Reducing Bubbles in Resin
Updated: Oct 18, 2022
Preventing bubbles in resin is a common question amongst resin crafters. First of all, bubbles are a very common thing.
There are so many things that can cause it, and sadly it's not always obvious what did cause it. Trying to learn the ways to avoid creating them, might not be as quick and easy as we'd like, but they are the best way to reduce bubble issues occurring in cured pieces. Once people have it figured out, they produce beautiful results more regularly. Note that even pros with 10 plus years experience have set backs now and then. All resins do behave a bit differently than each other. If you're used to doing things a certain way with one resin, you may need to change the processes a bit for best results, when switching to another type.
When you are creating resin art on panels or flat surfaces, the bubbles can easily be torched out, however when you are creating casting in moulds, it's not the same. Torching can fuse your mould to your resin, ruining both the casting and the mould. Never let flame from a torch touch your silicone mould. A barbecue lighter that you keep away from the resin and mould, and not allow flame to touch could be okay to assist in bubble reduction. But many people use a very fine mist of 99% alcohol to help pop any surface bubbles. You can also use a pipette or syringe to suck up some bubbles. Ideally though, when working in moulds, it's best to reduce potential for added bubbles well ahead of pouring in to your moulds.
Organics and pour out materials ( flowers, wood, leaves, fabric and even paper), can easily add bubbles to your piece. When you cover these materials with resin, the air bubbles release into the resin in the form of bubbles, sometimes hours after you have poured and torched. All bubbles may not be controllable, however there are some tips that can greatly help reduce them.
More common causes of added bubbles are:
. Mixing too quickly.
. Cold resin, room or items used in process including substrate or moulds.
. Resin is reacting to something added to it, sprayed on it or possible contaminant in or under it.
. Bubbles often release off of items when adding an inclusion in to a resin casting.
Here are some areas to consider for reduced issues with bubbles:
1. Temperature is a huge factor with epoxy resins. You will always have best results in a consistently warmer/ambient room (from start though to cure).
There is always certain times of the year, that people who never had a problem before, all of a sudden have a problem. And more often than not, it is interesting when we check for weather changes in their location, that is often what we see (even when a person states they keep their space at a certain temp, it is possible for humidity changes to effect resin as well). A warm temperature is best for resin castings. Regular resin art works well in temperatures of 21C to 26C (70F to 77F) degrees, and room temp needs to be consistently warm throughout curing process.
Our colder climate weather (in Canada) poses challenges for keeping rooms ambient for resin projects. Thanks to a recommendation from a 10 plus year resin artist, I bought a heating unit that works great in my application. The unit recommended is ideal for not blowing air into the space, and it self regulates the temperature. I have in-floor heat that keeps my basement space warm in the winter, however in the summer & warmer days, my basement studio has the in-floor heat off, so I require a space heater to keep it warm during the entire process, through to cure. I added the type of heater recommended to me at the bottom of the blog.
Occasionally people suggest using a heat type mat if working in a cold area. Some people have made set-ups for keeping their projects warm during cure. Ideas like using a plastic tub with a heating blanket underneath are not ideal, as it holds in the heat and can prematurely age the resin. We’ve seen well-meaning people getting creative putting heat lamps, space heaters, etc too close to their cups or other epoxy resin projects, trying to get them to dry faster. Keep in mind, sure, this will speed up the drying process... Not the curing.... but the drying. But these more direct heat methods could also cause pre mature yellowing on your projects. Please keep that in mind.
***Important note: Heating the whole room or work space area is great. Direct close contact heat is not ideal, & it is not the same thing.
Tip: Buy & regularly use an infrared thermometer. You can aim it directly down the neck of resin bottles (once lid removed), substrate, mould, etc., to see what the actual temperature is (instead of guessing or assuming). If you start to make notes of the information, you can track what works best for you, in your space (what works best is often different for each person, and remember weather changes can effect the way things are done too).
