Polyester casting resin & polyester gelcoat

Properties of polyester resin

Polyester resin is easier to process than epoxy resin, which - unlike polyester resin - requires very precise attention to the proportions. However, it should be noted that polyester resin has a significantly higher shrinkage of 7 – 10 % than epoxy casting resin. A strong odour develops during processing.

Compared to epoxy casting resin, polyester resin is significantly cheaper.

Deaerate polyester resin before processing

Air bubbles can form when mixing the polyester resin components. If these air pockets remain in the casting compound, this can lead to unsightly casting results. To minimise the formation of air bubbles, it is important to proceed carefully when mixing the compounds. If you are using a stirring attachment for the drill, for example, run the device at the lowest possible stirring speed to prevent bubbles from forming.

In order to obtain an optimal casting compound, it is recommended to deaerate the casting resin in a vacuum after mixing the components. This is particularly recommended for very viscous compounds (high viscosity), as the air bubbles can hardly rise on their own. If you do not have the option of working with a vacuum pump, you can reduce the air bubbles in your casting compound by letting it run slowly over a wooden stirring spatula when pouring it into the mould, for example. You can also remove larger, visible air bubbles with a needle.

Do not cast larger blocks in one piece

If you want to produce larger blocks of polyester resin, we recommend casting them in layers of approx. 2 cm thickness each. If you process too large quantities of polyester resin at once, this will lead to a significant increase in temperature during the exothermic reaction for curing. This can damage the material, resulting in yellowing or even cracks. Each layer must first start to harden. As soon as the reaction temperature has decreased again, the next layer of casting resin can be applied.

Embedding objects in polyester resin

Please make sure that if you want to embed something in polyester resin, you only embed absolutely dry objects and objects, as moisture leads to the formation of unsightly streaks. If necessary, objects that are not completely dry can be treated in advance with a sealing release agent.

To prevent your object from sinking into the casting resin, first pour a layer of polyester resin into your mould and allow it to harden. You can then place the object on this base and add further layers of casting resin until the object is completely enclosed. Be careful not to place your object too close to the edge due to the strong shrinkage of the casting resin.

Colouring transparent polyester resin

With colouring pastes for synthetic resins and metal powders can be used to colour polyester resin very well.

Take care of your health!

To prevent damage to health, only work in well-ventilated rooms and wear protective clothing such as nitrile gloves , closed safety goggles and a suitable respirator mask.