Mould Care and Use with Resins
Updated: Jan 11
All silicone moulds do wear out eventually for a variety of reasons, and some will loose their shine sooner then others as well, and become more dull over time. But there are ways to take care of a mould so it will last longer, and keep its shine longer.
SHINY AND MATTE MOULDS
There are many types of moulds used in resin projects. When purchasing a mould, remember that if it has a shiny side where resin will be poured, the piece will come out shiny too. If it is matte/dull, the resin piece will also come out dull/matte. Some of the less expensive moulds may deteriorate sooner, but they can also be a good way to learn and start your resin casting journey off more economically.
If your piece comes out matte, and you want it shiny, you can dome coat it (top coat with resin), or brush resin over it to bring the shine out. Ideally, if you want a shiny finish, always purchase a shiny mould to begin with. Or another option is to sand & polish the piece to a glasslike shine.
THINGS THAT DESTROY YOUR MOULDS FASTER
Torching is a popular way to pop bubbles in resin (on flat surfaces like wall art & tables), but it can cause the silicone to fuse to the resin piece when torching in moulds. It will tear and ruin your mould. Although many silicone baking moulds can tolerate oven & high heat, they typically always come with instructions stating "not to use with direct flame". Never ever use large torches with small silicone moulds. Kitchen or chefs torches can be too direct a flame and too hot at it's point. A chefs torch turned down low, could be used once you know how to manipulate it so it doesn't ruin your moulds or scorch your resin. Ideally, It's best to use as low a flame as possible, but don't let the flame touch your resin or mould. Barbecue lighters with adjustable flame setting, are more suited for the moulds, as the flame is often not as strong or as pointed as the chefs torch . Try to find the type of barbecue lighter you can adjust the flame setting on. Keep the flame high above the piece, and never go near the mould. It's actually the co2 from the lighter (flame) that is popping the bubbles so you don't need to ever touch flame to the resin or mould. You can use a silicone brush, spatula, toothpick or sewing needle to pop bubbles, and to push bubbles away from the edge. You can heat up a sewing needle or pin to help pop bubbles once they're away from the edge. Heat guns are often also suggested to reduce bubbles, but they too can cause overheating, & fusion of moulds to resin, plus the added air flow may move your resin out of a design you’ve made, so be careful with those too. Craft embossing hot air guns are also often used. Each artist tends to find their own preference after experience and they type of projects they create.
Some artists will suggest and swear by using isopropyl alcohol, in a fine spray mist, to pop bubbles instead of heat, and it can work. However, just be aware some resin manufacturers do not recommend that. If too much alcohol is sprayed it might affect the cure negatively, and it can break down the Epoxy where it contacts. If you choose to spray alcohol, it is at your own risk to project, and be aware that it "could" produce an undesireable cure finish. Using isoprophyl alcohol seems to be becoming a popular method for popping bubbles in resin when people are not familiar with how to control the heat (barbecue lighter) method. Tinier moulds would be hardest to torch, so the alcohol spritz is most common when working in small sizes.
Use a VERY fine mister spray, when spritzing because if the alcohol droplets are too big or too close, they can leave pinholes or other marks in the resin once cured. Some users say the alcohol will pop the surface bubbles, but you may have to do it multiple times, like every 15 minutes (set a timer), for an hour depending on resin being used (and if any inclusions are sending bubbles up too). If using alcohol misting methods, the alcohol needs to be higher percentage alcohol content 99% is ideal (it has the least amount of water content, but some do use 91%). If you've sprayed alcohol over your resin, do not use a flame right after, as alcohol has to have time to dissipate first, to reduce risk of starting a fire. Also note: Alcohol is drying to moulds, and can shorten life of moulds. Some custom silicone mold makers discourage use of alcohol on their moulds.
If creating with alcohol inks, (petri effect or as a colourant), be prepared they can participate in reducing the life of your mould as well, since they are alcohol based. There are lightfast transparent resin tints (Colour Passion & LeRez Expressions make them), that are not alcohol based, and they also don't fade like alcohol inks can. If you want a transparent colour, they will be less damaging to your moulds then the alcohol inks.
Using crushed glass, glitters, rocks or any hard inclusions may cut, scratch or mark your moulds, so if using, be aware when using them up against mould surfaces.
Also, please note: when using a brush to paint pigment powders on to the moulds prior to pouring resin, be gentle & extra careful not to let brush edges scratch your mould (scratches will show up in castings). Same consideration with using paint markers, pens or other tools to add details on moulds prior to pouring resin. If mould gets scratched or indented anywhere, that will transfer to all future castings in that mould.
