Friday, August 21, 2020

How to Care for Resin Moulds

After you've been resin crafting for a while, you'll start to get quite a collection of moulds. Your resin moulds are an investment in your resin hobby so you want to make sure that they last a long time. 

No matter what type of moulds you have - silicone, plastic, ice cube moulds, clay moulds, soap moulds - they won't last forever. But if you know how to look after them, you'll get many, many casts from them.
Round blue silicone mould broken in half

So, let's break this down into the two main types of moulds you'll use with resin

and look at what the best practices are for caring for each type of mould.

Silicone Moulds

Silicone moulds are the best thing since sliced bread and will take your resin casting to a whole new level!

Why are they so good? 
  • resin doesn't stick to them... 
  • they're flexible and SO easy to demould... 
  • they come in every shape and size you can think of
  • silicone moulds last a really long time and you'll get a lot of castings from them.

You can buy them or make them yourself with silicone putty or silicone rubber. And yes, you can even use silicone ice cube trays and cake decorating moulds which come in an enormous array of fun designs! 
An assortment of colourful ice cube and cake decorating silicone moulds

But once a silicone mould has been used for resin, it can no longer be used for food.

Silicone has amazing NON-STICK properties so it isn't necessary to spray moulds with a spray release before filling them with resin. 

But spraying your moulds with a release agent conditions the moulds so you get a few extra pulls from them. Think of mould release in the same way as using moisturiser on your skin... mould release conditions your moulds in the same way.

Cleaning Silicone Moulds

Anything left on the surface of your silicone mould will be permanently embedded in your next resin casting, so cleaning them regularly is essential. Here are my TOP TIPS for cleaning them.

Tip No. 1 - Use Adhesive Tape

Silicone moulds attract dust, fluff and pet hair. 

And some of the mix-ins you use, such as glitter, mica powder and metal leaf flakes will also stick to the silicone. 

You'll need to clean all these things off your moulds before pouring the resin, or that stray pet hair or fleck of glitter will permanently become part of your resin! 

Adhesive tape makes short work of cleaning the silicone. 

Just dab a piece of tape across the stray bits and it will clean up your mould in no time. This is my preferred way to clean silicone moulds. 

For more detailed instructions, see this article on How to clean silicone moulds
Grubby gum leaf shaped silicone mould

Tip No. 2 - Wash Silicone Moulds with Dishwashing Liquid and Water

Adhesive tape is great for cleaning off the stray bits that stick to the silicone. But there are times when you need to wash the moulds with soap and water. 

If you use your moulds with multiple resin types, say epoxy one day, and polyurethane or UV resin the next, chemical residue is left behind. 

Even though these residues are invisible, the chemicals will react with each other and cause the silicone to degrade faster than if you only use one resin type in your mould. So cleaning away that residue will extend its lifespan. 

Washing moulds is simple to do. 

Just use a mild dishwashing liquid and water and smear it around the entire inside surface of the mould with your hands. Avoid using anything abrasive such as steel wool, nylon sponges or toothbrushes as these scratch the silicone and permanently damage them. 

Wash away the soapy liquid and pat dry with a lint-free cloth. 

For moulds with an enclosed shape (like a bangle mould), it's easier to leave the mould upside down to drain on the sink than to try to pat it dry. Leave the mould to fully dry before pouring resin into it.

Tip No. 3 - Use Baby Wipes to Clean Off Mica Powder

Baby wipes are really handy when you need to clean things up quickly. They will easily wipe away mica powder. Try to use wipes with no alcohol in them as repeated use with alcohol-based wipes eventually dulls the silicone surface and you'll lose that lovely glossy shine that we all love in resin. 

Things that Destroy Silicone Moulds

1. Copious Amounts of Alcohol Ink

The Petri Dish technique is a great technique that reveals fascinating tendrils of colour inside the resin. 

This technique has also given rise to an untold number of torn silicone moulds across the globe!  
Rainbow coloured petri dish coaster viewed from side on

The copious quantities of alcohol ink used to achieve this effect lead to the silicone breaking down very quickly. You can extend the life of these coaster-type moulds by spraying with mould release. But in the end, you will have to replace the mould. 

Tip: Even though the alcohol ink leaves a stain on the silicone, the colour doesn't leach onto your next project.

2. Excessive Heat

Another process that breaks silicone down quickly is the application of EXCESSIVE HEAT. 

