By Emily Newton editor-in-chief of Revolutionized Magazine

A careful and thoughtful approach to selecting an adhesive for rubber bonding will avoid unintend-ed consequences and less-than-ideal results.

How to Find the Best Rubber Adhesive

A careful and thoughtful approach to selecting an adhesive for rubber bonding will avoid unintended consequences and less-than-ideal results.

Finding the best rubber adhesive requires thinking of various factors and needs associated with your product. However, taking a careful and thoughtful approach reduces the chance of making errors or experiencing unintended consequences. Here’s a closer look at how to find the best adhesive for rubber bonding.

Know the Conditions

A good starting point is to think about the conditions the rubber will go through after bonding. It’s then easier to narrow down the options for adhesives by eliminating unsuitable options. Maybe you require an adhesive to prepare waterproof footwear for outdoor activities. Then, the chosen product must remain reliable when exposed to excessive moisture, including short-term submersion. On the other hand, you might need an adhesive for a rubber product primarily used outside and exposed to frequent sunlight. If so, it must withstand ultraviolet light.

People also believe adhesive bonding will eventually replace the welding used on medical device joints. UV adhesives and cyanoacrylates are popular options in such cases. However, when bonding rubber for a medical device, people must consider the product’s uses. For example, will the bonded rubber be in direct contact with the body or skin? Must the rubber withstand exposure to bodily fluids or disinfecting products or procedures? Is the product a single-use item or reusable? What regulatory requirements must the manufacturer satisfy to ensure safety?

Some rubber-containing products have dedicated adhesives for fixing them. A wetsuit is one example. The neoprene and rubber are the parts of a wetsuit most likely to tear. An avid surfer or sea swimmer who goes in the water 100 times annually may need to replace their wetsuit every two years. However, that’s less likely if they know how to repair them. Wetsuit cement is the proper adhesive to handle rubber-related damage. The general process is to apply wetsuit cement to both sides of the seam and let it dry before sewing it by hand. Then, apply a final coat for reinforcement. When you consider that wetsuits get used in both wet and salty conditions, it makes sense that manufacturers have a specific adhesive for that application.

Verify the Rubber

Another thing to find out before choosing an adhesive is the kind of rubber used in the product or application. Natural rubber comes from nature – specifically, certain types of trees. Most of the world’s natural rubber comes from Thailand, although other Asian countries have recently increased production. Natural rubber is a common material used for high-performance tires due in part to its strength and heat-resistant nature. It’s also a component in many adhesives. That’s because the sap used to make natural rubber has a stickiness and tacky consistency. Cyanoacrylate adhesive is one of the best options to consider when working with natural rubber. People often recognize it under its commercial name: Super Glue.

In contrast, you can also find synthetic rubbers that typically come from petroleum byproducts. Approximately two-thirds of the rubbers produced annually in the United States are in this category. Ethylene propylene diene monomer (EPDM) is a widely used type of synthetic rubber. However, it – along with some other types of synthetic rubber – can pose challenges when working with adhesives. That’s because they have non-porous, smooth surfaces that could resist proper adherence to the chosen product. A practical way around that issue is to choose two-part acrylic glue. Users purchase these products separately, then mix them before application. They offer more stability and a longer shelf life than premixed adhesives. Many of these adhesives are epoxies that tolerate abrasion and weather well.

You’ll have the most limitations when finding an adhesive for rubber bonding if working with silicone rubber. That’s because silicon-based products and cyanoacrylate adhesives are typically the only options. Plus, you’ll usually need to coat the surface with a primer first.

Choosing Cyanoacrylate

There will almost certainly be instances when you need a rubber adhesive but are unsure of the type of material that requires bonding. Cyanoacrylate is usually the best option in such cases for several reasons:

• It cures quickly
• It works in small amounts
• It’s readily available

You’ll usually know within minutes whether the adhesive will bond to the rubber if expected. Plus, it’s often only necessary to apply the product in drops or thin lines. Finally, since most hardware stores have this type of adhesive, you can probably find it locally and for a reasonable price.

If experiments show you that the cyanoacrylate won’t hold, you can then move on to more specialized adhesives. Some of those are cyanoacrylates that require adding primers to the surface first.

Suit the Complementing Material

Using the proper adhesive for rubber requires knowing how other materials fit into the project, if applicable. Perhaps you’re just bonding rubber to rubber. If so, the tips above about using a product made for bonding certain types of rubber will steer you in the right direction.

However, working with rubber and other substrates can bring specific challenges. That’s partially because the rubber or other material may have different coefficients of thermal expansion (CTE). Such a situation occurs when finding a rubber adhesive that will bond the material to metal, for example.

One workaround is to select an adhesive with as low a CTE as possible. However, bear in mind that such adhesives tend to be stiffer than those with a higher CTE. Another possibility is to choose a flexible, low-modulus adhesive for working with the two substrates. They provide a toughened cure that’s often preferable for some applications, including those where one of the goals is to reduce stress on the joint.

Get Manufacturer’s Information

Your project’s scope and purpose may not allow for much trial and error. In such cases, the best thing to do is rely on relevant and easily accessible information. Start by looking for details on the adhesive’s packaging. It will usually state the kinds of materials the product does or does not work well with.

The product’s external package or insert is also usually an excellent source of information for specifics like cure time, application tips, and what to do if mishaps occur. Plus, the materials will probably have a website, phone number, or both. Those are your next resources to try if the provided content doesn’t answer all your questions.

Maybe you’re thinking of ordering a highly specialized and pricey rubber adhesive and using it on a material for the first time. That’s a situation where you can probably get the most appropriate answers by contacting the manufacturer directly. Speak to a sales representative about your specific needs and concerns to get peace of mind about what to do next. The company employee may evaluate your situation and determine there’s a better adhesive available than the one you previously considered. Alternatively, they’ll confirm that the one you planned to buy is the optimal choice or admit that none of the adhesives in the company’s inventory match your needs.

Select with Care

You’ve almost certainly heard stories of people assuming they got the right rubber adhesive without considering the product itself or their specific requirements. Maybe you’ve made that mistake a few times, too. It takes time and effort to shop carefully for a rubber adhesive. However, doing so is one of the most practical ways to get the results you expect.