Ideally, you want to learn to reduce potential for bubbles prior to pouring resin in the moulds. One key thing you can do, is ensure the resin is not cold, and has no to low bubbles prior to pouring in to the mould. Use silicone, metal or plastic utensil to stir instead of wooden sticks (some wood is porous can release air in to resin when stirring). Stir thoroughly, but not vigorously, a moderate stir, scrape sides and bottom now & then. Pour slowly into mould, and some people like to pour down the edge of the stirring tool into the mould to reduce adding bubbles while pouring. Or you can pour along side/edge of mould. There is a separate blog post about reducing bubbles.
Overheating Resins can also cause added issues for mould life. Excessive heat from overheating resin can also cause your mould to become dull prematurely. If a resin is poured past it's depth threshold, or organics added that create overheating or moisture (due to not being dried thoroughly or other possible contaminants), or too much colourant added to create overheating, or resin that started it's cure in mix cup (sitting too long) prior to being poured in mould, can cause premature exotherm, and overheat in mould. If resin goes into pre-mature exotherm, it can get extremely hot, which can fuse resin to the moulds too. Pre-mature exotherm can also cause resin to pre-maturely exotherm, & cause it to be fragile & crack easily.
Casting resins such as iCoat's CE4100HV, TP21, TP24 FC, and Depth, are specifically designed for use in moulds, and yield best results when used according to each resins suggestions. Many projects require pouring in layers, so the resin does not overheat. There is lots of information available about working with all our resins in their information pages or on our blog pages, on our website. I have a very long (older) Blog post also on website, called "All About Working with Resin Guide" full of helpful tips.
Top-coating, art resins, counter and other types of non-casting resins, were not designed for use in moulds, however if mould is shallow enough, they can be used. Many artists use them because it's what they have on hand, or for the quicker cure times, different viscosity preferences for certain techniques, etc. Sometimes the countertop type resins are better suited for very shallow molds where project requires a non-bendy resin (such as wine-caddies, cell phone holders, rulers, bookmarks, etc.).
Top-coating resins often cures in half (or sooner) the time of many Casting Resins, so some people prefer them for their shallow (less then 1/4" pours). Topcoating resins typically need to be poured in numerous shallow layers of less than 1/4" each time and layer. With some casting resins,
With some types of casting resins (not all), they suggest you let it sit in cups for 5-10 minutes after mixing part A & B, before pouring in to moulds to help degassing of bubbles. With countertop/topcoating/art resins, it’s the oppposite, and it is recommended not to allow resin to sit in mix cup before pouring into moulds, but it can sit a bit (5 minutes is fine if spread in to smaller cups) to help degas bubbles. Just keep an eye on resin, make sure it doesn't sit too long that it gets hot.
Once the two parts of a resin kit are mixed together, they do begin their cure cycle (even while sitting in the cup). Countertop/topcoating resins with it's thicker viscosity, is meant to be poured on to surface areas shortly after mixing, so a premature exothermic reaction doesn't start to occur in the cup. If resin is getting warm in the cup, it has been left to sit too long (or if colour was used, the ratio of colour added may have been to high). Adding too much colourant (over 8-10% ratio to resin, can also cause resins to go into premature exotherm as well.
Larger resin mixes will cure faster, and smaller mixes and shallower moulds will cure slower and take longer. Cure times will vary depending on mass and temperatures and additives & mould shapes. With some basic 2:1 casting resins, a 30 gram (2-3 oz mass) is roughly about 16-24 hours based on room temperature of 77F (25 celsius), so if room is colder, it can take longer to cure. For lower amounts and lower temperatures, it will take longer to cure. Also, please note, that mould shapes can effect the process too. Spheres for example, (or any more enclosed type mould) will hold in the heat more, and may need to be poured differently with more layers then a mould that is wide open and doesn't hold the heat in.
When working with your moulds, keep the ones you use for resin, for resin only. Do not use them for any other projects. Once moulds are worn out, and shine is gone, you can repurpose them for concrete or other non resin casting type projects if desired. Or you can continue to use the mould, but be prepared to sand & polish the piece to a glass shine if desired.
Try not to stretch your moulds too far when removing objects, as it can also wear down the shiny surface or tear the mould. When trying to remove resin cast pieces from your mould, try running a bit of water and mild dish soap between mould and piece, and slowly work it down to help gently release the piece.
There are mould release agents some people like to use. They sometimes come in different sheens (matte, glossy etc), so make sure you check the sheen level too if that manufacturer has that option. Your experience may differ from anothers, so sometimes trial and error is best way to see what your own preference will be. Be aware some people have found mould release agents left marks on their resin projects. It may need to be applied by dabbing/tapping it on with a soft cloth instead of spraying so it's more uniformly applied. Or, another consideration, is it's possible if it's leaving marks, it just may not be compatible.
