Smooth-On Epoxacast 690

Availability: In stock (4)

EpoxAcast™ 690 is a clear casting epoxy resin suitable for a variety of industrial and art-related projects requiring a rigid, clear finished casting. It is mixed 100A:30B by weight (gram scale required) and features a very low viscosity for easy mixing and minimal bubble entrapment. Working time is 5 hours and cure time is 24 hours at room temperature. Castings cure with negligible shrinkage and are very hard and strong. Resin can be colored with UVO™ or IGNITE™ colorants. This product is not moisture sensitive and can be used in humid environments. Recommended casting thickness maximum per layer is 3/8 in. / 0.95 cm.


  • Optically clear
  • Perfect for lenses or encapsulation


Preparation – Avoid breathing fumes - use in a well ventilated area at minimum. NIOSH approved respirator is recommended. Wear safety glasses, long sleeves and rubber gloves to minimize skin contact.

Materials should be stored and used in a room temperature environment (73°F/23°C). Elevated temperatures will reduce Pot Life. EpoxAcast™ 690 Resin and Hardener must be properly measured and thoroughly mixed to achieve full, highstrength, solid-cure properties.

Because no two applications are quite the same, a small test application to determine suitability for your project is recommended if performance of this material is in question.

Applying A Release Agent – For releasing epoxy from non-porous surfaces such as resin, metal, glass etc., use Ease Release™ 200 or 205 (available from Smooth-On) to prevent adhesion.

IMPORTANT: To ensure thorough coverage, lightly brush the release agent with a soft brush over all surfaces of the mold or model. Follow with a light mist coating and let the release agent dry for 30 minutes.

Measuring / Dispensing – The proper mixing ratio is 100 parts of EpoxAcast™ 690 resin to 30 parts hardener by weight. You must use an accurate scale (gram scale or triple beam balance scale) to weigh these components properly. Do not attempt to measure components by volume.

Mixing tools and containers should be clean and dry. Mixing should be done in a well ventilated area. Wear safety glasses, long sleeves and rubber gloves to minimize contamination risk. Combine EpoxAcast™ 690 resin with the appropriate amount of hardener. Mix thoroughly for 3 minutes making sure that you scrape the bottom and sides of the container several times.

Adding Color - EpoxAcast™ 690 can be colored with UVO™ or IGNITE™ colorants or Cast Magic™ Effects Fillers. Pre-mix color or filler with Part A thoroughly and then add Part B.

Mixing – Be sure mixing utensils are clean and free of any potential contaminants such as dirt, dust or grease. Mix Parts A and B thoroughly for at least 3 minutes with a square edged mixing stick. Be aggressive and scrape sides and bottom of mixing container several times. Use the square edge of mixing stick to bring material off of the sides of container and blend. If using a drill mixer, follow with hand mixing as directed above to ensure thorough mixing.

Adding Fillers - A variety of dry fillers can be added. Pre-mix dry filler with Part A before adding Part B.

Increasing Flexibility - Flexer™ Epoxy Flexibilizer is a clear, low viscosity liquid additive that will lower the durometer (Shore hardness) of some SmoothOn casting and laminating epoxies. When added to the epoxy system in the proper proportion, the cured epoxy will be softer and, in some cases, can be made semi-rigid. See the Flexer™ Technical Bulletin for more information.

IMPORTANT: Mixed EpoxAcast™ 690 is exothermic, meaning it generates heat. A concentrated mass of mixed epoxy in a confined area such as a mixing container can generate enough heat to melt a plastic cup, burn skin or ignite combustible materials if left to stand for its full Pot Life. Do not use foam or glass mixing containers or pour sections thicker than 3/8 in. / 0.95 cm. If a batch of mixed epoxy begins to exotherm, move it to an open air environment.

Pouring – If casting EpoxAcast™ 690 into a rubber mold, pour mixture in a single spot at the lowest point of the mold or enclosure. Let the mixture seek its level. A uniform flow will help minimize entrapped air. Recommended casting thickness maximum 3/8 in. / 0.95 cm.

Layer Pouring - When pouring EpoxAcast™ 690 in layers, allow previous layer to fully cure and come to room temperature (73°F / 23°C) before pouring additional layers.

Cure Time: Refer to specified Cure Times at room temperature depending on mass. Cured material will be hard and unable to penetrate with a finger nail. Cured epoxy can now be dry sanded. If machining or sanding, wear NIOSH approved mask to prevent inhalation of particles. Pot Life and Cure Time values are dependent on mass and mold configuration, as epoxies are mass-sensitive. Let cure for 24 hours at room temperature. Castings that are ¼ in. thickness or less will cure more slowly and may require up to 48 hours to fully cure at room temperature.

Performance: Cured castings are very hard 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 castings, wear dust mask or other apparatus to prevent inhalation of residual particles.

Castings can be displayed outdoors after painting with an aliphatic urethane clear coat. Unpainted castings will yellow after being exposed to UV light or excessive heat above 115°F/46°C. For longer outdoor UV resistance of an unpainted clear part, Smooth-On’s Crystal Clear™ Urethane Resin may be an option for your application.

Because no two applications are the same, a small test application to determine suitability is recommended if performance of this material is in question.

Painting – Cured EpoxAcast™ 690 can be painted and / or primed and then painted with acrylic enamel paints. Let paint fully dry before putting part into service.

Removing EpoxyUncured / Non-curing epoxy: Scrape as much material as possible from the surface using a scraper. Clean the residue with E-POX-EE KLEENER™ available from Smooth-On, lacquer thinner, acetone or alcohol. Follow safety warnings pertaining to solvents and provide adequate ventilation.


Mix Ratio by Weight: 100A : 30B
Mixed Viscosity - CPS. (ASTM D2393): 280
Specific Gravity - Mixed; g./c.c. (ASTM D1475): 1.10
Spec. Volume - Mixed; cu. in./lb. (ASTM D792) : 25
Pot Life - (ASTM D2471)T: 5 Hours
Cure Time - Standard Casting Method: 24 Hours
Cure Time - Fan Cooled Casting Method: 36 Hours
Color: Clear
Shore D Hardness (ASTM D2240): 80
Ultimate Tensile - P.S.I. (ASTM D638) : 6,630
Tensile Modulus - P.S.I. (ASTM D638): 572,000
Tensile Elongation (ASTM D638): 1.8
Flexural Strength - P.S.I. (ASTM D790): 10,980
Flexural Modulus - P.S.I. (ASTM D790): 410,000
Compressive Strength - P.S.I. (ASTM D695): 9,610
Compressive Modulus - P.S.I. (ASTM D695): 91,300
Shrinkage - in./in. (ASTM D-2566): 0.002
Heat Deflection Temp. (ASTM D648) If cured at room 70°F / 21°C: 115°F/46°C
Index Of Refraction: 1.565 nm
Values for EpoxAcast™ 690 measured after 7 days at 70°F / 21°C:
*Pot Life and Cure Time values are dependent on mass and mold configuration, as epoxies are mass-sensitive.:
0 stars based on 0 reviews
Please accept cookies to help us improve this website Is this OK? Yes No More on cookies »