What Is Adhesion?
Adhesion test is the test in which the adhesion of the coating to the substrate is evaluated by cross cutting (ISO 2409 / ASTM D3359) or pull-off (ISO 4624) methods. The first method gives classification, the second gives quantitative strength.
Purpose of Adhesion
The purpose is to verify that the coating can carry service loads without separating from the substrate.
Which Products Is Adhesion Applied To?
- Industrial paints and primers
- Toz kaplamalar
- Automotive paint systems
- Galvanized and metallic coatings
In Which Sectors Is Adhesion Used?
Standards Related to Adhesion
- ISO 2409 (cross cutting)
- ASTM D3359
- ISO 4624 (tear off)
- ASTM D4541
Adhesion Conditions
- Cross-cut
- Blade spacing defined in the standard according to the coating thickness; the result is given as a class 0–5
- pulling away
- The pasted pin is withdrawn at standard speed; breaking strength is measured in MPa
- Kopma tipi
- Adhesion or cohesion failure is reported separately
- Conditioning
- The coating must be fully cured; Conditioned in the environment defined in the standard
Equipment for Adhesion
- Cross cutting tool and standard tape
- Pull-out device (adhesion tester) and pins
- Coating-thickness gauge
- Conditioning room
Sample Requirements for Adhesion
- The coating must be fully cured; early testing gives low value
- Coating thickness determines blade spacing and must be measured
- The adhesive must be stronger than the coating when pulled off.
- Measurement points should be selected representatively
Duration of Adhesion
Typically 2–4 days including conditioning.
Adhesion Procedure
- 1Coating thickness is measured.
- 2Blade spacing or pin is selected according to the method.
- 3The cross cut is applied and the tape is pulled; or the pin is glued and pulled.
- 4The result is classified or the strength is calculated.
- 5The type of rupture is determined and photographed.
Adhesion Acceptance Criteria
The acceptance criterion is given in the specification: maximum class in transverse shear (e.g. not exceeding class 1) or minimum strength in pull-out.
Evaluation of Results
Cross cutting and pulling do not measure the same magnitude and their results are not interchangeable. Testing performed before the coating is fully cured does not represent actual adhesion. When the adhesive breaks during pulling, it invalidates the result.
Adhesion Report
- Standard and method applied
- Coating system and thickness
- Conditioning conditions
- Grade or breaking strength
- Break type and images
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- Paint and coating specifications
- ISO 12944 (korozyon koruma sistemleri)
Paint and Coating Testing — What Does This Testing Field Cover?
The section below describes the field that the Adhesion test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Paint and coating testing measures the adhesion of a coating to the surface, its mechanical durability and its resistance to environmental effects. Because a coating is a thin layer, the results depend both on the material and on the QUALITY OF APPLICATION; the same paint gives an entirely different result over a different surface preparation.
This dual dependence is the most important knowledge in the field. A coating failure usually arises not from the paint itself but from the surface preparation: oil residue, insufficient roughening, an oxide layer or moisture. Coating tests therefore assess not only the product but also the process, and the results are used for process control.
COATING THICKNESS is a recurring variable in the field. Many durability results relate directly to thickness; a thin area becomes the starting point of corrosion. Thickness measurement is therefore reported routinely alongside the other tests and is usually taken at several points — thickness falls at edges and corners, especially on complex geometries.
Three approaches are used on the adhesion side, each giving different information. The tape test is fast and suitable for field use but is a coarse scale. The cross-cut test shows behaviour at the intersections of layers. The pull-off method produces a numerical strength value and is the most suitable for comparison.
On the mechanical side, flexibility (mandrel bending), impact resistance, hardness, abrasion and stone chip resistance are measured. Stone chipping has a special place in automotive: gravel striking the coating under real road conditions is simulated, and the result is assessed according to whether the coating continues to protect the base metal.
On the appearance side, gloss and colour difference are monitored NUMERICALLY. Colour is assessed with a colour measuring instrument rather than by eye and the colour difference is expressed as a number; this makes it possible to compare different lots and different suppliers.
On the durability side, accelerated ageing (xenon arc, fluorescent UV), humidity, condensation and salt spray are applied. The result is assessed with scales for blistering, rusting, creep from a scribe and loss of adhesion; these scales are defined in separate standards and the report must state which was used.
In industrial processes such as powder coating and electrophoretic coating, the curing cycle (temperature and time) is what determines the result. An under-cured coating looks good but has poor chemical resistance and adhesion; oven profile measurement is therefore part of coating quality control.
Method groups in this field
Thickness
Dry film thickness by magnetic and non-magnetic methods; multi-point measurement and assessment of the distribution.
Adhesion
Tape test, cross-cut test and pull-off adhesion strength.
Mechanical strength
Mandrel bend flexibility, rapid deformation (impact), pencil and scratch hardness, Taber abrasion, stone chipping.
Appearance
Gloss measurement, colour difference calculation, orange peel and surface defect assessment.
Environmental durability
Salt spray, humidity, condensation, xenon arc and fluorescent UV ageing, chemical and stain resistance.
Assessment scales
Scales for blistering, degree of rusting, creep from a scribe and loss of adhesion.
Commonly confused in this field
- A coating result depends on the surface preparation; even if the paint itself is good, a poor preparation gives a poor result.
- A durability result without a reported thickness cannot be compared.
- The tape test is a coarse scale; numerical comparison requires the pull-off method.
- Colour cannot be assessed by eye; numerical colour difference measurement is required.
- An ageing result without a stated assessment scale cannot be interpreted.
- If the curing cycle is incomplete the coating looks good but its durability is poor; the oven profile is part of quality control.
Which decisions these results support
- Paint system approval and supplier selection
- Process control of the paint line and lot acceptance
- Supporting outdoor and automotive durability claims
- Detecting defects arising from surface preparation
- Monitoring colour and gloss consistency lot by lot
Related Tests
Frequently Asked Questions About Adhesion
Is there a conversion between cross shear class and MPa value?
No. Cross cutting classifies the tendency of the coating to flake off from the cutting edges; Pull-out measures the breaking stress in the perpendicular direction. It is decisive which method the specification requires.