KX Flex™ 90

Description

This high-hardness urethane mold rubber is designed for applications requiring rigidity, abrasion resistance, and dimensional stability. 

With a Shore A90 hardness, KX Flex™ 90 acts like a semi-rigid elastomer, suitable for molds that need to maintain precise geometry under heavy loads or repeated casting cycles.

Features

• 1A:1B mix ratio by volume for accurate measurement and consistent curing.
• Typical working time of 20–25 minutes, allowing thorough mixing, optional degassing, and controlled pouring.
• Cures in about 16 hours at room temperature, achieving full mechanical performance with high tear strength and surface wear resistance.

Its firmness is ideal for concrete, plaster, gypsum, and filled resin systems where softer rubbers may deform or wear prematurely. 

The high Shore hardness helps maintain sharp edges, flat surfaces, and dimensional accuracy over long production runs, making it suitable for architectural elements, stone veneer molds, industrial tooling, and repetitive casting environments.

Despite its rigidity, it offers enough elasticity for demolding with proper draft and mold design. 

KX Flex™ 90 reproduces surface detail cleanly and resists cracking, compression set, and abrasion over time. 

KX Flex™ 90 can be poured as a block mold, used in jacketed systems, or combined with appropriate mold releases and pigments. 

Overall, it is an excellent option for professional mold makers requiring maximum durability and structural integrity from a Smooth-On urethane rubber.

Instructions

Preparation

• Store and use materials in a warm environment at 23°C.
• Use materials promptly as they have a limited shelf life.
• All liquid urethanes are moisture sensitive; use in low humidity (below 50% RH).
• Use clean mixing containers with straight sides and a flat bottom.
• Mixing sticks should be flat and stiff with defined edges.
• Mix in a well-ventilated area while wearing safety glasses, long sleeves, and rubber gloves.
• Conduct a small test application to ensure material suitability.

• Conduct a trial casting on a similar surface to avoid damage.
• Ensure polyurethane, latex, or metal molds are dry and apply a suitable release agent.
• Use Universal Mold Release for best results.
• Apply a liberal coat of release agent and brush lightly with a soft brush.
• Follow with a light mist coating and let dry for 30 minutes.

• Pre-mix Part B before each use.
• Mixing ratio: 100 Parts A to 120 Parts B by weight using a digital gram scale.
• Dispense Part A into a mixing container, weigh and add Part B.
• Hand mix thoroughly for at least 60 seconds, scraping sides and bottom.
• For mechanical mixing, use a turbine mixer for 30 seconds, then hand mix for 30 seconds.
• Material pot life is 2.5 minutes at 23°C; it decreases at higher temperatures.

• Pour mixture in a single spot at the lowest point of the mold.
• Avoid pouring directly over objects when encapsulating.
• Handling time can be as soon as 20 minutes; low mass castings may take longer.
• Uniform mild heat accelerates curing; full properties are reached in 7 days at room temperature.
• Post curing in a shop oven at 65°C for 4 hours is recommended for thin or low mass castings.
• Allow castings to cool to room temperature before handling.
• Ensure casting has reached handling strength before demolding.
• Allow material to cure for 24 hours at room temperature before use.
• Conduct a small test application to ensure material suitability.

Specifications