When to Use Epoxy vs. Super Glue and Other Adhesives

You’ve probably heard the saying: “If it moves and shouldn’t, use duct tape.” It’s funny, but it also works … sometimes. The not-so-funny part is that when it doesn’t work, it fails miserably. When it comes to sticking things together, there are many adhesive options for various materials and levels of stress. How do they compare? Epoxy vs. super glue (cyanoacrylate) or room temperature vulcanizing (RTV) silicone, for example, all have their own best — and worst — uses.

The Two Types of Adhesives

Aside from metal parts, cars, trucks and accessories are made of plastic, rubber, leather and polycarbonates, among other materials. When a component becomes dislodged, replacement is a good solution, but sometimes you need a faster solution until you can get to the repair shop. Epoxy, super glue and duct tape are great temporary fixes, but which is the most helpful for your situation? The keys to understanding whether to use epoxy vs. super glue or silicone vs. urethane are compatibility and application.

There are two types of adhesives. Epoxy, super glue, urethane, polyurethane and silicone are reactive adhesives, curing chemically. Construction adhesive and contact cement, on the other hand, are “non-reactive” adhesives, curing by evaporation. Upon evaporation of the solvent, the remaining adhesive bonds the parts.

Different adhesives also have further nuances in their chemical processes. For example, two-part adhesives start curing when the two parts are mixed together, bonding the parts. Conversely, one-part adhesives, such as super glue and silicone, react on exposure to ultraviolet (UV) light, heat or moisture.

Epoxy vs. Super Glue on Different Materials

To get the most out of your repair, match your adhesive choice to the material you’re working with. Here’s a quick guide:

• Epoxy: metal, rubber, glass, plastic, fiberglass and fiberglass-reinforced plastic (FRP)
• Acrylic: metal, rubber, glass, plastic, fiberglass, FRP and polycarbonate (PC)
• Urethane: metal, rubber, polyvinyl chloride (PVC), glass, plastic, fiberglass, FRP and PC
• Polyurethane: metal, rubber, fabric, leather and canvas
• Cyanoacrylate: metal, plastic, fabric, leather and canvas
• Silicone: metal, rubber, glass, canvas, fiberglass and FRP
• Contact cement: rubber, fabric, leather and canvas
• Construction adhesive: metal, fabric, leather and canvas

Note one caveat on repairs involving plastic: Most adhesives only work well with one plastic, such as acrylonitrile butadiene styrene (ABS) or polypropylene (PP). Choose a compatible adhesive for best results. For example, cyanoacrylate is not compatible with acrylic, ABS and some PE (polyethylene), PP and PC blends. The adhesive label will have more in-depth information.

Always Read the Instructions

Having matched the adhesive with your material, it’s time to consider the application, strength required and exposure.

• Epoxy is the strongest of the reactive adhesives and is resistant to high temperatures, solvents, UV light and impact. Epoxy cures in two to 60 minutes (longer is stronger), reaching full strength in 24 hours.
• Acrylic requires less surface preparation than epoxy, but is weaker. It cures in three to 20 minutes, taking up to 48 hours to reach full strength.
• Silicone cures in the presence of humidity, hardening in 20 to 40 minutes and gaining full strength in one to three days. It works best as a sealant between two components, such as in form-in-place gasket (FIPG) applications.
• Urethane adhesive is strong and elastic. It’s best used to bond and seal modern automotive windshields. It’s impact-resistant, taking up to two hours to cure and up to a week for full strength.
• Cyanoacrylate is fast and strong, but brittle. It’s best used in exact-fit applications, such as cracked plastics or metal, where capillary action can draw the adhesive into the repair. It’s usually the best choice to bond small, low-stress and nonmoving parts.
• Construction adhesive is a strong, slightly flexible adhesive, taking 10 to 30 minutes to dry and 12 to 24 hours to cure to full strength. It’s also highly resistant to temperature changes, water and chemicals.

Before you begin application, make sure your work area is clear of anything that could be damaged by coming into contact with the adhesive. Also make sure to read the instructions thoroughly, even if they seem obvious. Every product will have a slightly different process.

Remember to always use the right adhesive for the job at hand, and save the duct tape for temporary repairs!

Check out all the chemical products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on finding the right adhesive for your repair job, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Flickr.