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Bonding Signs with Porous and Non-Porous Substrates

( 04/21/2021 ) Written by: Kimberly Richardson

Contemporary designers often mix materials to lend their designs a sense of contrast and complexity. Accomplishing this look in signage requires joining dissimilar elements, including metal, wood, slate, stone, concrete, granite, glass and more. For a smooth, unblemished look, designers often want to avoid the use of mechanical fasteners, choosing to bond sign elements using adhesives instead.

Strong bonds can be achieved using adhesives—the key is to select the appropriate product for a given substrate. Some substrates, such as concrete, are porous; some, such as glass, are nonporous; some, like certain kinds of stone, may have an uneven or bumpy contact area. We offer two high-performing adhesive options, each with a work time of 20-40 minutes, that address all of these surface conditions.

LORD 7610DTM is a one-part, bright white, general purpose adhesive/sealer for bonding bare metal and a wide variety of materials, including natural materials like stone. LORD 7610DTM is soft and flexible as it is being dispensed and it maintains much of that softness and flexibility throughout the life of the product. It is a moisture-cure material that takes approximately 24 hours to set. LORD 7610DTM offers indirect UV resistance and lap shear tests show about 500 psi of strength for metal bonding.

LORD 320/322 is a two-part epoxy, high viscosity, grey adhesive for bonding metals, SMC, fiberglass and natural materials.  LORD 320/322 is formulated with rubber tougheners that give it excellent environmental and impact resistance. It is very hard after curing. Lap shear tests show over 1500 psi of strength for aluminum-to-aluminum bonding.

For signs that are large and/or heavy, LORD 320/322 will provide the strongest bond and may be the best product for the job. If the assembly might be subject to vandalism, LORD 320/322 will provide the best protection because its harder cured state makes it more difficult to pry apart.

Tips for Assembly
Surface preparation should include making sure the surfaces are clean, dry, and free of loose debris. Oil or grease should be removed with a mild organic solvent such as isopropyl alcohol. If the substrate is smooth, glossy or shiny, it should be primed with a glass primer (such as LORD AP-134) to provide a stronger bond. If the sign is to be located outdoors, the best long-term bond strength will be achieved if the metal is painted or primed (if using LORD 320/322). The product will, however, bond to bare metal.  

Adhesive strength is proportional to the amount of surface area covered. Therefore, it is best to maximize the area of adhesive application. After two substrates are assembled, apply even pressure to the entire surface, making sure there is full contact between the substrates and that the adhesive extends to the edge of the joined surfaces. It is recommended to apply a weight, fixture or clamp to the assembly to press both substrates together during handling time.

LORD 7610DTM is dispensed with a standard caulk gun. LORD 320/323 is dispensed with a gun for two-part adhesives and is available in 50 mL and 200 mL cartridges.

For more information on how adhesives can help create long-lasting signage—even for contemporary designs where dissimilar materials are combined—contact us today or learn more in our sign webinar series.

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