Bubbles in resin

Bubbles are the nemesis of all resin crafters- while they can sometimes be used for interesting artistic effects, in most cases they’re just an annoyance that prevents you from making what you intended to. This post will cover both how to avoid bubbles in the first place and how to go about removing the ones that sneak in anyway.

Avoiding bubbles while mixing

Most resins will have a small amount of air mixed in already, but you can avoid adding more bubbles with a few simple steps. To start, when pouring the resin from its storage container into your mixing cup, avoid just pouring it into the middle of the cup- otherwise once you have a layer of resin it can start to pull air down into the resin and make bubbles. Instead, try to pour your resin down the side of the cup and you should find it fills up without adding bubbles to the mix. The same can be done with the hardener, but it will depend on your resin as to whether it’s needed (thinner hardeners are less likely to be problematic).

Next, when mixing your resin it’s important to choose a non-porous implement to mix with. Popsicle sticks are commonly recommended because they’re cheap, easy to get, and have a good surface area, but this comes at a cost. Air can leech from the wood and into your resin resulting in micro-bubbles throughout it. Anything non-porous will do, but I prefer to mix with a mini baking spatula as they’re generally made from either silicone or plastic and have a good surface area to help ensure your resin gets mixed properly. For smaller amounts of resin or to mix in colours I also use a cheap plastic paintbrush handle, the round shape seems to help somewhat in avoiding bubbles.

So we’ve got our resin in the cup and we’ve got our stirring implements, the next thing to keep an eye on is how you’re mixing. If you mix too fast it can whip air into the resin- mixing slow and steady takes patience, but it’s worth it for the end results (just keep an eye on your pot time!). I also find that mixing resin in too large of a cup can cause problems. Choose your cup size based on how much resin you’ll be mixing and aim to not just have a thin layer on the bottom, otherwise it gets super bubbly even with slow mixing. I like to have a range of cup sizes from shot glass up to large drinking cup so that I can choose the right one for the project at hand.

Removing bubbles from resin

So you’ve done all you can to avoid adding bubbles but they’re still being a nuisance (or maybe you’re a perfectionist like me)? Luckily there are several different things we can do to either remove bubbles or make it so they’re no longer visible. We’ll start with the cheaper and safer options before discussing what professional resin casters use. You can also combine some of these methods together to get better results.

Option 1- Using a lower viscosity and/or slower setting resin

Resins have a large variety of properties, but the two that are important when considering bubbles are the viscosity of the resin and the cure time. These two things will dictate how well bubbles are able to rise out of the resin before it cures and they’re trapped inside. A high viscosity resin is a resin that is very thick (i.e. more like the consistency of honey than water). These resins can be useful for things like suspending glitter as it won’t sink so fast, but they have the downside of also trapping bubbles much more than a low viscosity resin will. If you don’t need the positive traits of these resins for your project it can be a good idea to instead use a low viscosity resin to reduce the amount of bubbles that will be trapped.

Viscosity will affect how difficult it is for bubbles to rise to the surface, but the other important factor to consider is how much time bubbles will have to rise to the surface. Resins that are both slow setting and low viscosity are ideal for lowering the amount of bubbles in the final cast. They will often be referred to as having ‘self-degassing’ properties as they are able to remove air without the use of other equipment. Other keywords to look out for to find resins with these properties are ‘casting resin’, ‘slow set resin’ or ‘deep pour resin’. To make sure you’ve found the right thing, check that the cure time is somewhere around 48-72 hours. If available, the TDS should also show you what the viscosity of the resin is.

Another option is to lower the viscosity of whatever resin you already have using heat, but this will speed up the cure time so you may have to work quicker than usual. The standard way to do this is to place your closed resin bottle into warm water for a bit before starting. Some people like to place the bottle into a plastic bag first to keep the water off it, but otherwise as long as you don’t submerge the lid you can just dry the bottle off before starting (make sure to do this as you don’t want water accidentally getting into your resin when you pour it). Personally I like to put my resin bottle into a yogurt maker with warm water. It’s vacuum sealed on the sides to keep the warmth in and just so happens to be the right size and shape for my bottle. Any container will do though, but it’s best to use something that won’t ever be used for food again in case there’s any resin residue on the outside of your bottle.

Option 2- Using a heat gun or torch for surface bubbles

One of the problems with bubbles in resin is that you can often get them to rise to the top but then they just sit on the surface and don’t pop. A good way to force them to pop is to use a heat gun, lighter, or a propane/butane torch run lightly above the surface. Using a torch or lighter is superior to a heat gun as the CO2 from the flame causes the bubbles to pop. This works great for large pours such as river tables or coating artwork where the use of a pressure pot or vacuum chamber may not be feasible. You do have to be careful not to use this on any flammable resins (e.g. polyester) or if you’ve added anything flammable to your resin (e.g. alcohol ink). Also, for any mould based work I strongly advise against using these. It’s super common to see people complaining of ruined moulds from their resin sticking to it and it always comes down to them using either a heat gun or torch. It’s very easy to accidentally overheat your resin and cause it to fuse to the silicone. If your resin isn’t too moisture sensitive, an alternative is to use the CO2 from your breath. If you aren’t using a respirator you can use a straw to direct your breath, otherwise positioning your cup under the exhaust part of your respirator and breathing out strongly can also work. It’s best to give your resin a slight mix after doing this to avoid amine blush from the moisture. Another alternative is to pop larger surface bubbles with a toothpick or pin, wiping it between each attempt to keep it pointy enough.