A BBQ torch or gas lighter passed quickly over the surface of the resin to pop bubbles won't damage the silicone. 

The trick with a lighter is to not hold the flame in one place. If you hold the flame in one place too long, it heats the resin and then it fuses to the silicone... permanently.

But using a butane torch (such as those used in resin art) is overkill for small moulds. Even a small chef's torch has too much heat to be used in moulds.

Silicone moulds can handle being in an oven at temperatures of up to 205°C (400°F) but the heat from the flame of a chef's torch or a butane torch is much higher. 

Excessively heating the silicone causes the resin to bond to the silicone making it impossible to remove from the mould without tearing it.
Red cross mark through a chef's culinary torch and a small butane torch

3. Resin... Yes, Resin!

If you're using UV resin, you might have noticed that clear moulds don't last forever. In fact, you might have noticed that clear moulds don't stay clear for very long... they soon turn cloudy or milky white.
4 slender crystal moulds showing signs of turning from clear to white as they age

UV resin gets quite warm as it cures. So this is a combination of the UV resin and the heat generated from the UV lamp breaking down the silicone. 

This also happens when you use epoxy resin in the mould. You can't avoid the heat build-up - it's part of the curing process.

Epoxy resin is a very "grabby" resin, so each time you demould the resin, it pulls at the silicone and microscopically damages the mould. Over time, this leads to the silicone surface breaking down.

4. Sunlight

Sunlight contains UV light and we've already covered how UV lamps can damage silicone. So it makes sense to protect your moulds from sunlight. 

Keep your moulds out of direct light when they're not in use. 

Store them in a box, a drawer, or anywhere that will keep them from being exposed to sunlight. It will also keep dust, fluff and other debris from collecting on them in between uses. 
Flat drawers filled with pink and blue resin bangle moulds

Sadly, your moulds will eventually deteriorate and at some point, you will need to replace your silicone moulds.
A round blue mould broken in half

 As the silicone begins to deteriorate, you might notice some of these signs:
  • The mould surface becomes really smooth to the touch, instead of having that "grippy" feel about it
  • Shiny moulds lose their shine and your future castings are matte or dull 
  • The detail of the mould begins to feel hard and crusty instead of springy to the touch
  • Resin doesn't release easily from the silicone even though it's cured
  • Some of the silicone comes out with the resin or the silicone tears as you try to demould it (this mould is DEAD!)
At that point, you might get one or two more pulls from the mould if you spray it with mould release before filling it with resin.

How to Demould Resin from Silicone Moulds

When it comes to demoulding resin from silicone moulds, you just need to gently pull the silicone away from the resin all the way around the mould. 

Moulds with a wide opening are easy to demould. But some moulds are a little trickier to get the resin out of, like the popular cylinder and wand-style crystal moulds. 

A little bit of liquid soap and some water to lubricate the top of the mould will break the vacuum seal between the resin and silicone and make the resin slide right out. Watch this short video to see how to demould resin from slender moulds in action.
Hand under running water removing slender resin crystal from a silicone mould

Plastic Resin Moulds

Plastic resin moulds are inexpensive compared to silicone moulds but because they are vacuum formed, mould shapes are limited to simple shapes. Plastic moulds have no stretch and they don't have as much flexibility as silicone so they need to be wider at the top of the mould or straight-sided to remove resin from them.
Selection of plastic resin moulds in a pile

The plastic used in resin moulds is polypropylene. This is a type of plastic that resin doesn't stick to so it's ideal for resin moulds. 

Plastic resin moulds are made from a thicker, sturdier plastic than the moulds used for other crafts such as candy making. 

Plastic moulds made for other crafts are generally not suitable for resin because

... they are made of a type of plastic that resin sticks to 

... and they can't withstand the heat generated by resin as it cures. 

Plastic moulds can easily be damaged so you need to take care when working with them. 

You have to twist the mould to release the resin cabochons but you need to be careful not to damage the mould when you push the castings out. 

It's tempting to push the cabochons out but pushing with force can cause a dent that looks like a white line in the plastic. Marks like that will show in the next piece you cast in the mould. And so do any scratches, so keep sharp objects away from the cavities of the mould.

Tips for demoulding resin from plastic moulds

1. Spray the Mould with Mould Release

Even though resin moulds are made from polypropylene, I recommend spraying the mould with mould release before casting with resin. You can use either a pressure can or pump spray. 

