Smooth-Cast 327 ColorMatch 1 Gallon (6.81kg) Kit
Smooth-Cast 327 is a fast-cast liquid urethane resin from the Smooth-On ColorMatch 325 Series, formulated “colour neutral” so that pigments and fillers reproduce accurately in the cured casting. The gallon kit is the larger pack size, suited to repeat production runs, batch casting and bigger moulds where a small kit would run out mid-pour.
327 has the longest working window of the three ColorMatch resins: 10-20 minutes of pot life against 2.5 minutes for 325 and 7-9 minutes for 326. At volume that matters, because it is the difference between pouring one cavity and pouring a full mould board from a single mixed batch.
Typical applications
- Runs of pigmented prototype models and figures
- Special effect props
- Reproductions of small to medium size sculptures
- Batch-cast decorative jewellery
- Cold-cast metal effects using bronze, brass or other metal powders (Smooth-On publish a separate technical bulletin on metal cold casting)
Technical data
| Mix ratio | 1A:1B by volume, or 115A:100B by weight |
|---|---|
| Colour | Clear amber |
| Mixed viscosity | 100 cps (ASTM D-2393) |
| Specific gravity | 1.07 g/cc (ASTM D-1475) |
| Specific volume | 25.9 cu. in./lb (ASTM D-1475) |
| Pot life at 23°C | 10-20 minutes (ASTM D-2471) |
| Cure time at 23°C | 2-4 hours, depending on mass |
| Shore D hardness | 72 (ASTM D-2240) |
| Tensile strength | 3 170 psi (ASTM D-638) |
| Tensile modulus | 140 000 psi (ASTM D-638) |
| Elongation at break | 10% (ASTM D-638) |
| Flexural strength | 3 100 psi (ASTM D-790) |
| Flexural modulus | 95 700 psi (ASTM D-790) |
| Compressive strength | 3 080 psi (ASTM D-695) |
| Compressive modulus | 32 200 psi (ASTM D-695) |
| Shrinkage | 0.0075 in./in. (ASTM D-2566) |
| Heat deflection temperature | 50°C / 120°F (ASTM D-648) |
All values measured after 7 days at 23°C / 73°F.
Casting at volume: what to watch
Large mass castings get very hot and shrink more, depending on mould configuration, so plan wall thickness and pour mass around that rather than simply scaling up a small test part. Castings are extremely hot immediately after cure and may burn skin, so let them cool to room temperature before handling. Keep pigment and filler additions consistent by weighing them each time, and mix Part A and Part B thoroughly, scraping the sides and bottom of the container several times so that no unmixed material reaches the mould.
Colouring and filling
Pre-mix pigment or filler into Part B and blend to a uniform consistency before adding Part A. Around 0.5% to 1% Smooth-On pigment by weight of Part B yields rich, vivid colour, while 0.1% gives a translucent effect. The series works with So-Strong tints and Ignite colour pigments, and readily accepts fillers such as URE-FIL 3.
How to use it
- Store and use the material in a warm environment at roughly 23°C. Liquid urethanes are moisture sensitive and will absorb atmospheric moisture, so keep tools and containers clean and made of metal, glass or plastic.
- Apply a release agent to any surface that will contact the plastic. Brush a liberal coat over all surfaces with a soft brush, follow with a light mist coat, and let it dry for 30 minutes. Smooth-On silicone rubber moulds usually do not need a release agent unless you are casting silicone into them, although release will prolong mould life.
- Stir or shake Part A and Part B thoroughly before dispensing.
- Dispense equal volumes of A and B, or 115A:100B by weight, and mix thoroughly.
- Pour in a single spot at the lowest point of the containment field and let the mixture seek its own level to minimise air entrapment.
- Allow 2-4 hours to cure at room temperature, depending on mass and mould configuration.
- Post cure at 65°C / 150°F for 4 to 6 hours to reach full cure faster and achieve maximum physical properties, then let castings return to room temperature before handling.
Cured performance
Cured castings are rigid and durable. They resist moisture, moderate heat, solvents and dilute acids, and can be machined, primed, painted or bonded to other surfaces once any release agent is removed. Castings may be displayed outdoors after priming and painting. Unpainted castings will yellow over time, more quickly under ultraviolet light. ColorMatch castings stay semi-rigid for longer than other Smooth-Cast resins, depending on mass.
Storage and shelf life
Shelf life is reduced once containers are opened, which matters more on a gallon kit than a small one. Replace both lids immediately after dispensing and use remaining product as soon as possible. XTEND-IT Dry Gas Blanket significantly prolongs the shelf life of unused liquid urethane. Store in a cool, dry, well ventilated place away from heat, direct sunlight and strong oxidisers, keep containers tightly sealed, and avoid water contamination. Empty containers retain residue and should be handled accordingly.
Safety
Part A contains methylene diphenyl diisocyanate (MDI). Vapours may cause lung damage and sensitisation, and can be significant if the product is heated or sprayed. Part B is irritating to the eyes and skin. Use only with adequate room-size ventilation and do not breathe the fumes given off as the product gels and cures. Wear safety glasses with side shields, long sleeves and liquid-tight gloves such as butyl rubber, neoprene or PVC. Flush eyes with water for 15 minutes and get immediate medical attention in case of contact. Wear a dust mask when machining cured castings. Keep out of reach of children. Read the Safety Data Sheets for Part A and Part B before use.
Frequently asked questions
What is the mix ratio for Smooth-Cast 327?
1A:1B by volume, or 115A:100B by weight.
How long is the pot life and demould time?
10-20 minutes of pot life at 23°C, with a 2-4 hour cure depending on mass and mould configuration.
Is the gallon kit the same resin as the trial kit?
Yes. Same formulation and same published properties, supplied in a larger pack.
Can I cast large parts with it?
Yes, with care. Large mass castings get very hot and shrink more depending on mould configuration, so allow for that in your part and mould design.
How do I get the best physical properties?
Post cure the casting at 65°C for 4 to 6 hours after the room temperature cure.
Will the castings stay clear?
Unpainted castings yellow over time, more quickly with ultraviolet exposure. Priming and painting is recommended for pieces displayed outdoors.
Kit contents
Part A and Part B supplied in a 1:1 volume ratio. Because no two applications are quite the same, a small test application to determine suitability is recommended if the performance of this material is in question.
