Material guide
Silicone & rubber
What works on silicone and rubber: which glues hold and which peel off, how to cut and punch clean holes, and why you can't paint silicone caulk.
Quick facts
- Why glue fails
- Cured silicone has a very low surface energy, about 24 mN/m by one industry figure. Most glues bead up and peel off.
- Best glue for silicone
- Silicone adhesive (Sil-Poxy) or 100% RTV silicone. Sil-Poxy: 5 min work time, full cure in 24 hours.
- Super glue
- Bonds many rubbers, such as seals and O-rings. Not silicone or foam rubber.
- Oily rubber
- Rubber high in oil or plasticizer can stop even Gorilla products from holding
- Paint
- 100% silicone won't take paint. Use a paintable caulk where you plan to paint.
- Holes
- Punch them with a hollow punch over wood, rather than drilling
Silicone and rubber both stretch, bend and spring back. That's what makes them great for seals, gaskets, phone cases and baking mats. It's also what makes them hard to glue and cut.
They aren't the same material, though. Natural rubber, neoprene and EPDM are carbon-based rubbers. Many glues hold on them. Silicone is built on silicon and oxygen instead. Its surface is so slick and non-stick that almost nothing bonds to it except more silicone.
That one fact explains most failures. Super glue, Gorilla Glue and epoxy sit on top of cured silicone and peel off in one piece. Paint beads up on it. The fix is to glue silicone with a silicone adhesive, and to use a paintable caulk anywhere you plan to paint.
Soft rubber also fights cutting tools. A drill bit grabs and tears it, and a dull blade drags. Sharp blades, light passes and hollow punches give clean edges.
Drill into silicone & rubber
Don't drill soft rubber or silicone if you can avoid it. A twist bit grabs and tears it. Lay the sheet on a scrap of wood and strike a sharp hollow punch with a hammer instead.
What to use: Hollow punch set
Guides
- How to drill rubber or silicone cleanly (coming)
Cut silicone & rubber
Thin sheet cuts with sharp scissors or a fresh utility blade along a straightedge. Score thick sheet with several light passes instead of one hard one. Change blades often, since a dull edge drags and tears the rubber.
What to use: Utility knife with fresh blades + steel rule
Guides
- Cut thick rubber or silicone sheet cleanly (coming)
Glue silicone & rubber
Glue silicone with silicone: Sil-Poxy or 100% RTV silicone on a clean, dry surface. Super glue, Gorilla Glue and epoxy peel off cured silicone. Other rubbers are easier. Super glue holds many seals and O-rings, but not foam rubber.
What to use: Sil-Poxy for silicone; super glue gel for most other rubber
Guides
- Does Gorilla Glue work on silicone?
- does super glue work on silicone (coming)
- What glue sticks to silicone rubber? (coming)
- Is Gorilla Glue silicone-based? (What it's actually made of) (coming)
- Does Gorilla Glue work on rubber? (coming)
- Glue for rubber to metal and rubber to rubber (coming)
- What super glue won't stick to (and what to use instead) (coming)
Screw or anchor into silicone & rubber
Rubber won't hold a screw by itself. Clamp it, or bolt through it with wide washers so the bolt head can't pull through. For a seal, run a bead of 100% silicone. New silicone bonds to clean, cured old silicone, but cut away anything loose first.
What to use: Bolts with wide washers; 100% silicone for seals
Guides
- Silicone vs acrylic latex caulk: which to use where (coming)
- Does anything stick to silicone caulk? (coming)
Sand or finish silicone & rubber
You can't sand or paint silicone into shape. Paint beads up on it. Cut old silicone caulk out with a scraper or remover tool, then clean the joint and let it dry. Wipe silicone parts with isopropyl alcohol before you glue them.
What to use: Caulk remover tool + isopropyl alcohol
Guides
- Caulk won't stick or keeps peeling: the usual causes (coming)
Safety basics
- Keep blades sharp and hands clear. Rubber grabs a blade, and a slip with a utility knife cuts deep. Cut away from your body.
- Wear gloves with super glue. It bonds skin in seconds. Use nitrile gloves.
- Air out the room. Fresh silicone caulk and solvent wipes give off vapors. Open a window while they cure.
- Protect your eyes. Punches and hammers can throw chips.
Sources
- Enhancing silicone adhesion: low surface energy of cured silicone (Fastenal Blueprint)
- Sil-Poxy silicone rubber adhesive: tin- or platinum-cure silicone, 5 min work time, 24 h cure, abrade and solvent-wipe (Smooth-On)
- LOCTITE Super Glue Gel technical data sheet: bonds rubber seals and O-rings; do not use on silicone or foam rubber; not for high-flex repairs (Henkel)
- LOCTITE Plastics Bonding System technical data sheet: not for silicone rubber (Henkel)
- Gorilla 100% Silicone Sealant: not paintable, light-duty adhesive, may not hold on rubber high in oil or plasticizer (Gorilla Glue Company)
- Original Gorilla Glue: product page and FAQ (Gorilla Glue Company)
- Everything you need to know about caulking when painting: 100% silicone does not take paint, strip old material first (GE Sealants)
- Hammer-driven gasket and washer punches: for rubber and gasket material (McMaster-Carr)