It is not just about gloss and shine. If you are using epoxy resin to coat your products, then it is important that the surface remains colorfast.
Epoxy resins can yellow over time due to exposure to air or sunlight, which makes them look less than perfect. So what can be done? There are a few steps that should be taken in order to prevent this from happening.
Table of Contents
Does All Epoxy Resin Yellow Over Time
Epoxy resin is made up of a chemical called Bisphenol-A. It’s this compound that makes it possible to have epoxy resins in many different colors, but also responsible for the yellowing that eventually happens over time.
The oxidation process can be slowed down by using additives like UV light blockers or antioxidants, however these are often not included in DIY kits.
How Do You Fix Yellow Resin
If you have a yellow resin that is already dry, then there’s nothing you can do to fix it. But if the epoxy glue has not yet dried and your goal is to prevent it from going bad due to oxidation or being exposed to air through evaporation, here are some tips:
Smaller containers will speed up cure time but also decrease exposure times, so keep an eye on them closely as they may start curing faster than expected.
This would be ideal for small-scale projects where quick turnaround isn’t necessary; however, drying out of the container before use could still occur at such high temperatures (and thus shorter working windows).
Store in a cool area with low humidity levels like inside a cabinet or basement.
Mix in a small number of additives like Vinylester or Polyester Resin.
This will increase the cure time and decrease yellowing, but it is only effective when used with epoxy (not polyurethane).
What Epoxy Does Not Turn Yellow
The key to preventing epoxy resin from yellowing is to use the right type of hardener.
The three types are slow, medium, and fast curing hardeners. Fast curing resins turn white or clear in just one day while slow cure takes nearly six days.
Medium-curing resins fall somewhere in between the two extremes with a four-day window for full hardness during which time it can be handled without damaging its strength.
Why Is My Clear Resin Yellow
As mentioned in the introduction, yellowing is an effect that occurs when exposed to light.
This process can also be accelerated by heat or humidity which will speed up chemical reactions between molecules in your epoxy resin.
The most common reason for a clear epoxy substrate turning yellow is impurities within the resin formulation itself.
Impurities typically come from solvent evaporation over time and exposure to UV lights during curing of product.
Other reasons why you may see your clear material change colors include:
oxidation (yellow/brown) due to water damage, long-term storage conditions such as extreme temperatures both hot and cold, or excessively humid areas where mold growth can occur on surfaces not properly protected with packaging materials such as bags and boxes, etc…
How Long Does It Take For Epoxy To Yellow
It’s difficult to give a definitive answer because each situation is different, but it usually takes months or years for epoxy resin to start yellowing.
This time frame will depend on the type of UV exposure and also what kind of materials were used in the initial application.
Why Is My Epoxy Hardener Yellow
Epoxy hardener is not always white it can be yellow, orange, or red. This means that your epoxy has gone bad and should be discarded.
If you see this color discard the product immediately because it will cause a poor long term bond between two materials.
Does Stonecoat Epoxy Yellow
Stonecoat epoxy can be yellow if not applied correctly or dried for too long before sealing. To prevent this, always follow the manufacturer’s instructions and work in a well-ventilated area with low humidity.
What Is The Difference Between Resin And Epoxy Resin
Epoxy resin is a type of plastic that can be turned into an adhesive, hardener, protective coating, or filler.
There are many different types of epoxy resins including:
General purpose (clear)
UV curing (ultraviolet light activated polymerization)
Bisphenol A (chemical name for the base monomer), melamine-formaldehyde
Epichlorohydrin/glycidyl ethers-Ethylene oxide gas cureTwo part systems generally use bisphenol A as its base monomer because it has higher cross linking density than other types and therefore stronger adhesion to various surfaces.
How Do You Whiten Yellow Resin
There are a variety of ways to whiten yellow resin. Here’s how:
Mix in some white pigment or filler powder with your resin while it’s still liquid and stir well before pouring the mixed epoxy into your mold.
This will help lighten its color by covering up any yellowness, but you’ll have less material to use for casting since you’re adding more powder than usual.
You should also expect that this method will slightly reduce the strength of cured castings since there is an additional volume being added during mixing process which weakens the final structure.
And finally, if you add too much coloring agent to try to get rid of all signs of yellowing, then your cast part may end up looking a bit chalky instead.
The next option is the easiest and most efficient method of getting rid of epoxy’s yellowing, but it has its drawbacks too:
mix a little clear filler powder into your resin before you pour. What this will do is allow any yellowness to be dissolved by the liquid portion of your mixture so that there are no coloration differences between batches.
However, since more material (more than usual) is needed for mixing in with each batch in order to make up for what gets washed away during use, this can result in having less original material left over when casting if you don’t want to waste it all on trying out different mixtures.
Plus, depending on much pigment or filler was used for this process, your parts may end up being a bit cloudy or opaque instead.
The last option for removing yellowing from epoxy resin is the most effective but also requires more work and equipment: use an ultrasonic cleaner.
Mix in some white pigment with clear resin before pouring it into the machine’s tank so that you have enough to cover any yellowness which will result after going through the cleaning cycle as well as adding a little extra just in case there was too much excess mixture used during the whitening process.
Afterward, let everything sit overnight inside of the U-shaped plastic container shield at room temperature until all bubbles are gone from within each part before then slowly heating them up to around 80°C (176°F) by gradually increasing the temperature over a period of about an hour or so.
This part is important since overheating can cause yellowing to come back, especially with epoxy resins that contain styrene, potentially turning your parts opaque again instead of remaining clear after cleaning and whitening them!
Afterward, let everything cool back down before removing all cured castings from inside the ultrasonic cleaner’s tank.