Gravelometer — SAE J400 / ASTM D3170 / ISO 20567-1

What Is Gravelometer?

Gravel impact test, in which the coated panel is bombarded with standard gravel grains launched with compressed air; It is a test in which the resulting peeling and dents are graded according to standard comparison tables.

Purpose of Gravelometer

The aim is to evaluate the resistance of vehicle exterior coatings against stones splashed from the road.

Which Products Is Gravelometer Applied To?

Automotive exterior paint systems
Stone impact protective coatings (PVC)
Rim and underbody coverings
Coated exterior trim parts

In Which Sectors Is Gravelometer Used?

AutomotiveMetalConstructionMachinery

Standards Related to Gravelometer

SAE J400
ASTM D3170
ISO 20567-1
OEM specifications (VDA, GMW, WSS)

Gravelometer Conditions

Gravel: Calibrated gravel of size and quantity defined in the standard
Pressure: Standard defined air pressure
Temperature: Defined in the specification; can be applied at low temperature (e.g. −20 °C)
Assessment: Rating according to standard comparison tables (e.g. SAE J400 scale)

Equipment for Gravelometer

Gravelometer tester
Calibrated gravel stock and sieve set
cooling cabinet
Standard comparison tables and viewing

Sample Requirements for Gravelometer

Panel covering system and thickness must comply with the specification
Gravel size distribution should be verified by sieving
The panel must be balanced at the test temperature
Loose coating should be removed with tape before grading

Duration of Gravelometer

Typically 2–4 days.

Gravelometer Procedure

1The panel is conditioned and cooled if necessary.
2Gravel size is verified.
3Gravel bombardment is applied at defined pressure.
4Panel bantla temizlenir.
5Hasar standart tablolarla derecelendirilir.
6The results and photos are reported.

Gravelometer Acceptance Criteria

The acceptance criterion is the minimum rating given in the OEM specification.

Evaluation of Results

At low temperature, coatings become brittle and the result deteriorates significantly; Without reporting the temperature the result cannot be compared. Gravel size distribution changes with fracture over time and should be verified by sieving.

Gravelometer Report

Applied standard and OEM specification
Coating system and thicknesses
Gravel size and pressure
Test temperature
Rating and photos

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 authorisations

Related Regulations

Automotive OEM paint specifications

Paint and Coating Testing — What Does This Testing Field Cover?

The section below describes the field that the Gravelometer 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 Gravelometer

According to which standard is Gravelometer made?

Gravelometer is executed in scope SAE J400, ASTM D3170, ISO 20567-1 and OEM specifications (VDA, GMW, WSS). The limit values and acceptance criteria to be applied are defined in the product standard; The version valid for your product is confirmed in writing at the offer stage.

Which products does Gravelometer apply to?

Mainly applied to Automotive exterior paint systems, Stone impact protective coatings (PVC), Rim and underbody coverings and Coated exterior trim parts. Whether your product is included in the scope is determined by examining its technical specifications and intended use.

Under what conditions is Gravelometer done?

The determining parameters are: Gravel — Calibrated gravel of size and quantity defined in the standard, Pressure — Standard defined air pressure and Temperature — Defined in the specification; can be applied at low temperature (e.g. −20 °C). The full terms are in the "Test Conditions" section on the page and vary depending on the product standard.

What kind of sample is needed for Gravelometer?

Panel covering system and thickness must comply with the specification, Gravel size distribution should be verified by sieving and The panel must be balanced at the test temperature. The number of samples is determined according to the product standard and the scope to be reported.

How long does Gravelometer take?

Typically 2–4 days. This duration belongs to the experiment itself; sample preparation, queuing and reporting are also evaluated. A realistic schedule for your product is given in the offer.

What is the Gravelometer result called "appropriate"?

The acceptance criterion is the minimum rating given in the OEM specification.