Different types of resins are regularly used for making casts. Polyester, epoxy and polyurethanes may all be resins, but their properties vary greatly. Many people just end up getting confused about which resin is suitable for a particular purpose.
A detailed look at each class of resin can help clear the uncertainty:
Polyester resin – This is a viscous liquid that is well-resistant to heat, fire and chemicals. It is flexible, cheap and comes in a variety of colors. The excellent features of polyester resin are commonly used to make any porous material rigid and weather resistant – such as fiber glass, bottles, surfboards, skis, fishing rods, laminates and so on. It enjoys great use in fabricating various parts of ships, aircraft and so on.
While it is quite easy to use, there are numerous other issues associated with polyester resin. It needs to be reinforced with fiber glass to make it mechanically strong. It tends to shrink unpredictably, turns yellow with age, can break easily and lets off a noxious odor. In fact, the user has to use safety gloves, goggles and a respirator to protect himself from the carcinogenic fumes. Proper ventilation is required even during curing to safely air out the fumes.
Epoxy resin – This is the highest performing resin but works out the most expensive too. It has a brownish color and clear ones tend to cost even more. Epoxy resin boasts of excellent mechanical, chemical, electrical and weather resistant properties, making it a favorite in ship, boat and aircraft components. This resin has low shrinkage and strong adhesive properties. Additionally, there are no toxic odors either.
However, it may take several hours or even days to cure completely. This can still be hastened by changing the curing agent. It is used for multiple purposes – as an adhesive, sealant, paint, varnish and for casting purposes.
Polyurethane resin – This is a versatile, tough and durable material. It has good physical, chemical and electrical properties and can be effectively combined with other resins to increase its usefulness. Polyurethanes come in various viscosities, tend to cure quickly and have a low odor that does not require a respirator either. The only drawback is the moisture sensitivity – they fail to cure properly in humid conditions or in molds containing water.
Polyurethane resin is used as an adhesive, insulation, foam liner in clothing and quick casting of prototypes. Polyurethane casting resins come in opaque and water clear varieties. The former set within a few minutes itself to an ivory color while the latter take a little longer and also need to be de-aired prior to use. Polyurethane casting resins are suitable for making cold castings and expandable ones are also available in the market.
In sum, there are various casting resins and each comes with its own set of benefits and downsides. While polyester resin will cost low, it can be dangerous to use and polyurethane resin may be heavier on the pocket but trumps in versatility and tenacity.