Coating failures rarely start with the paint itself. They often begin much earlier, at the surface preparation stage. Many projects run into issues like poor adhesion, uneven coating thickness, or early corrosion, only to discover that the root cause was an improper surface profile after blasting. It’s a small detail that can have big consequences.
In surface preparation for painting, blasting plays a critical role in creating the right surface profile. This profile consists of a pattern of peaks and valleys that directly influences how well a coating can anchor to the substrate. If the profile is too shallow, the coating may not adhere properly. On the other hand, if it’s too deep, the coating might fail to fully cover the valleys or become too thin over the peaks. Both scenarios increase the risk of corrosion or coating failure.
Measurement of surface profile helps to:
- Ensure the profile meets required standards (such as ISO, ASTM, and others)
- Determine if additional coating thickness is needed to achieve full coverage
- Evaluate the consistency of blasting across different areas
- Prevent future coating failures caused by poor adhesion or uneven application
What Is a Testex Micrometer?
A Testex micrometer is a thickness gauge specifically designed to measure Testex Replica Tape after it has been pressed onto a blasted surface. The process works as follows:
A piece of replica tape (Testex Press-O-Film), which contains a layer of compressible foam, is applied to the blasted surface. The tape is then burnished so the foam conforms to the peaks and valleys of the surface profile. Once removed, the tape retains an impression of that profile.
This impression is measured using the micrometer, which determines the surface profile depth by measuring the thickness between its anvils.
There are two common types of micrometers used for this purpose:
- Analog (dial) micrometer: Uses a manual dial scale for reading measurements, sometimes requiring conversion tables.
- Digital micrometer: Displays readings digitally, often with features like data storage, automatic conversion, and easier readability.
Testex micrometers are specifically engineered with the correct anvil dimensions, closing force, and parallelism to ensure accurate measurement of replica tape. This precision makes them an essential tool in maintaining coating quality and long-term performance.
How to Use a Testex Analog Dial Thickness Gage
Here’s a practical step-by-step guide to using a Testex analog micrometer.
1. Surface Preparation
Before burnishing, ensure the surface is clean and free from dust, blasting residue, or other contaminants. Use cleaning putty or another suitable method to remove debris that could affect the replica tape impression.
2. Select the Appropriate Replica Tape Grade
Choose the correct Testex replica tape (Coarse Minus, Coarse, X-Coarse, or X-Coarse Plus) based on the expected surface profile and the accuracy range required by the specification.
3. Apply and Burnish the Tape
Remove the replica tape from its backing paper. Place it onto the prepared surface and press around the foam area so it adheres properly. Using a Testex high-accuracy burnishing tool, apply firm pressure to the foam. Use either linear or circular motions until the foam develops a uniform gray appearance. This process typically takes between 10–60 seconds, depending on the roughness of the surface. Carefully remove the tape and inspect it to ensure there’s no contamination and that the impression is clear and consistent.
4. Set Up the Analog Micrometer
- Clean the micrometer anvils and set the dial to zero or a preset value (commonly 8 mils / 150 µm, depending on the guideline).
- Insert the replica tape between the anvils by pressing the lever. Ensure the foam area is centered. Slowly release the lever so the anvils close gently on the tape.
- Read the value from the dial and use the provided conversion table to determine the actual surface profile.
5. Repeat Measurements for Accuracy
At each measurement point, take at least two readings and calculate the average. If the difference between readings is too large, perform a third measurement to ensure reliability.
How to Use a Testex Digital Thickness Gage
The overall procedure is similar to the analog method, but digital micrometers simplify the process and reduce the risk of reading errors.
1. Surface Preparation and Tape Application
Follow the same steps as above: clean the surface, select the appropriate tape, and perform the burnishing process carefully.
2. Set Up the Digital Micrometer
- Clean the anvils and zero the instrument or select a preset mode if required.
- From the menu, choose the correct replica tape grade and confirm that the HL (High Limit) icon appears on the display.
- Press the lever to open the anvils, insert the replica tape, and slowly release the lever to close it.
3. Reading and Storing Results
Once the measurement stabilizes, the displayed value will blink, indicating a valid reading. If memory mode is enabled, the data will be stored automatically.
4. Reset After Measurement
After removing the replica tape, the device should return to approximately -50 µm (-2 mils). This indicates that the instrument is functioning correctly and is ready for the next measurement.
Transfer Data from Testex Digital Micrometer to Computer
Readings stored in memory can be downloaded to a computer for viewing, storing, and creating reports. Use the supplied cable and connect to the gage using the USB-C port on the side of the micrometer.
- USB Drive Mode: Retrieves data in a manner similar to a flash drive in .csv format. No software to install or internet connection required.
- PosiSoft Desktop: Powerful desktop software (PC/Mac) for downloading, viewing, printing and storing measurement data. Includes a customizable, templated PDF Report Generator.
Learn more at www.defelsko.com/posisoft
DeFelsko Distributor in Singapore
LFC PTE LTD is the authorized distributor of DeFelsko in Singapore. Our expert team is ready to assist you in selecting the ideal instruments to meet your specific requirements.
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