2. Sometimes people want to use one type of resin for every type of project, but depending on what projects you do, this may not give you the best results possible. A casting resin (we currently carry 4 different ones), is best used for creating projects in moulds. Three of the four casting resins we carry, are thin (like water) viscosity, which helps keep the bubbles to a minimum, and when bubbles are formed, they dissipate easier in the thinner resins. Thicker resins, like iCoat CT Countertop resin or iCoat MV resin, are great for wall art, doming projects, topcoating, and various shallow casting resin art creations, however thicker resins absolutely do have more bubbles. We have customers that do choose to use the top-coating resins (for their faster cure times), occasionally in moulds, but they should only be used for casting in less than 1/4" layers per session, (keeping In mind top-coating resins are meant to be used at about 1/8” depths). These customers have played with it enough to know how to reduce the bubbles ahead of time. The bubbles need to be able to travel up and out, and the thinner viscosities enable that better. Heating bottles of thicker resins ahead of time, can help minimize bubbles. Just be aware that when doing so, it also reduces your work time/pot life for the resin.
3. If your resin is cold to begin with, it will bubble more in mixing (especially thicker topcoating/art resins). Many people find warming up Part A bottle and Part B bottle, can help. Some people use warm/hot water in a sink or bucket to do this. Ensure you thoroughly dry the container off before pouring resin out, as any little moisture drops of water from container, can ruin your resin cure. Some people set their resin containers & mix cups, on a heating blanket, or near a heater to warm it up prior to working with it. The very thin viscosity resins that are already like water, don't often require much heating up (unless super cold), as they will not get any more viscous from heating, then they already are.
***When doing any type of warming up the resin, don't overdo it. When warming up resins, it can shorten your pot life with any viscosities of resin. With thicker resins, you can also cause the chemical reaction to occur too quickly if you've warmed it up too much. Keep in mind, when you warm Part A & B, you will reduce your pot life and speed up the cure process. Even just warming up Part A can still shorten pot life if warmed too much. Ideally use warmer tap water, (apx 15 minutes should work). If it starts to warm up and thicken while still sitting in the mix cup , it is known as premature exotherm. Premature exotherm can cause a variety of extra issues. One issue, is it can cause is unnecessary added yellowing. Another thing it might cause, since it's now almost in mid-cure, is it may not bond correctly. There are others discussed in the main tips blog.
4. We discuss mixing thoroughly, but gently in our instructions. Mix for 4 mintues, or until all the striations are gone, occasionally scraping along the sides and across the bottom. Many people find using non-wood stirring tools creates less bubbles, since wood is porous. Using a plastic or silicone or steel stirring tool is often suggested for less bubbles. When making larger batches, it is harder not to introduce bubbles.
With casting resins, we recommend letting mix cup sit for about 5 minutes after stirring for bubbles to come to the top and dissipate prior to pouring gently into moulds.
However, with the topcoating/art resins being a thicker viscosity, we do NOT recommend letting it sit in mix cups, rather getting it out on to the substrate as soon as possible to get most pot life time out of it. If you leave the topcoating/art type thicker resins sit in the mix cup, you will encourage it to begin the cure process sooner than it should (premature exotherm).
In either case with any viscosity, know ahead that you will need to have a way to get rid of any bubbles once you have finished with your creation(s), before leaving them to cure.
5. Are your surfaces cold, that you are putting your resin into or on? Temperature differences can produce surface tension, which could cause bubbles to get trapped during pouring. If working with moulds that are oven safe, you can gently warm them (at about 150F) before using, or you can slightly warm substrates/tops/moulds/bezels etc with a low setting on a heat gun, or warm hair dryer. Keeping in mind moulds do not like to be overheated, do this very carefully. We have a separate blog about mould care. For most top-coating projects, it is quite easy to pop bubbles that come to surface, but if they're trapped under from the surface tension of substrate being cold, it is trickier to catch them. If the surface resin begins to cure while those bubbles are still underneath, it is too late.
6. In moulds, some people use a dusting of complimentary coloured mica powder to help decrease the surface tension of a mould. Or some use a fine dusting of baby powder, which they say can help reduce the bubbles close to the mould. Keep in mind this effects the resin shine to dull as well. if wanting to use this method, use a soft & delicate paint (or better a makeup) brush to dust the powder in, then tap out any extra (from the mould), before pouring resin. While I have used mica in moulds, I have not personally used the baby powder option, but I have seen recommended by numerous casting artists. If you choose to try this method, practice on smaller pieces first to see if it works for your application. When ever trying anything new, it's best to practice on smaller pieces to get the hang of how it works for how you use your products.
