What Is a 2 Part Polyurethane Rubber Kit?

A 2 part polyurethane rubber kit, or 2K polyurethane, is commonly used in the construction industry as a molding and casting material or precast concrete product. The material is packaged into two separate containers, which are meant to be combined just prior to use.

Most urethane rubber kits are categorized in terms of hardness. Since urethane rubbers are called elastomers, they use the same hardness scale, which is the Shore A Scale. A lower number on the scale means a softer, more flexible rubber. A higher number on the scale means a harder rubber that provides greater durability and long-term use. Soft rubbers are best for making molds with complex shapes or details, while hard rubbers are best for making tough, flat molds, formliners, or stamps.

2 part polyurethane rubber kits are excellent for casting concrete. They are mainly used to make molds for manufactured stone, cast stone, sculpture and décor reproduction, architectural restoration, and more.

Why Does Liquid Urethane Rubber Come as a Kit?

Urethane rubber comes as a 2-part kit because it requires precise mixing of each part so it can undergo a controlled chemical reaction to cure. The kit includes an A side and a B side; the A side is an isocyanate blend, and the B side is a poly/amine blend. Mix ratios of the A and B side materials can vary, with 1:1 or 2:1 by volume being the most common.

The chemical reaction can only occur once the A side and B side components are combined and mixed. When mixed, the two components chemically link, creating an irreversible exothermic reaction. The material will cure at room temperature to a flexible rubber with formulated properties. Being a liquid material at the start allows you to mold it into any shape you require.

Advantages of using a pourable urethane rubber kit include:

  • Ease of use: 2 part urethane rubber kits are easy to use, as many users like to measure their material by volume, so no scales are required.
  • Controlled pot life: By keeping the components separate until use, you can prepare everything else for molding before you pour the rubber.
  • Controlled cure time: Since the components are separate, they won’t start curing until they are mixed. You can ensure that your material will cure at the desired rate for your application.
  • Custom formulations: Varying the ingredients and the mix ratios of the two components creates different formulas. This allows for versatility in properties to meet requirements for various applications. Flexibility in formulation is much easier to achieve with two component kits.

How Do You Mix the A Side and B Side?

Before mixing, ensure your material, mold boxes or forms, and working area are at a proper working temperature. At VFI, we typically recommend temperatures above 65°F for the material to cure properly. Always check the technical data sheet provided by the manufacturer for specific instructions.

Not all urethane rubber products have the same mix ratios or handling procedures. Check the mix ratio before you start, as they can be listed by volume or weight on the technical data sheet. Following the mix ratio is crucial for your material to achieve the full formulated properties once cured.

Before mixing, prepare the equipment you’ll need. Spray release on your mold box or form for ease when demolding. We recommend having two clean, dry mixing containers, such as plastic buckets, and a hand mixer or mixing sticks. Depending on how you plan to measure your material, you may also want a scale. Also, wear proper PPE, including gloves and safety glasses, to avoid contact with the material. Once you are set up in a well-ventilated area, proceed with the following:

  • First, mix the B side. Some B side material may have settled in transit or storage, so we require mixing before pouring it into a clean container.
  • Weigh or measure the B side into a clean mixing container.
  • Weigh or measure the A side and pour it into the same mixing container. Once the A side material has been added to the B side material, your work time/pot life has begun.
  • Mix the A and B sides together using a hand mixer or mixing stick. Make sure to scrape the sides and bottom of the container while mixing to ensure a homogenous mix. Mix slowly to prevent air bubbles from forming in the material.
  • Pour the mixture into a new, clean container for a second mix. The double mix method will ensure that no unmixed material is used. Continue to scrape the sides and bottom while mixing.
  • After thorough mixing, the rubber should be immediately poured into a mold or form to cure.

If you do not use all your material, a nitrogen purge can help extend the shelf life of both the A and B sides. Do not save any material that has already been mixed. Only unmixed A and B sides can be purged.

How is 2-Part Urethane Different?

A 2 part polyurethane rubber kit allows for versatility and customization that other single and two component materials can’t provide. Chemistry can be adjusted to provide different properties, making them suitable for applications in various industries.

Urethane’s properties contribute to an increased lifespan of molds and forms made with the material. It has better abrasion resistance with excellent strength, durability, and dimensional stability. These properties are why urethane rubber is one of the most commonly used materials to cast concrete.

Its elastomeric properties allow it to be bent or compressed and still return to its original size and shape. This flexibility is vital for abrasive molding conditions since it results in less damage to the mold and casting. VFI has even developed a Max Release Molding Rubber series for easier demolding and reduced breakage rates. This is similar to the characteristics of silicone, but much better for concrete casting.

Also different from other materials is urethane’s ability to provide consistent performance under repeated casting. Many materials are only good for a few uses, while a single urethane mold is capable of producing up to one hundred castings. They are also typically less expensive than other similar rubber kits like silicone.

How Do I Find a Liquid Polyurethane Supplier?

The first step in finding a liquid polyurethane supplier is to conduct an online search. Search engines like Google can offer a vast amount of information when searching key terms like “liquid polyurethane rubber suppliers.”

Attending trade shows, exhibitions, and conferences is also a great way to connect with polyurethane manufacturers and suppliers. Look for events related to industries where the material is typically used. These events will generally have polyurethane companies showcasing their products so you can connect with them or other professionals who use the material.

Alternatively, you could also reach out to professionals in your industry who may use polyurethane. They may be able to guide you in the right direction or recommend reliable suppliers based on their experience.

VFI is a manufacturer of urethane rubbers, plastics, and coatings. Contact us today if you’re interested in hearing more about our products.