WASHING YOUR MOULDS
Basically silicone (which many moulds are made of), at its core is an oil, and anything that fights grease/oil will eat away at it. Soaps that cut grease & alcohol is very drying. Even when you pull out a cured piece, it pulls some of the oils out with it. Each use, will pull a bit more again. So conditioning your moulds is a thing according to some people (not all). It could possibly help them last a little or a lot longer.
When washing or cleaning our your moulds, try not to use your nails or harsh scrubs or scrape, or anything abrasive to remove items from them. Don't ever rub your moulds, or use anything that might scratch them, as that will translate over on to your next piece casted. Many people use tape to remove dried resin from moulds that is stuck in spots. Alcohol can also deteriorate moulds sooner, so never use alcohol to clean or wipe your moulds.
Some silicone mold makers prefer you not wash your moulds, (if at all possible), just use tape to get anything out that may be in there.
One method I recently heard of to wash (if it's really needed), is to use a very gentle foaming (non abrasive or harsh) soap to wash all the moulds in a bucket with luke warm water. Then pour the water out, rinse a few times and add a clean fill of water, and a couple drops of baby oil on the surface (more moulds, more oil), swish it around and let it settle on the surface, as you pull the moulds out a thin layer of oil will coat each mould. (an oil bath) Let them air dry with the crevice upside down to how you would cure resin. With this method, you will need to check if your resin cure might be effected by the baby oil. To check if baby oil will be an issue, get a non stick surface such as a silicone mat, or an old mould, rub some baby oil on it, and just a drop of resin from a batch you're using anyway (this then becomes a control sample as well). If it sets & cures like normal on both pieces then you should be fine with baby oil as a conditioner for your moulds as per above method. If neither the test nor the project item set or cure right, then you know it's more the mix. But if your project sets & cures correctly, but the test part on mat or old mould won't set over baby oil, you'll know you can not use that method to condition.
*Important note: Every resin brand is made up of it's own very sensitive chemical blend, that can be thrown off by adding something that may effect cure. So a controlled test is helpful to know what will work with your preferred brands.
Another different method some people use, if their mold really requires washing out due to certain items sticking to it, is to make a slurry of baking soda, distilled water, a tiny bit of vinegar, and a drop of very mild dishsoap (nothing with grease cutters in it). Use the gentle slurry to try rub bits off that are stuck on the mould. Then air dry. The distilled water is suggested so no hard water marks are left when drying.
Some artists suggest that on quality made silicone moulds, you can use a silicone conditioner, or 100% silicone oil (bicycle lubricant), on your moulds to help keep them conditioned between use. Gently, dab it all over, and let sit for a few days to fully absorb and recondition. It can potentially help prevent your mould from drying out faster. When you do this though, you will need to allow the mould to rest between castings, so the oil fully evaporates before next casting, so don't do this until you can give your mould a several day break from use. If there are pools of oil anywhere, you may need to use a soft cloth to gently dab it off. Again, with this option, you will need to do a small test (mentioned above), with chosen oil and your resin.
STORING YOUR MOULDS
Storing your moulds properly also helps keep their condition & shape in best form. Never store in open air. Many people keep the original packaging moulds are shipped in, to store them as well. Some people use ziplock bags or saran wrap. User a marker to write on the plastic, which mold the packing belongs to, for ease of reuse. While you're at it, if really organized, you could also write the amount of resin required for that mould on the package. Once wrapped, some people store in plastic drawers, boxes or shelves. Another storage option for some mould styles, if you have hanging space, is to clip the ziplock bags (holding the moulds), to pant hangers (like plastic Walmart ones they throw out).
If you have space you can store in a chest of drawers by theme. Store in a cabinet on shelves for the big ones that have to lay flat. For really small moulds, you can use those units with little drawers they use for nails and small tools.
Just be sure once wrapped, moulds are protected from also getting crushed or bent, warped or marked in storage, because it permanently effects their shape.
Happy casting and I hope this info might help prolong the life and condition of your moulds. :)
This image below: shows a mould on the left, that has worn out. The shine is gone (mould is actually faded), and the edges have relaxed and no longer hold the shape. The image on the right, shows a mould that still has it's shine (can not see in photo), and the edges are still firm and supportive.
Here is another example of a mould that has worn out. These are the exact same mould from same supplier, and same silicone material. The feather mould on the left had been used twice. The feather mould on the right had been used about 15 times. So as you can see it's getting pretty worn , from both resin, as well as being stretched many times to release castings.