***Another way to break surface tension, is to roll a small amount of resin around your mould/bezel first, before completely filling it. If there are any bubbles showing at that time, it will be easier to pop the bubbles now, because there is less vertical space for them to move around in or get trapped under other resin. And for more intricate moulds, you may need to pick them up and manouver them around several times during pouring resin in.
7. Any additions or inclusions can be another huge source of adding bubbles. They each can also have their own source of additional surface tension, or potential oils from fingers, or other possible contaminants that may get added to a piece. Sometimes the issue comes from contaminated tools. For some inclusions, it can be necessary to dip inclusions in resin prior to adding them into your mould/bezel to help break surface tension on those. Once you have dipped them into resin, put them gently into your mould/bezel on an angle, then carefully slide into place. When putting inclusions flat onto resin surface, you can easily trap bubbles underneath (they may or may not move outward during cure).
8. Once your current resin session is done, depending on item, go over the piece with a heat source to pop remaining bubbles. If it's a casting, you can use either a light fine mist spritz of 99% isopropyl alcohol, or barbecue lighter with adjustable to low flame, using caution. Do not allow flame to touch resin or come near mould. Some artists prefer using an embossing heat gun, or other gentle heat sources. Sometimes heat guns can blow dust or hair in the air into your piece, or the airflow can move your design off. We prefer to recommend the barbecue lighter gentle flame option never allowing flame to touch mould or resin. Another thing to be aware of with the heat gun, is some artists suggest use of a heat can start to cure the resin from the top, so you may be trapping the bubbles within. In castings, and trying to avoid adding heat, you can use a pipette or syringe to suck up bubbles.
If it's a topcoating and larger type piece, use a propane torch with a wider flame thrower, and again, keep the flame from touching the resin or any surface. The butane chef torches can be used, but they tend to throw a pointy direct flame, so using it on a slight angle (if piece is wide enough) may save accidental singeing of resin. These chef torches are not ideal due to the pointy direct flame they typically throw.
The c02 from the flame is what pops the bubbles so there is never a need for flame to touch any resin or surface area. If you overheat it or singe the resin, it creates undesirable results in the cure. Another option I have mentioned if bubbles are at the top or sides of the mould, you can try to push them in to the middle to pop with heat, or heat a sewing needle with a barbecue lighter and try to pop bubble without the needle touching the mould. Or, if it's high viscosity resin, you can use a pipette or syringe and large bore needle to suck up the bubbles carefully.
Some people like to use a light fine misting of 99% isopropyl alcohol to pop bubbles, many resin manufacturers do not recommend this, as it could negatively affect the cure with pinholes or a splotchy finish (so be aware while it may reduce bubbles, it may possibly effect finish). This issue is typically only if someone overdoes the alcohol though. Sometimes overheating/ overtorching can cause wrinkles or crinkles in your finish. Be aware, certain colourants can also be responsible for any added oily residue on cured finishes.
Some people like to set their work on or by a light box (depending on type of mould), to help check for bubbles before leaving piece to cure. Remember not to move your piece however, once the curing process has started.
9. try tapping the Mold sides or vibrating the piece, to help release any bubbles that may be stuck on the sides of the Mold.
iCoat Depth and iCoat TP21 Casting Resin, are very low viscosity so some of the best for the least bubble producing epoxy resins. I love the results they can achieve without having to resort to a pressure pot. However in some cases, an artisan or crafter may choose to use a pressure pot regardless.
Some people will use a pressure pot for certain projects & various resins. The mould and casting are placed into a pot, and pressure is created inside this pot. The pressure makes the bubbles smaller than the eye can see.
Again, numerous casting artisans have found iCoat TP21, to be the answer to avoid a pressure pot, for many years now. It just takes some experience & getting conditions right in each persons space, for optimum results. The iCoat CE4100 HV is a medium viscosity resin that is well liked for floral castings, but the temperatures involved are imperative for nice results. This HV resin must be heated to 82F in the bottles prior to mixing. There is a blog on our website about that.
After much research & chatting with other resin artists, this is the heater I bought at Canadian Tire, for my basement studio space (During 50% off sale). It doesn’t blow air around the room, (so no added movement of debris in the air potentially landing in curing resin work). It regulates the temp to what you set it at, so the room stays at a consistent temperature which is important through curing process.