There are resins and then there is polyurethane resin. This can be used for making different kinds of plastic objects. Knowing the features and usage will help artists make a start with resin casting.

Many of the hard plastic objects we see around us are actually made of polyurethane resins. And that too by mold casting!

Indeed, polyurethanes are nothing but synthetic resins that cure to a hard and solid surface. These are used extensively for making casts apart from foam, adhesives, paints, coatings and more.

Features of polyurethanes

Polyurethane casting resins are basically a two-part system consisting of the resin base and a hardener. They are mixed in the specified quantities before use. The material tends to capture air – therefore, careful mixing and slow pouring is advisable. Degassing in a pressure pot will further ensure bubble-free castings.

These are fast-curing resins with a short pot life. The advantage here is that the quick curing allows the cast to be demolded fairly quickly.

It is possible to play around with the resin – like add an inhibitor to extend the pot life, colorants to transform the appearance and even fillers to change the weight, stiffness, hardness, etc. The commonly used ones are glass fibers, cotton flocks, nylon fiber, talc, calcium carbonate, etc. Cold casting powders can be mixed, brushed or sprayed on the resin to get the effect of metal, wood, stone, etc.

Working with polyurethanes

The naturally low viscosity of polyurethane resin makes it easy to blend and work with. It has a good flow and yields excellent filling properties. There may be slight shrinkage when curing, but the cured resin displays high heat resistance.

It can be cast in both rigid and flexible molds to make lightweight plastic objects or artworks. However, using an appropriate release agent is essential to ensure easy demolding without damaging the mold and cast. This should be applied sparingly to avoid surface distortions in the detailing of the mold. Allow it to dry for 10 minutes or so prior to use.

The best way to pour the resin is to slightly tilt the mold and pour into one spot of the mold.Go slow as this will break the bubbles that may otherwise surface later as tiny imperfections on the casting. The resin will usually cure within 10 to 15 minutes at the most.

Polyurethane resins are commonly used for making artistic and unique jewelry items by encapsulating dried flowers, stones, shells and other personal keepsakes. The water clear resin options are especially popular for a variety of applications such as point-of-purchase displays, rapid prototypes, special effects, sculpture reproductions, giftware, etc. The same resin is used in manufacturing for making different items by way of injection casting.

In sum, resin casting is an interesting activity for newbies and artists apart from its usage in industries. Here it is important to use quality materials in the proper manner to ensure that the castings turn out as desired!