Whether you’re doing DIY projects or repairs around the house, knowing which adhesives work with different materials is crucial. Epoxy and silicone are popular options when bonding or sealing objects, but will epoxy actually stick to cured silicone?
The short answer is no, epoxy does not bond well to silicone. While epoxy can initially adhere to silicone, the bond will deteriorate over time resulting in a weak, unstable connection.
Read on to understand why epoxy and silicone don’t mix and what your alternatives are when fastening silicone materials together. With the right information, you can avoid adhesion issues and create long-lasting bonds for your projects.
Does epoxy stick to silicone?
No, epoxy resin does not stick to silicone. Epoxy is a two-part adhesive that forms when you mix epoxy resin and hardener. Epoxy sticks best to other plastics and metals, but it does not stick well to silicone.
Silicone is a resin itself, and other resins don’t stick to silicone. This makes silicone perfect for resin moulds. Silicone moulds are popular with DIY enthusiasts because they can be used to make small items like jewellery and coasters.
Other materials that epoxy resin does not stick to include:
- Parchment paper
- Painters tape
- Rubber
- Polyethylene (hot glue)
- Polypropylene
- Vinyl
- PTFE
What Are Epoxy and Silicone?
Epoxy is a two-part adhesive made up of an epoxy resin and a polyamine hardener. When mixed together, the epoxy cures to form a rigid, highly strong bond that is resistant to heat, chemicals, and moisture. Epoxies are ideal for bonding dissimilar materials like metal to plastic or glass to concrete.
Silicone is a polymeric sealant made up of siloxane and silanol. It has flexible and waterproof properties. Silicone is commonly used as a sealant in wet areas like bathrooms, kitchens, and plumbing applications. The silicone cures to form a rubber-like bond.
Why Doesn’t Epoxy Stick to Silicone?
There are a few reasons why epoxy does not bond well to silicone:
- Low surface energy – Silicone has an inherently low surface energy which makes it difficult for other adhesives like epoxy to bond to it. The epoxy simply beads up and pulls away when cured.
- Flexible vs. rigid – Epoxy cures to a hard, inflexible bond while silicone remains flexible. The differing properties make it nearly impossible for epoxy to maintain a long-lasting bond.
- Non-porous – Epoxy adheres best to surfaces that are porous and allow the epoxy to seep in. The non-porous surface of cured silicone prevents epoxy from soaking in and creating a strong mechanical bond.
- Release agents – Some silicones have release agents built into their chemistry. These release agents allow the silicone to be easily removed from surfaces after curing. They also prevent adhesion to other materials like epoxy.
How to Make Epoxy Stick to Silicone
While epoxy does not bond well directly to silicone, there are a few tricks to get the two to bond:
- Mechanically abrade – Use sandpaper or a wire brush to rough up the surface of the cured silicone. This gives the epoxy something to mechanically adhere to.
- Use a primer – An epoxy primer applied first can help the epoxy bite into the silicone. Primers containing isocyanates have the best effect.
- Apply an intermediary – Coat the silicone first with a layer of cyanoacrylate glue or spray adhesive before applying the epoxy. The epoxy bonds to the glue rather than directly to the silicon.
- Replace silicone – If possible, remove the existing silicone entirely and replace it with a non-silicone material the epoxy can easily bond to.
With the right preparation and methods, it is possible to get epoxy to form a lasting bond with silicone. Be sure to test adhesion and allow proper curing time before relying on the bond for any structural applications.
How to Make Epoxy Stick to Silicone
Epoxy and silicone generally do not bond well together. However, with the right preparation and application, you can get epoxy to form a lasting bond with silicone. Here are some tips:
Clean the Surfaces
The first step is to clean both the silicone and epoxy bonding surfaces. Use isopropyl alcohol to remove any oils, dust, or debris. Lightly sanding the silicone with fine-grit sandpaper will also help remove any gloss and expose a fresh surface. Proper cleaning and abrasion give the epoxy something to mechanically adhere to.
Use a Primer
After cleaning, apply a primer to the silicone. Primers that contain isocyanates like silane or urethane work best. Allow the primer to fully cure per the manufacturer’s instructions before applying the epoxy. The primer gives the silicone some surface chemistry for the epoxy to bond with.
Use a High-Strength Epoxy
For best results, use a high-strength or structural epoxy rather than a standard craft epoxy. The stronger epoxy formulations have superior adhesion properties. They are better suited for bonding dissimilar materials like silicone.
Apply the Epoxy in Thin Layers
Apply several thin coats of epoxy rather than one thick layer. Spread the epoxy on with a disposable brush or applicator. Allow each thin layer to partially cure before adding the next. Thin applications help prevent air bubbles and result in maximum adhesion.
Clamp the Pieces Together
Once assembled, clamp the parts tightly together as the epoxy cures fully. This helps force the epoxy into the silicone for a better mechanical bond. Use just enough clamping pressure to squeeze out excess epoxy and eliminate any gaps between the surfaces.
Allow the Epoxy to Cure Completely
It is critical to allow the full epoxy cure time recommended by the manufacturer, which is usually 24-72 hours at room temperature. The epoxy must be allowed to fully harden and build strength before putting any stress on the silicone bond.
Following these tips will allow you to successfully adhere epoxy to silicone for repairs and projects. Just be sure to test a small area first and allow ample cure time before relying on the bond for any structural loads.
FAQs
What Type of Epoxy Should I Use to Adhere Silicone?
use a two-part epoxy designed for bonding and structural applications. These high-strength epoxies have superior adhesion properties compared to standard craft epoxy.
How Long Does It Take for Epoxy to Cure on Silicone?
Allow 24-72 hours for the epoxy to fully cure when bonding to silicone. The exact cure time depends on the specific epoxy used.
What If the Epoxy Does Not Stick to the Silicone?
If the epoxy is not bonding, try lightly sanding the silicone and wiping it with alcohol prior to epoxy application. Also, ensure you are using a high-quality structural epoxy and applying it in thin coats.
Can I Use Epoxy to Repair a Silicone Product?
Yes, epoxy can be used to repair or mend silicone products like bakeware, moulds, and seals. Properly prepare the silicone and allow full cure time before stressing the repair.
Can I Use Epoxy to Make a Mold of a Silicone Object?
You can make an epoxy mold from a silicone object. Apply a release agent like PVA to the silicone before laying up the epoxy over it to create the mold.
conclusion
While epoxy does not naturally bond to silicone, with the right preparation and application techniques, a lasting epoxy-silicone bond can be achieved. The key factors for success are:
- Properly cleaning and abrading the silicone to improve mechanical adhesion
- Applying a primer containing silane or urethane to the silicone
- Using a high-strength, two-part epoxy designed for structural bonding
- Building up multiple thin coats of epoxy rather than one thick layer
- Allowing the full epoxy cure time before stressing the bond
By following these best practices, you can overcome the challenges of joining epoxy and silicone. Test a small area first and be patient with cure times. A durable epoxy-silicone bond opens up new possibilities for repairs and material bonding.
We hope this article has helped explain why epoxy and silicone do not naturally bond and provided useful tips for joining them successfully. please share this article if you found it helpful!
