Silicone rubber is widely used for seals, gaskets, O-rings, flexible components, protective covers and specialist equipment because of its flexibility, temperature resistance and durability. Unfortunately, those same material properties can make silicone notoriously difficult to glue.
If you’ve tried applying a conventional adhesive to silicone and found that it simply peels away, the adhesive isn’t necessarily at fault. Silicone has a very low surface energy, which means many adhesives struggle to properly wet and grip the surface.
So, how do you bond silicone reliably?
One solution is to use a specialist silicone adhesive. However, where a fast-curing industrial bond is required, another option is a suitable Permabond cyanoacrylate adhesive used in conjunction with Permabond POP Primer.
In this guide, we’ll explain how to bond silicone, why POP Primer is important, and compare three Permabond options:
- Permabond 105 + POP Primer
- Permabond 751 + POP Primer
- Permabond 2050 + POP Primer
Knowing how to bond silicone correctly starts with understanding why conventional adhesives often struggle to achieve reliable adhesion to its low-energy surface.
Why Is Silicone So Difficult to Bond?
Silicone is an elastomer with an extremely low-energy surface. An adhesive applied directly to untreated silicone may appear to stick initially but achieve relatively little true adhesion.
This is why choosing an adhesive simply because it says “suitable for rubber” can cause problems.
Silicone rubber isn’t the same as EPDM, nitrile, neoprene or natural rubber, and an adhesive that performs extremely well on one rubber may perform poorly on silicone.
If you’re unsure which type of rubber you’re working with, see our Strongest Glue for Rubber UK Guide for a broader comparison of rubber bonding options.
For silicone specifically, Permabond recommends priming the silicone with Permabond POP Polyolefin Primer before applying a suitable Permabond cyanoacrylate adhesive.
You can also read Permabond’s guide to bonding silicone for further technical information directly from the manufacturer.
Why Do You Need Permabond POP Primer?
When considering how to bond silicone, surface preparation is just as important as the adhesive itself.
Permabond POP is an adhesion promoter developed for difficult, low-surface-energy materials including:
- Silicone
- Polypropylene (PP)
- Polyethylene (PE)
- PTFE
- Other fluoropolymers
On silicone, POP prepares the surface so that a Permabond cyanoacrylate can achieve substantially better adhesion than it would on untreated silicone.
POP Primer is applied to the silicone first. It is not mixed into the adhesive.
Surfaces should be clean, dry and free from grease or contamination. Permabond recommends cleaning silicone with isopropanol to help remove release agents before applying POP. Apply the primer to the silicone surface and allow it to dry before applying the selected cyanoacrylate.
Does POP Primer Affect Flexibility?
Yes, and this is an important consideration that can easily be overlooked.
While POP dramatically improves adhesion to silicone, using POP can reduce the flexibility and elongation of the cured adhesive system.
The exact reduction will depend on the materials, adhesive and application. In discussions with Permabond Technical regarding a highly flexible silicone application, they advised that a reduction in elongation of approximately 30% could be anticipated.
This doesn’t automatically make the adhesive unsuitable. Instead, it means you need to select an adhesive with enough flexibility in reserve for the finished application.
This is one of the reasons we offer several different options for silicone rather than recommending one adhesive for every job.
Option 1: Permabond 105 + POP Primer
Buy Permabond 105 Cyanoacrylate Adhesive
Permabond 105 is a low-viscosity, high-purity cyanoacrylate designed for fast bonding of plastics and elastomers.
It is an excellent choice when how to bond silicone really means “how do I achieve a very strong, fast bond between two close-fitting components?”
Permabond 105 offers excellent bond strength, but it isn’t designed to provide the high levels of elongation offered by products such as Permabond 751.
Best applications for Permabond 105 + POP
Consider 105 when bonding:
- Small silicone components
- Close-fitting silicone parts
- Silicone to rigid components
- Components where movement is minimal
- Small seals or components where maximum bond strength is more important than elongation
- Fast production assemblies
Its low viscosity also makes 105 particularly well suited to tight-fitting joints where a thick adhesive would be undesirable.
