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Ultra-Low Viscosity Liquid Plastic


Smooth Cast 300 is a new ultra-low viscosity casting resin that yields virtually bubble free castings in 7 - 10 minutes (depending on mass and mold configuration). Easy to mix and pour, SC 300 offers the convenience of a one to one mix ratio (one part A to one part B by volume).

SC 300 readily accepts fillers (such as URE-FIL 3) and can be pigmented. (Smooth-Cast 320 accepts pigments better than SC 300). This product is superior for cold cast metal applications. Fully cured castings are tough, durable, machinable and paintable. They resist moisture and mild solvents. Applications for SC 300 include reproducing small to medium size sculptures, cold cast bronze, making prototype models, special effect props, decorative jewelry, etc.

Go "Foam Crazy" with SC 300! By adding additional components, SC 300 can be foamed to achieve a variety of different properties and effects.

Key Values:

Mixing Ratio: One to One by volume. Color: White Durometer: Shore 70D
Pot Life: 2 - 3 minutes   Demold Time: 7 - 10 minutes (depending on mass)


Mixed Part A + B White 100 cps 1.05 26.6
Shore D Hardness: 70 Ultimate Tensile Strength: 3,000 PSI Shrinkage: .01 in./in.

Description: SC 300 consists of two liquid components, Part A (Yellow Label) and Part B (Blue Label). When combined in a mixing ratio of one to one by volume, SC 300 quickly cures to a solid and durable plastic.


Preparation . . . All liquid urethanes are moisture sensitive and will absorb atmospheric moisture. Mixing tools and containers should be clean and made of metal, glass or plastic. Mixing should be done in a well ventilated area. Wearing eye protection, latex gloves and long sleeve garments to minimize skin contact is strongly recommended.

Applying A Release Agent . . . A release agent is necessary to facilitate demolding when casting into or over most surfaces. Use a release agent made specifically for mold making (Universal Mold Release or Mann’s Ease Release 2251). A liberal coat of release agent should be applied onto all surfaces that will contact the plastic. ~IMPORTANT: To ensure thorough coverage, lightly brush the release agent with a soft brush over all surfaces. Follow with a light mist coating and let the release agent dry for 30 minutes.

Most silicone rubber molds usually do not require a release agent unless casting silicone into the mold. Applying a release agent, however, will prolong the life of the mold.

Mixing . . . After dispensing equal amounts of Parts A and B into mixing container, mix thoroughly. Stir slowly and deliberately making sure that you scrape the sides and bottom of the mixing container several times. Be careful not to splash low viscosity material out of the container.

Remember, SC 300 sets up quickly. Do not delay between mixing and pouring.

IMPORTANT: Shelf life of product is drastically reduced after opening. Remaining product should be used as soon as possible. Immediately replacing the lids on both containers after dispensing product will help prolong the shelf life of the unused product. XTEND-IT Dry Gas Blanket will significantly prolong the shelf life (up to 4 times longer) of unused liquid urethane products.

Pouring . . .For best results, pour your mixture in a single spot at the lowest point of the containment field and let the mixture seek its level. This will help minimize air entrapment.

Curing . . .SC 300 will cure in 7 - 10 minutes depending on mass and mold configuration. Non-hazardous fumes, which may be visible as this product starts to "gel" and cure, will dissipate with adequate (room size) ventilation. Post curing (heating your casting to 150F/65C) for 4 – 6 hours increases physical properties and performance.

Performance . . .Cured castings of SC-300 are rigid and durable. They resist moisture, moderate heat, solvents, dilute acids and can be machined, primed/painted or bonded to other surfaces (any release agent must be removed). If machining cured SC300, wear dust mask or other apparatus to prevent inhalation of residual particles. Castings can be displayed outdoors after priming and painting. Unpainted castings will yellow over time - more quickly when exposed to ultra-violet light. Because no two applications are quite the same, a small test application to determine suitability is recommended if performance of this material is in question.

Go "Foam Crazy" With SC 300

By adding water, Urefil 3 Filler and SO-Cure Cure Accelerator in specific proportions, SC300 can be consistently foamed to achieve a variety of properties and effects. Different foam densities are possible (10 lb. – 23 lb.) .

The material safety data sheet (MSDS) for this or any Smooth-On product should be read before using and is available on request. All Smooth-On products are safe to use if directions are read and followed carefully.

Be careful. SC 300 Part A (Yellow Label) contains methylene diphenyldiisocyante. Vapors, which can be significant if prepolymer is heated or sprayed, may cause lung damage and sensitization. Use only with adequate ventilation. Contact with skin and eyes may cause severe irritation. Flush eyes with water for 15 minutes and get immediate medical attention. Remove from skin with soap and water. Part B (Blue Label) is irritating to the eyes and skin. Avoid prolonged or repeated skin contact. If contaminated, flush eyes with water for 15 minutes and get immediate medical attention. Remove from skin with soap and water. When mixing with Part A, follow precautions for handling isocyanates. If machining cured SC300, wear dust mask or other apparatus to prevent inhalation of residual particles.


Important - The information contained in this bulletin is considered accurate. However, no warranty is expressed or implied regarding the accuracy of the data, the results to be obtained from the use thereof, or that any such use will not infringe a copyright or patent. User shall determine suitability of the product for the intended application and assume all associated risks and liability.

Call Us Anytime With Questions About Your Application.

Toll-free: (800) 9-SCULPT Fax: (212) 243-6374