RTV-1 vs. RTV-2 silicones: The complete comparison

When selecting the right silicone for technical applications, one is often faced with the fundamental question: RTV-1 or RTV-2? The designation RTV stands for "Room Temperature Vulcanization" and describes silicones that cure at room temperature. However, there are significant differences between one-component and two-component systems in terms of processing, properties, and areas of application.

What are RTV silicones?

RTV silicones are polydimethylsiloxane (PDMS)-based elastomers that crosslink at room temperature (15 to 30°C). Unlike high-temperature vulcanizing silicones (HTV), which require temperatures of 120 to 200°C, crosslinking in RTV systems occurs through chemical reactions at ambient conditions.

RTV-1 (One-component): Ready-to-use silicones that cure by reacting with atmospheric moisture. They cure from the outside in. Typical curing rate: 2-3 mm per 24 hours.

RTV-2 (two-component): Consists of a base and a hardener (catalyst) that must be mixed before processing. Crosslinking occurs uniformly throughout the entire volume, regardless of the layer thickness.

Networking mechanisms

Condensation crosslinking

In condensation crosslinking, silicon chains are linked together with the release of small molecules (acetic acid, alcohol, oxime, or amine). This mechanism is used in all RTV-1 and some RTV-2 systems.

• Acetate system: Releases acetic acid (typical odor). Fast curing, good adhesion to glass and ceramics.
• Alkoxy system: Releases methanol. Neutral crosslinking, corrosion-free, ideal for sensitive substrates.
• Oxime system: Releases butanone oxime. Good depth curing, suitable for thicker layers.

Addition crosslinking (platinum-catalyzed)

In addition crosslinking, vinyl and hydride groups are linked under platinum catalysis without the release of byproducts. This mechanism is used exclusively in RTV-2 systems.

• No shrinkage (no waste products)
• Precisely controllable pot life and curing times
• Food-safe and skin-friendly options available
• Sensitive to catalyst poisons (sulfur, amines, tin)

Comparison table: RTV-1 vs. RTV-2

When to vote for RTV-1

• Seals and joints: Thin beads and layers up to max. 10 mm
• Bonding: Glass to metal, plastic to ceramic
• Electronic potting: Thin protective layers on circuit boards
• Repairs: Fast on-site applications without mixing equipment
• Prototyping: Fast, uncomplicated sealing.

When to vote for RTV-2

• Mold making: Flexible silicone molds for casting in resin, plaster, concrete
• Technical components: Precision seals, membranes, buffers
• Encapsulating compounds: Complete embedding of electronics and sensors
• Food contact: baking molds, dispensing valves, seals
• Medical technology: Skin-compatible components, prosthetic elements
• Large volumes: Parts with any layer thickness

Processing tips

Properly process RTV-1

• Substrates must be clean, dry, and free of grease
• For thick layers (>6 mm): Apply in several layers
• Optimal conditions: 23°C, 50% relative humidity
• Use primers for difficult substrates (PE, PP, PTFE)

Properly processing RTV-2

• Adhere to the exact mixing ratio (use a precision scale)
• Mix thoroughly (2-3 minutes), also scraping off the sides and bottom of the container
• Evacuate after mixing (vacuum chamber, 20-50 mbar)
• Apply release agent to the model (Vaseline or special silicone release agents)
• Pour slowly and without bubbles

FAQ

Conclusion

RTV-1 and RTV-2 silicones each have distinct strengths. RTV-1 is the first choice for fast, straightforward sealing and bonding in thin layers. RTV-2 is superior for mold making, technical components, and anywhere precision, mechanical strength, and through-curing are required regardless of layer thickness.