Silicone Sealants — Complete Guide
Silicone sealants are flexible, waterproof, durable materials used to seal joints & gaps, bond glass, and weatherproof building elements. Cured from a paste to a rubbery elastomer, silicone offers excellent flexibility, UV / weather resistance, water resistance, and adhesion to glass, metal, ceramic and most non-porous surfaces. From sealing bathroom joints and glazing windows to structural glazing of glass facades, silicone is indispensable in modern construction.
Silicone sealants follow ASTM C920 / EN 15651. Major brands: Dow (Dowsil), GE Momentive, Wacker, Sika, McCoy, Pidilite (Fevicol), Soudal, Bostik, Anabond.
Types of Silicone Sealant (by Cure)
| Type | Cure / Property | Use |
|---|
| Acetoxy Cure | Releases acetic acid (vinegar smell); fast cure, strong | Glass, ceramic, glazing (non-porous, non-metal) |
| Neutral / Oxime Cure | Odourless, non-corrosive; bonds metal & masonry | Metal, stone, mirrors, weatherproofing |
| Alkoxy Cure | Neutral, low odour | Sensitive substrates, electronics |
Acetoxy vs Neutral: Acetoxy is cheaper & faster but its acetic acid corrodes metals & stains marble / concrete — use only on glass / ceramic. Neutral cure is non-corrosive & bonds metals, stone & mirrors — use for structural / weatherproofing & sensitive substrates.
Types by Application
| Type | Use |
|---|
| General Purpose Silicone | Gaps, joints, sealing |
| Sanitary / Bathroom Silicone | Anti-fungal, wet areas (basins, tubs, joints) |
| Weatherproofing Silicone | Exterior joints, expansion joints |
| Structural Glazing Silicone | Bonds glass to facade frame (load-bearing) |
| Mirror Silicone | Mirror-safe (no backing damage) |
| Fire-Rated Silicone | Fire-stopping joints |
| High-Temperature Silicone | Up to 300 °C (RTV) |
| Aquarium Silicone | Non-toxic, water-safe |
Properties
| Property | Value |
|---|
| Elongation | up to 25–50% (movement capability) |
| Service Temp | −50 to +150 °C (up to 300 °C HT) |
| UV / Weather Resistance | Excellent |
| Water Resistance | Excellent (waterproof) |
| Adhesion | Excellent (glass, metal, ceramic) |
| Cure Time | Skin 5–20 min; full 24–72 hr |
| Tack-Free | 10–30 min |
| Lifespan | 10–20+ years |
| Paintable | No (silicone); use acrylic / PU if painting needed |
Where to Use
- Bathroom & kitchen joints (sanitary silicone)
- Sealing around basins, sinks, tubs, WC
- Window & door glazing (glass to frame)
- Structural glazing (glass facades)
- Weatherproofing exterior joints
- Expansion / movement joints
- Mirror fixing (mirror silicone)
- Aluminium / UPVC window sealing
- Fire-stopping joints (fire-rated)
- Gap sealing (waterproof)
- Aquariums (aquarium grade)
- HVAC / ducting (high-temp)
Silicone vs Other Sealants
| Parameter | Silicone | PU Sealant | Acrylic Sealant |
|---|
| Flexibility | Excellent | Excellent | Moderate |
| UV Resistance | Excellent | Good | Moderate |
| Adhesion to Glass/Metal | Excellent | Good | Poor |
| Paintable | No | Yes | Yes |
| Movement Joints | Excellent | Excellent | Limited |
| Cost | Medium-High | High | Low |
| Best For | Glazing, wet, weatherproof | Flooring, paintable joints | Internal cracks, paintable |
See PU & PVA adhesives for paintable / bonding alternatives.
