Monday, April 19, 2021

How Long Do Silicone Resin Moulds Last?

How long does a silicone mould last? And how many pieces will I be able to cast from it?

These 2 questions pop up a lot. Unfortunately, there's no definitive answer and it's a bit like asking how long is a piece of string?

But one thing's for sure... SILICONE MOULDS ARE PERISHABLE and they won't last forever. 

From time to time, you will have to replace them. And whilst that can be devastating when a favourite mould wears out, I can't think of a better reason to buy a new design to add to your collection!

There are many reasons why resin moulds perish but there are also a few things you can do to extend their life so you can get maximum value from them.

But did you know that the cause for the deterioration of many of your moulds is actually the way you use them? 

Those popular techniques with alcohol ink and the handy bubble-busting tips with heat guns, they're actually the things that shorten the life span of a silicone mould. 

Want to find out some other things that you're doing to your moulds that shortens their life span?

Then read on to learn more about what those causes are and the steps you can take to make your moulds last longer.

1. Using Epoxy Resin 

Yes, that's right! Epoxy resin is very aggressive towards silicone, much more so than other types of resin. Epoxy "grabs" the silicone, and with each casting in the mould, the chemicals in the epoxy formula cause the silicone to degrade a little. You won't even notice it at first but in time, the silicone will lose that slightly moist feeling OR become super smooth and lose its ability to release the resin.

2. Using the mould with multiple types of resin

I'm totally guilty of this one. In the studio, I switch between epoxy resin and polyurethane resin in my silicone moulds without cleaning them and each resin type leaves minute traces of chemical residue behind on the moulds. Together, those chemicals "eat away" at the silicone faster than if I stuck with just one resin type.

3. Excessive Amounts of Alcohol 

That means rubbing alcohol, methylated spirits (denatured alcohol) AND alcohol inks. 

Alcohol removes the shine from your moulds and dries the silicone out, so if you're spritzing the bottom of your mould with rubbing alcohol to minimise bubbles, or cleaning your moulds with alcohol, that will shorten the life of your mould. 

And too much alcohol ink mixed into the resin will fuse the resin to the silicone (think petri dish technique). By the way, that happens whether you're using silicone OR plastic moulds.
Dripping yellow alcohol ink on top of white alcohol ink onto the surface of resin in an oval shaped plastic cabochon mould.

All types of alcohol will dry out the silicone in time. Alcohol is best reserved for popping surface bubbles where the only silicone that comes into contact with the alcohol is the outside of the mould. 

4. Heat - Using Heatguns, Torches and Lighters

Using a long-neck lighter to pop bubbles in multi-coloured resin bars

It's common resin advice to use a heat source for popping bubbles on the surface of resin. It works a treat! 

But when too much heat is applied, the resin can fuse to the silicone and the only way to demould the resin will be to destroy the mould.

Silicone can generally withstand moderate oven temperatures (think of your silicone bakeware) but the heat from a heat gun is considerably higher. 

The same goes for flames from BBQ lighters and chef's torches. The heat from both of these sources is way too high for silicone. It doesn't mean you can't use these tools for popping bubbles, but the high temperatures they put out will cause the release properties of silicone to eventually fail. 

If you choose to use a BBQ lighter, then first, use a toothpick to drag all the bubbles away from the silicone edges towards the centre of the resin. Then you can wave the heat source across the bubbles very briefly, well away from the edge of the mould.  

But there's another source of heat that isn't quite so obvious. Resin itself generates heat as it cures. For small casts, the amount of heat generated won't do any harm. But when you're using a deep mould with a large volume, the amount of heat generated by say 1.2 litres (40oz) of resin can cause the epoxy to fuse to the silicone. 

So for deep moulds like pyramids that take a large volume of resin, pour the resin in layers and allow the resin to cure before adding the next layer so that the heat has dissipated. 
resin pyramid filled with layers of avocado, gold metal leaf and black resin sitting on a glossy black table

You'll usually find information about the maximum amounts of resin to mix, and maximum depths to pour, in the instructions that come with your resin kit.

