EP40: Structural Epoxy Used for Steel Bonding in Marine Applications

April 1, 2026

Master Bond Inc., Hackensack, NJ

Figure 1. (left) An aluminum mold was used to ensure the correct dimensions of the adhesive singlelap joint according to ASTM D1002. Before applying EP40, the naval steel specimens (dark grey) were cleaned with acetone. (right) EP40 was cured at room temperature for more than 72 hours by applying a pressure of 2 MPa using metal blocks.

To reduce its environmental impact and pollution, the shipping industry is investigating methods to construct more lightweight ships. One potential method is using adhesive bonding techniques to replace traditional welding and riveted joints on ships to fabricate lighter ships with smaller carbon footprints. However, adhesives age and deteriorate when exposed to moisture, high temperatures, and ultraviolet light. This makes it necessary to understand how they age in maritime environments to determine whether they can truly replace traditional welding techniques.

Figure 2. Comparison of the average shear stress-strain at different temperatures, including a photo of a test specimen bonded by EP40 (from Rodríguez-Dopico et al.).

To this end, researchers at Centro de Investigación en Tecnologías Navales e Industriales (CITENI) and Centro de Investigación TIC (CITIC) developed a new method for studying adhesive aging on naval steel substrates. Master Bond EP40 was selected as the test adhesive for this method due to its strong performance and suitability for marine conditions. By using EP40, the team ensured that the observed adhesive bonding behavior would reflect a high-quality epoxy’s potential in ship structures. The goal was to evaluate how EP40 bonds to naval steel and how the bulk epoxy material would behave in seawater to provide insights into the construction of lighter ships using this approach.

Key Parameters and Requirements

The authors first characterized EP40 and the adhesive joints formed with naval steel. They then subjected both the bonded joints and bulk epoxy samples to accelerated-aging tests in seawater to analyze how EP40’s properties changed. All bonding experiments were carried out using EP40, which allowed the researchers to use the same epoxy for multiple test configurations.

The tests included single-lap joint shear tests to measure the shear strength of EP40 bonding two steel pieces in an overlapping configuration, as well as tensile adhesive joint tests to measure the tensile strength of EP40 between steel substrates. The experiments also included bulk epoxy tests to measure the inherent mechanical and thermal properties of EP40 itself.

Single-Lap-Joint Shear Strength Test Specimen Preparation using EP40

Figure 3. Average strain–stress curve under tensile deformation, with the standard deviation shown by the gray error bars, as well as a representative tensile test specimen (from Rodríguez-Dopico et al.).

For the single-lap-joint shear strength tests, the authors used an aluminum mold to prepare naval steel specimens according to ASTM D1002, which were cleaned with acetone before applying EP40, as shown in Figure 1. The authors used a spacer to ensure a joint width of 0.1 mm and then cured EP40 by applying a pressure of 2 MPa for more than 72 hours at room temperature. The overlap adhesive bond dimensions were 12.7 mm in length and 25.4 mm in width, providing a total shear area of 322.6 mm2.

Tensile Test Specimen Preparation using EP40

Figure 4. (a) Comparison of experimental data and analytical model for constant loads of 0 percent and 6 percent of the tensile strength of joints bonded using EP40. (b) Stress-strain curves of dried and aged bulk specimens at different loads applied. Aging was conducted until complete saturation at room temperature for 312 h for the 0 percent load and 522 h for the 6 percent load (from Rodríguez-Dopico et al.).

For the tensile adhesion tests (ASTM D897 standard), a different specimen geometry was used. Two circular naval steel coupons were bonded in a buttjoint configuration to measure tensile pull-off strength. As with the lap joints, the steel surfaces were cleaned with acetone and prepared to ensure good bonding with EP40. A 1 mm thick spacer ring was placed between the steel disk faces to set a consistent adhesive layer thickness for the tensile specimen. EP40 was applied to the bonding area, and the assembly was clamped tightly, maintaining alignment during curing. The epoxy was again cured for 72 hours at room temperature under pressure from the clamping fixture. This produced a fully cured epoxy bond of 1 mm thickness joining the two steel disks. The use of EP40 in this configuration demonstrated its versatility in bonding different joint types, forming a strong adhesive interface across the bonded area.

Bulk Tensile Test Specimen Preparation using EP40

The authors also performed bulk adhesive tests before and after aging. To manufacture the specimens, they blended the two adhesive components in a 1:1 ratio and mixed them using a centrifuge machine. Due to the high viscosity of the blend, the authors manufactured the adhesive plates according to the French standard NF T 76-142, which involved inserting the adhesive into a mold, enclosing it in a 1-mm-thick silicone frame, and then curing EP40 at room temperature for more than 72 hours in the mold under a pressure of 2 MPa.

Conclusions

Overall, the newly developed testing methodology using EP40 as the model adhesive was effective for evaluating the performance of marine adhesives. EP40 played a central role in establishing this method, as its reliable performance allowed the authors to confidently interpret changes due to aging rather than dealing with inconsistent material behavior. The results from EP40 suggest that structural epoxy adhesives are viable options for marine bonding applications.

As part of their study, the authors showed that EP40 maintained a tensile strength above 4 MPa, even after being immersed in seawater for more than 500 hours under an applied load. If adhesives like EP40 can replace certain welded joints, they may enable the construction of lighter, more fuel-efficient ships that produce fewer emissions. The authors of the study concluded that the methodology developed with EP40 is applicable to all types of structural adhesives intended for marine environments, allowing future researchers to use this approach to evaluate other adhesive candidates.