Top Brands
| Brand | Products |
|---|
| Dow (Dowsil) | Structural glazing, weatherproof silicones (premium) |
| GE Momentive | Silicone sealants |
| Wacker | Elastosil silicones |
| Sika | Sikasil structural & weatherproof |
| McCoy | Silicone sealants (popular) |
| Pidilite (Fevicol) | Silicone sealants |
| Soudal / Bostik / Anabond | Sealants range |
Application Process
- Clean joint / surface (remove dust, oil, old sealant)
- Mask edges with tape for neat lines
- Insert backer rod for deep joints (correct depth)
- Load cartridge in caulking gun; cut nozzle to bead size
- Apply continuous bead into joint
- Tool / smooth with finger / spatula (soap water)
- Remove masking tape before skin forms
- Allow to cure (24–72 hr)
- For structural glazing, follow design joint dimensions strictly
Advantages
- Excellent flexibility (movement joints)
- Outstanding UV / weather resistance
- 100% waterproof
- Excellent adhesion to glass / metal / ceramic
- Wide temperature range
- Long lifespan (10–20+ years)
- Anti-fungal (sanitary grade)
- Structural glazing capability
- Neutral cure = non-corrosive
- Available in colours & clear
- Doesn't shrink / crack
Disadvantages
- Not paintable (silicone)
- Acetoxy corrodes metal / stains marble
- Higher cost than acrylic
- Hard to remove / re-do
- Poor adhesion to porous surfaces (without primer)
- Attracts dust (uncured / low quality)
- Cannot bond to itself once cured
- Skilled application for structural glazing
- Mould growth on cheap non-sanitary in wet areas
Common Problems
- Mould / fungus (non-sanitary in wet areas)
- Poor adhesion (dirty / porous / wet surface)
- Acetoxy corrosion on metal / marble stains
- Bubbling (applied in rain / damp)
- Cracking (over-thin bead / wrong joint design)
- Dust pickup (low quality)
- Discolouration (cheap clear silicone)
- Structural glazing failure (wrong product / joint size)
Cost (Approximate, Indian Market, 2025-26)
| Item | Cost (per cartridge ~280–300 ml) |
|---|
| General Purpose Acetoxy | Rs 120 – 250 |
| Sanitary / Bathroom Silicone | Rs 180 – 350 |
| Neutral Cure Weatherproof | Rs 250 – 500 |
| Structural Glazing Silicone | Rs 400 – 900 |
| High-Temperature (RTV) | Rs 250 – 600 |
| Premium (Dow / Wacker) | Rs 400 – 1,200 |
| Caulking Gun | Rs 150 – 800 |
Best Practices
- Use neutral cure for metal / stone / mirrors (non-corrosive)
- Use acetoxy only on glass / ceramic
- Use sanitary (anti-fungal) silicone in bathrooms / kitchens
- Use structural glazing silicone (Dow / Sika) for glass facades — designed joint sizes
- Clean & dry surface; use primer on porous substrates
- Use backer rod for deep joints (correct depth-to-width ratio)
- Mask edges for neat beads
- Don't apply in rain / on wet surface
- Tool the bead for adhesion & finish
- Don't paint over silicone (use PU / acrylic if paint needed)
- Allow full cure before water / load exposure
- For structural glazing, use qualified applicators & product certification
- Check shelf life (expired silicone won't cure)
Applicable Standards
| Standard | Description |
|---|
| ASTM C920 | Elastomeric Joint Sealants |
| EN 15651 | Sealants for Non-Structural Joints |
| ASTM C1184 | Structural Silicone Sealants |
| EN 13022 | Structural Sealant Glazing |
| ASTM C794 | Adhesion-in-Peel of Sealants |
| ISO 11600 | Building Construction Sealants Classification |
Conclusion
Silicone sealants are the go-to for flexible, waterproof, weather-resistant sealing — from bathroom joints to glass facade structural glazing. Choose neutral-cure for metal / stone / mirrors (non-corrosive), acetoxy only for glass / ceramic, and sanitary anti-fungal grade for wet areas. For glass facades, use certified structural glazing silicone with designed joint dimensions. Silicone is not paintable — use PU / acrylic where paint is needed.
For paintable / bonding needs, see PU & PVA adhesives; for tile joints, tile adhesive & epoxy grout; silicone seals UPVC / aluminium windows & glass assemblies.