Why SLA prints can poison the silicone

SLA print resins are often epoxy resins. These result in cure inhibition of your addition-curing silicones, also known as platinum silicones. This is also called cure inhibition, curing inhibition or silicone poisoning.

This can be prevented by ensuring the 3D print is fully clean and fully cured. Even better is to apply a sealing layer such as PVA (polyvinyl alcohol) or a varnish that does not cause cure inhibition.

SLA post-processing guide for 3D printing

Below are the seven parts of good post-processing, from removing the print to making it waterproof. Go through them in order for the best result.

1. Remove the print

Carefully remove your SLA print from the build platform. Wear nitrile gloves and safety goggles to protect yourself against uncured resin. Carefully place a plastic or metal scraper under the edges of the print and apply even pressure to release the print from the platform without damaging it. If the scraper method is difficult, you can carefully twist the build platform to reduce the pressure.

2. Remove supports

Use a flush cutter to cut the supports close to the print surface. Be careful to avoid deep gouges. After cutting, sand the remaining nubs with fine sandpaper of about grit 220. For a smoother finish, gradually move to higher grits such as 400 and 800.

3. Wash

Washing is crucial to remove uncured resin and prepare the print for curing. Immerse the print in a container of isopropyl alcohol (IPA) of at least 90% and stir gently so all surfaces are washed. If available, use a wash station with a rotating basket or magnetic stirrer for a more thorough cleaning. After washing, rinse the print with clean IPA and let it air dry completely before continuing.

4. Cure

Curing solidifies the resin and improves the properties of the print. Place the print in a UV curing station for even curing and keep to the manufacturer's recommended curing time, usually around 10 to 15 minutes. If you do not have a curing station, you can of course use sunlight. Then expose the print to direct sunlight for several hours and turn it regularly for even curing.

5. Sand and polish

Start sanding with a lower grit, for example 220, to remove rough spots or support marks. Gradually move to higher grits such as 400, 800 and up to 1500 for a super smooth finish. Wet sanding can help achieve an even finer finish; use water to lubricate the sandpaper. For a glossy finish, use a plastic polishing paste with a soft cloth or a rotary tool with a polishing pad.

6. Paint

Start with a primer so the paint adheres better. Spray primers work well for even coverage. Then use acrylic paint in thin, even layers and let each layer dry before applying the next. For finer details use small brushes or airbrush techniques.

7. Make waterproof

Protect your print with a sealing layer. Choose a clear varnish or UV-resistant sealant to protect the print against external influences. Make sure the coating does not cause cure inhibition for platinum silicones. Spray or brush the sealer in even layers and let each layer dry before adding a new one. Let the print fully cure after sealing for maximum durability.

Absolute certainty

If you follow these steps, you have a good chance of a 3D print that does not cause cure inhibition with addition silicones. However, we cannot give a full guarantee. If you want absolute certainty that your 3D print does not hinder curing, you can:

• Use a different 3D printer that works with PLA, or
• Choose a different silicone based on condensation curing.