When NOT to choose 105
We wouldn’t make 105 our first choice for a silicone component that is expected to stretch significantly, repeatedly flex or undergo substantial movement.
For example, a highly flexible silicone glove, membrane or component that is regularly stretched may benefit considerably more from 751.
Think of 105 as the strength-focused option of the three.
Option 2: Permabond 751 + POP Primer
Buy Permabond 751 Flexible Cyanoacrylate 20GM
If flexibility is the priority, Permabond 751 is the standout option.
Permabond 751 is a flexible cyanoacrylate offering approximately 150% elongation before considering the effect of POP Primer. More importantly, it has been developed to maintain high elasticity over time.
This makes 751 particularly interesting when researching how to bond silicone components that don’t simply sit still after assembly.
Why is durable elongation important?
Some adhesives described as “flexible” can gradually lose flexibility as the adhesive ages.
For a component that is repeatedly stretched, compressed or flexed, initial flexibility isn’t enough. You want the bond to retain useful flexibility throughout its service life.
This is where Permabond 751 becomes particularly attractive.
Permabond Technical has advised us that when 751 is used with POP on silicone, an approximate 30% reduction in elongation could be anticipated.
That could take the adhesive from approximately 150% elongation to around 100% elongation.
Although reduced, this is still an exceptionally useful level of elongation for a cyanoacrylate adhesive.
Best applications for Permabond 751 + POP
We would consider 751 for applications including:
- Flexible silicone components
- Silicone gloves and flexible equipment
- Components subjected to repeated stretching
- Flexible seals
- Silicone parts exposed to movement
- Dissimilar materials where movement occurs
- Components subjected to vibration
- Applications involving repeated compression or flexing
When NOT to choose 751
751 isn’t automatically the right answer simply because you’re bonding silicone.
If you’re bonding two tiny, rigid, extremely close-fitting silicone components and flexibility isn’t required, the additional elongation offered by 751 may provide little practical benefit. In that situation, 105 + POP may be the simpler choice.
Likewise, don’t assume 751 turns a cyanoacrylate joint into a thick flexible sealant. If you need a large-gap, highly elastic seal or a substantial bead of adhesive, a specialist silicone adhesive or sealant may be more appropriate.
Option 3: Permabond 2050 + POP Primer
Buy Permabond 2050 Flexible Cyanoacrylate 20GM
Permabond 2050 sits nicely between the other two options.
It is a toughened, flexible cyanoacrylate offering good resistance to impact, vibration and peel. Permabond specifically identifies 2050 as an option for bonding silicone when used with POP Primer.
This makes it an excellent general-purpose choice where some flexibility is needed but the extreme elongation characteristics of 751 aren’t necessary.
Best applications for Permabond 2050 + POP
Consider 2050 for:
- Silicone O-rings
- Silicone seals
- Gaskets
- Flexible or semi-porous components
- Silicone parts exposed to vibration
- Silicone-to-dissimilar-material bonding
- Applications requiring improved peel and impact resistance
Permabond particularly highlights 2050 for soft seals and O-rings because it provides a less rigid joint than a conventional cyanoacrylate.
When NOT to choose 2050
For an application involving very high repeated elongation, we’d look at 751 first.
Conversely, where virtually no flexibility is required and the priority is simply a very fast, strong bond between close-fitting parts, 105 may be sufficient.
2050 is therefore the middle-ground option: good strength combined with useful toughening and flexibility.
