Gravelometer testing is a controlled impact test used to measure how well coatings resist debris damage. Its benefits include realistic debris simulation, repeatable results, and versatile testing conditions. It is commonly used in the automotive industry, but also has applications in the aerospace and construction industries.

What is Gravelometer Testing?

Gravelometer testing evaluates how well a coating withstands the impact of flying gravel and debris. This test simulates real-world damage in a controlled lab environment to measure coating chip resistance. It is widely used in the automotive industry to simulate the deterioration of car coatings.

This test is commonly applied to paint, clear coats or metallic plating that are expected to face road exposure. The coated test sample is mounted in a Gravelometer, and air pressure propels gravel at the surface. The resulting impact pattern is then compared to an original or standard sample.

Benefits and Drawbacks

The benefits and drawbacks of this test include:

Benefits

●     Realistic Debris Simulation: Replicates the type of stone and gravel impacts commonly experienced on roads and similar surfaces.

●     Repeatable Results: Applies a controlled level of impact to ensure reproducibility.

●     Versatile Testing Conditions: Can be performed under various laboratory-simulated environments to assess coating performance in different scenarios.

Drawbacks

●     Reliance on Visual Inspection: Assessment depends on visual evaluation, which can vary between observers. This is mitigated through proper training and standardized testing protocols.

Uses and Applications

This test is widely applied for quality control, material specification, and research. It is most commonly used in the automotive industry to specifically evaluate how vehicle coatings resist damage from road debris. The test ensures that coatings meet performance standards before vehicles reach the market.

Beyond automotive applications, this testing is also used in aerospace and construction industries to examine the resistance of coatings on equipment and other structures.

How is The Gravelometer Test Conducted?

This procedure follows a defined sequence so that impact force, debris type, and evaluation are consistent. Here’s a short summary:

1. The coated sample panel is secured on the rear side of the Gravelometer.
2. Controlled air pressure is applied, and a specific amount of gravel (E.g., 1 pint/approximately 300 pieces) is propelled toward the sample surface to create chipping damage.
3. After impact, the sample is removed and gently wiped with a clean cloth, then tape is applied and removed to pull away loose fragments.
4. The final condition of the sample is compared to standard transparencies, and visual examination is performed to determine a chipping rating based on the extent of damage.
5. Chipping ratings are expressed using letter-number combinations. The Point of Failure identifies the specific layer where the main damage has occurred. The Point of Failure is used when a more precise analysis is required.

Table 1 - Number of Chips

Table 2 - Size of Chips

Table 3 - Point of Failure

What Kind of Equipment Is Used to Perform This Test?

At ACT Test Panels, we use a Gravelometer machine that is designed specifically for controlled debris impact. 

The stone feed rate is regulated by an electromagnetic vibrating feeder, and compressed air is stored in a high-capacity reservoir to maintain constant flow and pressure during every test. The spray gun pressure can be precisely adjusted using a regulating valve. The spray gun can also be swapped out quickly if needed.

In addition to that, the system incorporates a multi-function display that reads pressure, test time, vibration frequency, and total impact count.

Table 4 - Equipment Specifications

Test Methods

Test methods include:

●     ASTM D3170

●     Ford BI 157-06 (Deviation: SAE J400 Gravelometer)

●     GM 9508P (Superseded 08/01/10)

●     GMW14700

●     SAE J400

Contact ACT Test Panels for All Your Testing Needs

ACT Test Panels has supported the global coatings industry since 1981 with reliable and reproducible test panels and objective third-party testing services. Gravelometer testing is one of many performance evaluations offered, and is conducted in an ISO17025-accredited laboratory by a team of experts committed to delivering test results on time.

Contact us today to get a custom quote or explore our test panels.

Frequently Asked Questions

Below are some of the most common questions related to Gravelometer testing.

How Much Does Gravelometer Testing Cost?

Pricing varies based on specific testing requirements. Request a quote so that accurate pricing can be provided based on the exact scope of your needs.

How are Results Evaluated?

The appearance of the impacted surface is compared to standard transparencies, and a visual evaluation is used to determine a chipping rating. Chipping ratings are expressed as letter-number combinations. 

The letter designates the size range of the chips being counted, and the number designates the quantity of chips. For example, “C5” indicates 3-6 mm / 25-49 chips.

In addition to that, Point of Failure is used to indicate the coating layer where the most predominant chipping failures are occurring. For example, “T” means Topcoat.

What is a Gravelometer Used For?

A Gravelometer is used to evaluate the resistance of coatings to impact from gravel or other debris. It simulates real-world conditions where surfaces, particularly on vehicles or equipment, are exposed to fast-moving particles, allowing manufacturers and researchers to measure surface damage. The results help assess coating durability, support quality control, and inform product development.