Option 3- Ultrasonic jewellery cleaner

The next option costs a little bit of money, but is generally pretty affordable. Ultrasonic jewellery cleaners use a piezoelectric plate to agitate water in the chamber above. Usually you would place an object into the water and it wears away any surface contaminants, but instead we’re gonna place a cup of resin inside and use it to force bubbles out. You simply place your mixed resin cup into the top and fill water in to the rest of the chamber until it’s as high as the resin is, but not too close to the top of the cup (water and resin don’t mix!). You then turn on the machine and the piezoelectric waves force bubbles to rise up out of the resin. I find it also removes some of the dissolved air which is pretty cool, but this method is limited by the size of the chamber so is generally only good for small to medium projects. You do have to be careful if you’re using a faster setting resin as this will speed up the cure time too. Ultrasonic jewellery cleaners range in price quite a lot, I just have a cheapish one and it works fine. If you keep an eye out you can sometimes get them second-hand pretty cheap too.

Option 4- Vacuum chamber

Going further up the cost scale, the next option is to use a vacuum chamber. Vacuum chambers for resin generally consist of a pot with an acrylic lid connected to a vacuum pump. They work by sucking out all of the air in the chamber around the cup, and once that’s gone it then starts to force out all of the air in the resin too. They’re also good for removing air from bubbly inclusions as it will pull the air out and replace it with resin. I’ve only used mine with my thin casting resin which it works great on, but it might be more difficult to use it on a thicker or fast setting resin as when I tried it with my silicone (which had a much higher viscosity) it took longer to get all of the bubbles out. Vacuum chambers are a relatively safe piece of equipment as long as you haven’t cut too many corners, as in the unlikely event of catastrophic failure they would implode rather than explode. There are lots of guides for making one yourself if you have the tools and space to do that, or you can also buy them ready made.

Option 5- Pressure pot

The last major option is to cure your pieces in a pressure pot. This is what professional casters generally use as it can basically guarantee you a bubble free cast. A pressure pot is essentially the opposite of a vacuum chamber- instead of taking all of the air out, it forces air into the pot resulting in a high pressure within it. This pressure causes the bubbles to shrink so small that they can no longer be seen by the human eye, making casts appear to be bubble free. Pressure pots for resin casting are made by modifying paint pressure pots so you’ll generally need some technical understanding, though there are a lot of good tutorials out there to help walk you through the process. There are a few that you can buy already modified but these aren’t available in every country and will generally be quite a bit more expensive. They also require a compressor to work as this is what puts the pressurized air into the pot. Note that a pressure cooker isn’t the same thing- they work by steam and can’t safely operate to a high enough psi to be useful for resin.

Pressure pots are the most dangerous option on this list, as in a worst case scenario they explode, but as long as you’re not trying to fill it past the pressure it’s designed to handle it will generally be pretty safe. They have safety release valves which prevent the pot from going past the safe operating psi, and many people add 2 of these in case one fails, so they can be a great tool as long as you’re smart about it. The use of a pressure pot generally means you won’t have to worry about using any of the other techniques or equipment in this list as the pot will take care of it, though warming the resin beforehand can still be useful as it makes it easier to mix. The main limitation to a pressure pot is the size, they aren’t useful for every circumstance as large projects such as river tables will obviously not fit inside.

Final useful tidbits & troubleshooting

-Vibration can work similarly to an ultrasonic jewellery cleaner as it helps bubbles rise to the top. Some suggestions I’ve seen for this include placing your moulds on top of a washing machine while it’s in the spin cycle, using a vibration table, or anything else you have around the home such as an old electric toothbrush or back massager
-If you get very large bubbles that definitely weren’t there when you put the resin into your mould, it’s most likely from your resin overheating and boiling. Make sure to not pour past the recommended pour depth of your resin, and instead pour in several layers if your mould is too large.
-Small bubbles stuck to the surface of inclusions or your moulds can be coaxed out with a toothpick. It’s also a good idea to coat inclusions in resin before placing them in the mould to help cut down on bubbles
-If you’re having trouble with bubbles forming on the surface of your silicone moulds that weren’t there when you first poured the resin in, it’s most likely due to moulds that have been made with low grade silicone. You can generally tell if this is the case as they’re often more opaque than other ‘clear’ silicone moulds, more likely to have a bunch of surface imperfections, and may have a strange smell to them
-If your resin completely foams up with bubbles for no apparent reason, it’s most likely that your resin is moisture sensitive and you’ve added a colourant or inclusion that has water in it. Lots of dyes or paints are water based so it’s best to check what the base is made from before using it with resin. Some safe things to use instead include alcohol inks, resin dyes, mica or other powdered colourants

If you have any other suggestions or need any help, feel free to leave a comment down below