Difficult
How to glue Silicone rubber to Silicone rubber
The short answer
A flexible silicone adhesive or sealant is the best-supported starting point for Silicone rubber to Silicone rubber. Smooth-On Sil-Poxy has official documentation whose stated scope covers this joint at material-class or exact-substrate level. Prepare both faces as specified, maximise overlap, minimise peel and validate a representative coupon before critical use.
Why this bond behaves the way it does
A flexible silicone adhesive or sealant matches the joint's porosity, stiffness and gap needs better than the listed alternatives. The recommendation is graded B because official documentation supports the relevant substrate classes, while the exact production grades and joint geometry still need verification.
What to use
Best choice
Silicone sealant
Use a flexible silicone adhesive or sealant as the first route because the cited product and preparation documents cover the controlling substrate classes. This is strongly supported but still requires a coupon for the exact grades.
Primer: Use only the primer named for the selected silicone or cyanoacrylate system.
Gaps: Maintain the bond line stated by the manufacturer and do not clamp it dry.
Curing: Do not confuse initial grab or handling strength with full cure.
Watch out: Coupon-test the exact substrate grades and surface finish.
Also works
Cyanoacrylate
A primed cyanoacrylate is an alternative only when a current product document covers both actual faces, the bond-line thickness and the service environment.
Primer: Use only the primer named for the selected silicone or cyanoacrylate system.
Gaps: Use only on the thin, close-fitting joint stated by the exact grade.
Curing: Do not confuse initial grab or handling strength with full cure.
Watch out: Coupon-test the exact substrate grades and surface finish.
Also works
Two-part epoxy
A toughened two-part epoxy is an alternative only when a current product document covers both actual faces, the bond-line thickness and the service environment.
Primer: Use only the primer named for the selected silicone or cyanoacrylate system.
Gaps: Maintain the bond line stated by the manufacturer and do not clamp it dry.
Curing: Do not confuse initial grab or handling strength with full cure.
Watch out: Coupon-test the exact substrate grades and surface finish.
Avoid
Hot melt, hot glue
Avoid ordinary general-purpose adhesives on cured silicone. Its low-energy surface usually needs a silicone-specific adhesive or the exact primer and cyanoacrylate system named by the manufacturer.
Primer: Use only the primer named for the selected silicone or cyanoacrylate system.
Gaps: Maintain the bond line stated by the manufacturer and do not clamp it dry.
Curing: Do not confuse initial grab or handling strength with full cure.
Watch out: This avoidance is for the ordinary unqualified family, not a specialist grade with explicit manufacturer evidence.
What to avoid
Avoid ordinary general-purpose adhesives on cured silicone. Its low-energy surface usually needs a silicone-specific adhesive or the exact primer and cyanoacrylate system named by the manufacturer.
Preparing the surfaces
Silicone rubber
Remove release agent with isopropanol and let the surface dry. For the Permabond cyanoacrylate process, apply POP primer, allow it to dry and bond promptly with the specified grade. Do not assume that this primer helps epoxy, acrylic or UV adhesives; it is product-system specific.
Silicone rubber
Remove release agent with isopropanol and let the surface dry. For the Permabond cyanoacrylate process, apply POP primer, allow it to dry and bond promptly with the specified grade. Do not assume that this primer helps epoxy, acrylic or UV adhesives; it is product-system specific.
How to do it
Dry-fit first. Meter, mix or prime exactly as the selected product requires. Apply a controlled bond line, assemble within working time, clamp without squeezing the joint dry and leave supported through the full stated cure.
Working, clamping and cure times
Follow the current Smooth-On Sil-Poxy instructions. Working time, handling strength and full cure are different. Cold conditions, thick beads and two impermeable faces can extend the cure.
If the conditions are harder
| Condition | Verdict | Notes |
|---|---|---|
| Outdoor use | Works with care | Smooth-On Sil-Poxy has manufacturer outdoor, weathering or UV-related evidence. That does not remove the need to seal porous edges, accommodate movement and keep the joint within product limitations. |
| Water and wet areas | Works with care | Smooth-On Sil-Poxy has manufacturer water-resistance or waterproof wording, but that wording is not expanded into continuous-immersion approval. Seal absorbent edges and keep the assembly within the exact documented exposure. |
| Heat and cold | Works with care | The product record states an upper service temperature of 260 degrees C and a lower service temperature of -45 degrees C. Use the narrower limit of the adhesive, both substrates, any coating and the joint design. |
Read the current safety data sheet. Provide ventilation, protect skin and eyes, and test an offcut for solvent attack, staining, stress cracking or coating lift. This is not an engineering approval for safety-critical loads.
Products that fit
Ordered by how well they suit this specific job. Nothing is ranked by what it pays.
Smooth-On Smooth-On Sil-Poxy
Silicone sealant
Official manufacturer documentation covers the relevant joint or both material classes without broadening its literal scope.
We may earn a commission from links on this page. It never changes which adhesive we recommend.
Related guides
Where this comes from
Reviewed 8 October 2026. Overall confidence: Strong evidence.
Sources used for this guide:
- 3M Bonding Solutions: Adhesives and Tapes Selection Guide (TECHNICAL_MANUAL)
- How to Bond Silicone (MANUFACTURER_PAGE)
- Permabond Adhesive Application Tips (MANUFACTURER_PAGE)
- Sil-Poxy Silicone Rubber Adhesive Technical Bulletin (TDS)
Always read the instructions and safety information supplied with the product you buy. Where they differ from anything here, follow the manufacturer.