Artists will need polyester and polyurethane resins when it is time for clay modeling and other forms of casting. This resin is the best for that kind of work since they sure and form a hard cast. They can also come off as glass, and shine through when they have been sanded and buffed. But you need to deduce which one to use. To make a better choice, you need to know how different these resins are.
Polyester resins are the cheaper alternatives in the market. There must be a catalyst or accelerator for it to work as needed. When you are casting, it shall give off a toxic odor, which means you need to have been prepared with a protective gas mask. The studio must be properly ventilated too. It then needs reinforcement in the form of a filler, such as fiberglass. After a while, they tend to develop spider web-like cracks.
There is also the fact that polyester resins cure to a clear finish. They shall however yellow out as time goes, when they come into contact with UV light. They will also be malleable for a short timeframe, necessitating the artist to work fast. They will be unusable after about ten minutes. They also have a high and unpredictable shrinkage rate, which adds to the difficulty of handling them. IT is used to bond fiberglass fabrics into hard sheets.
The polyurethane resins are more expensive of the two. They however have more uses to them. They have found work in rubbers, plastics, inks, medicines, and more. They are also hard enough to resist the beating from chemicals, oils, grease, and abrasion. When casting, they will not emit any harmful toxic gases.
They are normally presented as opaque and water clear resins. The casts formulated will display plenty of detail, and will not tear easily. You can use it to make plenty of plastic options, from the hardest to the smoothest. They are susceptible to forming bubbles, which necessitates treatment in a pressure pot or vacuum chamber. You also need to have special colors to paint on them. This makes its choice of colors more limited than other options.
The only issue with polyurethane resin is the moisture sensitivity it has. It needs a dry climate for proper curing. If you work in a humid place, you need to invest in a dehumidifier. They also cure fast, which is ideal. You only have to work fast when mixing and pouring it to get good results.
From this analysis, it is clear that polyurethane resins are the better choice for general mold making and casting works. They are the number one material in a clay studio. Polyester works well for fiberglass fabrications.