If you don't want to pour in layers, choose a resin designed for deep pours. These resins take longer to cure because less heat is produced so it is much kinder on your mould.


Now that you know the things that can break down your silicone moulds, you can minimise a lot of the damage by avoiding those situations. Obviously, you can't eliminate resin, but you can limit the impact of the other factors.

Here are some things you can do to get more life from your moulds.

1. Store Your Moulds Clean and Flat

  • Anything that stays in contact with the mould for an extended period of time has the potential to damage it. Even something as small as a fleck of chunky glitter or a drip of resin that's cured can leave a permanent indentation on the surface of the silicone. 
It's particularly noticeable on cheap silicone moulds. If you leave drips to cure inside the mould shape, the indentation they leave behind will show up on every casting. So make sure you remove anything that is sticking to the surface of the mould. Here's a quick and easy way to remove stray bits of glitter, mica powder, dust and pet hair

Take care when using pointed objects to dislodge glitter or other particles because even something as innocent as a toothpick can scratch the mould permanently or easily poke a hole in it (speaking from experience here!) that resin will leak out from.
  • Store your lightweight moulds flat, in a single layer, so they don't get crushed or misshapen. 
  • Storing them with a casting in them will help them keep their shape if they are stored for a long time.
  • Moulds with thick walls can be stacked in layers
  • Hand wash them with mild liquid soap and water in a dedicated bowl to remove the chemical residue left behind from the resin. Make sure you rinse off all the soap and leave them to air dry on a cloth. If you need to use them again straight away, use a lint-free cloth to dry them. 
Tip: Don't be tempted to put them in the dishwasher even if the moulds you're using were originally intended for food. Just because it says it's dishwasher safe, you really don't want to put a mould that's had resin in it into the dishwasher.
  • Always avoid harsh chemicals or anything abrasive like a scourer or toothbrush as these can scratch the silicone surface permanently. 


2. Use a Mould Release 

When silicone moulds are brand new, they still have some release agent on their surface from the manufacturing process. This release agent lasts for a few castings which is why it's so easy to demould your first few resin casts from a new mould. Once it's worn away, you can spray the mould with a mould release so that it continues to release your resin castings easily. You can do this every few casts throughout the life of the mould.
Pink silicone mould being sprayed with mould release

I like Castin'Craft's Mold Release and Conditioner because it has the added benefit of being a mould conditioner too and that helps extend the life of your mould even further.

3. Treat Your Mould Gently When You're Demoulding

Silicone has flexibility and also a small amount of elasticity. Even still, take care not to overstretch your mould when you're pulling your resin casting from it. Overstretching it will break down the inner surface of the mould and cause micro-tears in the mould cavity that will appear as imperfections on your next casting. It also causes the silicone to lose its glossy finish so all your future castings will look a bit dull. 
Dull, white splotches on the interior of a pink silicone mould from overstretching it.

Even with the elasticity of silicone, tears can happen at the top of the mould if the opening is narrower than the width of the resin inside the mould. Orb and dice moulds are good examples of moulds that taper towards the top. 
Resin orb filled with red carnation petal sitting on top of a clear silicone orb mould and another resin orb bead sitting between the two silicone moulds.

Try not to put any undue stress on the openings of these types of moulds when demoulding. Stretch the top slightly whilst simultaneously pushing the resin up from the bottom of the mould to ease the casting out.
Demoulding an orb from a silicone mould by pulling back from the top and simultaneously pushing up from the bottom

So there you have it.

You've invested a lot of money in your moulds and with proper care, your moulds will last a long time. 

But try to think of them as consumables, just like resin: when you run out of resin, you have to replace it; when your mould breaks down, you need a new one.

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Spritzing a pink silicone ring mould with mould release spray

Happy Resining!

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