B—Using grinding instruments. surface. Three wedge angles are available.
1.2.3 Test Method C—Using drill bit instruments. 3.3 Test Method B—Uses a high speed rotary grinding disk
1.3 The substrate should be sufficiently rigid to prevent or drum type bit to cut partial cylindrical cavities in the
deformation of the coating during the cutting process. The coating. Axes of the cavities can be oriented at three angles of
surface may be flat or moderately curved (pipes as small as 1 inclination to the surface.
in. (25 mm) in diameter may be measured in the axial 3.4 Test Method C—Uses a specific angle tip drill bit to cut
direction). a conical cavity in the coating.
1.4 The range of thickness measurement is 0 to 50 mils (0 to
4. Significance and Use
1.3 mm).
4.1 The use of these test methods is not necessarily limited
1.5 The values stated in inch-pound units are to be regarded
as the standard. The values given in parentheses are for by the type of substrate material as are nondestructive
magnetic-type means.
information only.
1.6 This standard does not purport to address all of the 4.2 Individual coats or the overall thickness of a coating
system can be measured by these methods.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
5. Test Method A—Groove Cutting Instruments
priate safety and health practices and determine the applica-
5.1 Apparatus
bility of regulatory limitations prior to use.
5.1.1 Scribe Cutter and an Illuminated Microscope, with
2. Referenced Documents
Measuring Reticle. The scribe cutter and illuminated micro-
scope may be combined as a single instrument (see Fig. 1).
2.1 ASTM Standards:
D 823 Practices for Producing Films of Uniform Thickness The instrument calibration shall be performed by taking
measurements on applied films of known thickness (see Test
of Paint, Varnish, and Related Products on Test Panels
D 1005 Test Method for Measurement of Dry-Film Thick- Method D 1005).
5.1.2 Tungsten Carbide Cutting Tips shall be designed to
ness of Organic Coatings Using Micrometres
D 1186 Test Methods for Nondestructive Measurements of provide a very smooth incision in the paint film at a precise
angle to the surface (see Fig. 2 ). Separate tip designs (angles)
Dry-Film Thickness of Nonmagnetic Coatings Applied to
a Ferrous Base shall provide cuts of known slopes such as 1 to 1, 1 to 2, and
1 to 10. These tips shall be nominally designated 13,23, and
D 1400 Test Method for Nondestructive Measurement of
Dry Film Thickness of Nonconductive Coatings Applied to 103 to indicate the ratio of the lateral measurement to vertical
depth. The lateral measurement is represented by the reticle
a Nonferrous Metal Base
markings and this vertical depth is represented by the coating
These test methods are under the jurisdiction of ASTM Committee D33 on
Protective Coating and Lining work for Power Generating Facilities and is the direct The sole source of supply of the Tooke gage known to the committee at this
responsibility of Subcommittee D33.03 on Quality Systems. time is MicroMetrics, P.O. Box 13804, Atlanta, GA 30324. If you are aware of
Current edition approved Jan. 15, 1994. Published March 1994. Originally alternative suppliers, please provide this information to ASTM Headquarters. Your
published as D 4138 – 82. Last previous edition D 4138 – 88. commments will receive careful consideration at a meeting of the responsible
2 1
Annual Book of ASTM Standards, Vol 06.01. technical committee, which you may attend.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 4138
reticle scaled from 0 to 100 divisions (see Fig. 3). The total
viewing field of the microscope shall be approximately 125
mils (3.18 mm).
NOTE 1—A photomicrographic adapter is available with some micro-
scopic instruments that allows photographs to be taken through the view
finder.
5.2 Test Specimens
5.2.1 If multiple coats of paint are to be measured, succes-
sive contiguous coats should be of contrasting colors to aid
sharp discrimination of interfaces.
5.2.2 Generally, test specimens shall be prepared (as test
panels) or chosen (as sites on a structure) to be representative
of localized coating thickness and variability.
5.2.3 For test panels, if measurement repeatability is desired
for a particular paint system, care shall be taken in panel
preparation. Coating shall be uniformly applied in accordance
with Test Method D 823. Panels shall be placed in a horizontal
position during drying. Uniform application thickness shall be
verified by another measurement method such as Test Methods
D 1005, D 1186, or D 1400.
5.3 Procedure
5.3.1 Select a test panel or choose a site for the thickness
measurement.
5.3.2 Using an appropriate surface marker of contrasting
color, mark a line on the surface approximately 2-in. long
(51-mm) where the thickness measurement will be made.
FIG. 1 Tooke Inspection Gage
(A)
FIG. 2 Geometry of Thickness Measurement
(B)
FIG. 2 Grooves Made by 13,23, and 103 Cutting Tips
(continued)
film thickness. Metal guide studs on the gage body shall,
together with the cutting tip, form a firm base to ensure that the
tip aligns vertically with the painted surface for a precisely
aligned incision.
FIG. 3 Typical View Through Microscope of Tooke Inspector
5.1.3 Illuminated, 50-Power Microscope shall contain a Gage Showing Reticle
D 4138
5.3.3 Select a cutting tip based on estimated film thickness system thickness as follows:
as follows:
Coating System Thickness, Conversion
Position
mils (μm) Factor
Thickness Range, Conversion
Tip
mils (μm) Factor
13 20 to 50 (500 to 1250) 1.0
23 2 to 20 (50 to 500) 0.5
13 20 to 50 (500 to 1250) 1.0
43 0 to 3 (0 to 75) 0.25
23 2 to 20 (50 to 500) 0.5
103 0to3(0to75) 0.1
If thickness is unknown, make a trial determination in 23
If thickness is unknown, make a trial determination with the position.
23 tip. 6.3.4 Install the tungsten carbide grinding tip so that it
5.3.4 To cut a groove, grasp the gage with the studs and extends 1 ⁄4 in. (31.75 mm) from the chuck mouth.
cutting tip firmly forming a tripod on the painted surface. Place 6.3.5 The cut is made by grinding a groove through the
the gage at right angles to and about 2 in. (51 mm) perpen- coating system down to the substrate.
dicularly from a marked line.
NOTE 2—Take care to hold
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