HDPE & Silicone Mould Care and Instructions

Thank you for purchasing our casting moulds. The guidance below explains how to care for our HDPE, silicone and Less-Resin moulds and how to get the best use from them.

HDPE mould care and instructions

We recommend using a suitable mould release, even where a resin manufacturer states that it is not required. Mould release can make de-moulding easier and can also help protect the mould and silicone bungs or plugs from wear caused by some resins.

Our shallower HDPE moulds, up to 25mm deep, have a silicone vacuum-release bung in the centre of each cavity to help with de-moulding without dismantling the mould. Deeper moulds also have a silicone bung, although the greater surface area means they may still need to be dismantled for de-moulding. Cube and sphere moulds generally need their end panels unscrewed.

If dismantling a mould, it can help to mark the sections with a permanent marker before taking it apart so the parts can be returned to their original positions. Remove excess resin before reassembly and do not overtighten the screws, particularly when using a powered screwdriver. HDPE is relatively soft and the screw threads can be stripped.

We use 3.5mm flange-head screws on our moulds. If a thread becomes stripped, a slightly thicker 4mm screw and later a 4.5mm screw can provide further repair options.

Preheating: If preheating an HDPE mould before casting, we recommend a maximum temperature of 60°C (140°F).

De-moulding an HDPE mould

First remove the bung from each cavity. Give the bottom of the mould a few taps with a dead-blow hammer or soft mallet. You can then carefully use pressurised air through the bung hole or a small punch through the hole to help release the cast. Deeper moulds may also need a couple of taps on each side.

Before reinserting the bungs, apply mould release for lubrication and push them in without twisting until fully inserted. For extended storage, remove plugs and bungs so the silicone is not kept compressed.

Browse our HDPE Pen Blank & Resin Casting Moulds or read our HDPE Moulds for Resin Casting guide.

Silicone moulds and plugs

Silicone moulds have good release properties, but their release performance can reduce with repeated use. We recommend applying a suitable mould release before each casting.

Our silicone moulds can be preheated and casts can be post-cured in the mould. Although the silicone moulds can withstand temperatures of 120°C (250°F) or more, the HDPE plugs used with our Less-Resin moulds should not exceed 60°C (140°F).

Take care during de-moulding not to overstretch the silicone or damage it with sharp edges on a cast. After use, remove resin residue with warm soapy water. Stubborn residue can be treated carefully with a small amount of denatured alcohol or acetone on a soft cloth. Dry the mould and allow it to dry completely before reuse.

Store silicone moulds flat to reduce the risk of deformation. Do not leave the plugs fitted in Less-Resin moulds during storage because this can stretch the holes over time.

Browse our Silicone Casting Moulds.

Using Less-Resin mould plugs

Insert a plug into one hole in the mould and slide the tube onto the end of the plug. Insert the second plug through the opposite hole and push it into the other end of the tube. Check that there is an even gap between the tube and each end of the mould.

Apply reasonable inward pressure to the plugs with your index fingers. While maintaining that pressure, use your thumbs inside the mould to pull the mould walls slightly outwards. This helps create a snug fit and reduce resin seepage.

If casting only one blank, the centre tab can be temporarily filled with a small piece of plasticine/modelling clay or a resin tab saved from a previous casting. To remove the plugs, twist them to break the seal and pull them out carefully.

See our Less-Resin Casting Moulds.

DIY Vaseline mould release

We have found a Vaseline-based mould release useful with both our silicone and HDPE moulds.

Mix approximately 1 part Vaseline/petroleum jelly with 10–15 parts white spirit in a suitable airtight container. To help dissolve the Vaseline, place the closed container in hot, not boiling, water and shake it periodically. White spirit is highly flammable, so keep it away from flames, sparks and other ignition sources and follow the product safety instructions.

The mixture can separate while standing; shake it thoroughly before use. Apply a thin coating to the mould and plugs with a brush, then allow the white spirit to evaporate fully before casting. Work with appropriate ventilation and follow the safety instructions for the materials you are using.

For more resin-casting information, visit our Resin Casting Supplies & Guides hub. For pen-turning information, see our Pen Making Guides.