Silicone rubber is used for a wide range of applications in many industries. Thanks to the uniquely rugged properties of silicone, it can perform for decades under conditions that would destroy most natural rubbers.

The properties that make silicone rubber impervious to damage also keep many sealants from sticking to it. If you need to seal a gap between one kind of material and a piece of silicone rubber, what kind of sealant should you choose? And what can you do to help them bond together?

Silicone rubber can be tricky to seal, but we can help!

What Is the Best Adhesive for Silicone Rubber?

Silicone rubber is a stable material made of oxygen and silicon atoms. This chemical structure makes silicone rubber impervious to water, chemicals, solvents, UV rays, extreme temperatures, physical pressure, acids, bases, and mild oils.

Sealing silicone rubber can be a nuisance. In fact, one of the only things that will stick to silicone rubber is a silicone-based sealant. To understand this better, we need to dig into the science of these substances.

What is RTV Silicone?

In order for a silicone sealant to stick to silicone rubber, it needs to be a high-quality, 100% RTV silicone. RTV silicone is a liquid or paste form that people usually apply as a glue or caulk. RTV stands for room temperature vulcanizing, which means the silicone reacts with moisture in the air to cure. It cures solid at room temperature, without extra heating, within 24-48 hours.

All of this is important because there are two different chemical formulations of RTV silicone sealant to choose from.

Acetoxy Silicone Sealants

Acid cure silicone uses acetic acid as its curing agent. The acetic acid off-gasses during the curing process and is responsible for the conveniently quick (but strong vinegary-smelling) cure of these acetoxy silicone sealants.

Acid cure silicone is typically used for creating waterproof, weatherproof, UV-resistant, temperature-resistant seals. It will adhere to most clean surfaces, and its flexible seals will not peel or crack. Acid cure silicone is a day-to-day necessity in industries such as construction, HVAC, automotive, and sheet metal assembly.

The big drawback of acetoxy silicone is that it's very corrosive to some metals, especially brass and copper. It also breaks down some plastics. The acetic acid makes this kind of silicone unsuitable for some jobs.

Neutral Cure Sealants

Neutral cure silicone uses alcohol as its curing agent. In this case, the sealant off gasses alcohol, which smells mild and inoffensive. This type of silicone takes a bit longer to cure completely.

Neutral cure silicone sealants have the same waterproof, weatherproof, UV-resistant, and temperature-resistant properties as acid cure does but will not corrode metals or other substrates. This makes it the best option for situations where high chemical resistance is important. Neutral cure silicone is also the only sealant that you can trust to adhere to and seal up silicone rubber, vinyl, and concrete.

RTV neutral cure silicone sealant is a go-to solution for more demanding or delicate conditions where acetic acid would cause damage. It excels at sealing electrical components, harsh chemical containment, medical equipment sealing, and outdoors on natural stone or exterior surfaces.

Does Silicone Stick to Rubber?

In short, yes. The only sealant that will stick to silicone is more silicone, and in almost any industrial setting, rubbers are synthetic silicone rubber.

Silicone rubber is used because it's:

• Nontoxic
• Extreme heat- and cold-resistant
• Chemical insulator
• Electrical insulator
• Waterproof
• Liquid and molds to any shape
• Ruggedly tough
• Flexible

You'll find silicone rubber used in almost any industry. From rubber gaskets to medical equipment to manufacturing facilities, you'll need to seal rubber items to other surfaces often. Neutral cure silicone is the correct rubber adhesive for the job.

Why Use Silicone Sealant?

Not only is silicone the only material that will adhere to silicone, but when a silicone seal cures fully, it offers the same qualities as the rubber it's sealing. A silicone seal will flex with the rubber and offer comparable water resistance, temperature tolerance, and rugged durability so the seals and rubber will offer consistent, leak-free coverage and protection for your project.

Tips for Getting A Strong Bond

If you work with silicone sealants and rubber, you know sealing them together is tricky at best and prep is everything.

Here are the basics:

• Make sure the surfaces you need to seal are totally clean and dry before sealing.
• Wipe them down with a rag soaked in denatured alcohol to clean away all oils – even fingerprints.
• Apply a smooth, even bead of silicone sealant, and do not smooth down flat.
• Press the surfaces together. Apply constant pressure to get the best adhesion between the sealant and the rubber.

You Can Rely On Our Neutral Cure Silicone

Silicone seals should stick and last. Finicky jobs like silicone rubber sealing demand the best 100% RTV neutral cure silicone sealant you can find, or they just won't hold up.

At Silicone Depot, we're here to help you avoid that frustration by offering top-shelf silicone sealants you can depend on when other sealants just won't stick. For help picking the right silicone adhesive for your next project, give us a call at 812-824-8000.