This simple step can make all the difference between an easy demould and having a difficult time getting the resin out of the mould. Let the mould release dry before pouring resin into the mould.
Plastic resin mould being sprayed with mould release

2. Wait for the Resin to Cure

Don't try to demould resin from plastic moulds until they have reached "soft cure". This is generally around 24 hours for epoxy resin. Some epoxies take longer and some are shorter but go by what the instructions in your resin kit say.
24 hour clock

3. Flex the Mould to Break the Seal

To demould your cabochons or bracelets from plastic moulds, you'll need to flex the mould to break the seal between the resin and the plastic as if you were trying to release ice from an ice cube tray. 

When the resin starts to release, you'll notice that an air pocket begins to open up between the two and once that happens, just keep working your way around the mould, flexing it as you go until the air pocket is all the way around the resin. Then you can press the back of the mould to pop the cabochon out.
An air pocket opening up between the resin and plastic mould

4. Tap the Mould on the Bench

If flexing the mould didn't release your casting, you can give it a few short, sharp taps on the bench. This can sometimes release the resin from the plastic. Remember that your mould is plastic, and plastic can break. If you tap too hard like I did, the mould can snap!
Broken plastic drawer knob mould

5. Place the Mould in the Freezer

This last tip is my favourite trick for releasing resin from plastic moulds. 

Place the mould in the freezer for between 10 and 30 minutes. This causes the resin to contract and in most cases, it releases from the plastic mould really easily. 

Expert tip: Place the mould in a freezer bag and seal it so that you don't risk contaminating food in the freezer.
Plastic resin tray on freezer shelf

 Expert tip: Once you've demoulded all your resin pieces from the mould, spray it with mould release BEFORE putting it away. This way, you'll be able to pour resin at your next resin casting session without having to wait for the mould release to dry!

How to Store Plastic Moulds

Plastic resin moulds can warp or bow if they're not stored flat. And I can tell you from experience that a warped mould is very difficult to work with! Once they're bowed like this one, it's impossible to get them flat again.
Warped plastic resin mould

This pour mould got buried amongst a pile of other things in the heat of summer and it wasn't sitting flat. I soon realised that I'd need to find a better way of storing moulds and this is the system I came up with:

1. After spraying my plastic moulds with mould release, I let them dry and then place them in a zip lock bag to keep the dust and lint away. I also slip a Post-it Note inside the bag that reads "SPRAYED".
Inserting a sprayed plastic mould into a ziplock bag

For those that are the same shape, I line up the cavities so that the moulds nestle inside each other (these are all placed in a single zip lock bag). The weight of those on top helps keep ALL the moulds flat.
A stack of sprayed plastic mould trays inside a ziplock bag

2. I stack them all in layers in a plastic tub with a sheet of corrugated cardboard or matt board between each layer of moulds. Try to group moulds of the same dimensions in each layer. 

3. I prefer to store them stacked horizontally but if your storage space dictates that you must store them vertically, sandwich them between two layers of firm cardboard and secure them with elastic bands so they don't bow. For larger moulds where an elastic band would be too tight, use a length of hat elastic and tie it into a knot. 
Inserting a plastic mould sandwiched in corrugated cardboard into a plastic tub

4. Keep them in a cool place, away from sunlight as UV can break plastic down over time.  

Using Other Types of Plastic Moulds

If you decide to take a chance on a plastic soap mould, blister packaging or a chocolate mould, spray it well with mould release. Sometimes, they actually work! 
An assortment of plastic blister packaging

Even so, these types of plastics will only make short-term moulds but they can be fun while they last. So, hope for the best but be prepared for the worst... if you can't get the resin out of the mould, not only have you ruined the mould, you've wasted your resin too. 

Oh, and one more thing about using moulds from the kitchen, once a mould has had resin in it, it can no longer be used for food.

Pin This!

Inspiration sheet featuring a collection of colourful moulds

Happy Resining!

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Would you like to comment?

  1. Hi there. My first attempt at a large pyramid has left layer lines around the silicon mould. Please could you tell me what has caused this and if they will show up on future casts? Many thanks 😊

    1. Hi Cheryl.
      When working with multiple layers, you need to pour each successive layer before the previous layer of resin has cured.


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