How to Bond Silicone: 105 vs 751 vs 2050, Which Should You Choose?
| Adhesive | Main Advantage | Flexibility | Best Used For |
|---|---|---|---|
| Permabond 105 + POP | Excellent strength and fast cure | Low | Small, close-fitting silicone components with minimal movement |
| Permabond 751 + POP | High, durable elongation | Very High | Silicone that repeatedly stretches, flexes or moves |
| Permabond 2050 + POP | Toughened and flexible | Good | O-rings, seals, gaskets, vibration and general flexible bonding |
There isn’t a universal “best” silicone adhesive. The correct product depends on what the bonded component needs to do afterwards. The best approach to how to bond silicone will therefore vary depending on whether the application requires maximum strength, high elongation or a balance of both.
How to Bond Silicone: Step-by-Step
Once you’ve selected the correct adhesive, the basic process is straightforward:
- Identify the material. Make sure you’re actually bonding silicone rather than EPDM, neoprene, nitrile or another rubber.
- Clean the silicone. Remove grease, dirt and mould-release agents. Isopropanol is recommended by Permabond for silicone surface preparation.
- Allow the surface to dry completely.
- Apply Permabond POP Primer to the silicone surface.
- Allow the POP Primer to dry. At approximately 23°C, the Permabond TDS gives a typical drying time of around 30 seconds.
- Apply your selected Permabond cyanoacrylate sparingly.
- Bring the components together and correctly align them.
- Hold the components securely until sufficient handling strength has developed.
- Allow the adhesive to fully cure before placing the joint into service. Permabond recommends allowing 24 hours at 23°C for maximum bond strength.
With cyanoacrylates, more adhesive doesn’t necessarily mean a stronger bond. These products generally perform best as a thin adhesive film between well-fitting components.
When Should You NOT Use This System?
Understanding how to bond silicone also means recognising when a cyanoacrylate + POP system isn’t the right solution.
We wouldn’t automatically recommend these products for:
- Very large bonding areas
- Large or uneven gaps
- Applications requiring a thick flexible bead
- Joints where the adhesive itself must act as a substantial waterproof seal
- Applications requiring extreme continuous extension beyond the adhesive’s capability
- Unknown substrates where silicone hasn’t been confirmed
- Safety-critical applications without prior testing
- Applications exposed to chemicals or temperatures outside the adhesive’s specified resistance
If you’re actually bonding EPDM, natural rubber, nitrile or another rubber rather than silicone, you may not require POP Primer at all.
Our guide to choosing the strongest glue for rubber covers other rubber types and adhesive technologies in more detail.
For rubber-to-metal applications, you may also find our Best Adhesive for Rubber to Metal guide useful.
Always Test Before Full Production
Silicone formulations vary considerably. Additives, mould-release agents, surface contamination and the exact grade of silicone can all affect adhesive performance.
For this reason, we recommend carrying out a trial using the actual production materials before committing to a full application.
This is particularly important where the finished component will be exposed to repeated stretching, water immersion, chemicals, temperature cycling or significant mechanical loads.
Need Help Choosing an Adhesive for Silicone?
If you’re still unsure how to bond silicone for your particular application, contact Adhesive Supply Company with as much information as possible about:
- The exact materials being bonded
- Approximate bond dimensions
- Whether the joint needs to stretch or flex
- Temperature range
- Water or chemical exposure
- Loads acting on the joint
- Required cure or fixture time
For many silicone bonding applications, Permabond POP Primer combined with 105, 751 or 2050 provides a fast and practical solution. The key is choosing the cyanoacrylate whose mechanical properties best match the finished component.
For a rigid, close-fitting joint, start by considering 105 + POP. For maximum durable elongation, consider 751 + POP. For a balance of strength, toughening and flexibility, 2050 + POP may be the better choice.
Products Mentioned
- Permabond POP Primer 50ml
- Permabond 105 Cyanoacrylate Adhesive
- Permabond 751 Flexible Cyanoacrylate
- Permabond 2050 Flexible Cyanoacrylate
Always refer to the relevant Technical Data Sheet and Safety Data Sheet before use. Adhesive performance can vary according to substrate grade, surface preparation, joint design and service conditions. Testing on the actual materials is recommended before production use.