General resin troubleshooting tips
Originally published November 2013. Updated August 2018.
When working with resin, technique is very important to ensure outstanding results. Here are a few of the commonly encountered problems with using resin and suggestions for how to fix it.
Resin not cured or has not fully cured
1. Resin not mixed in the correct ratio of resin to hardener. Recheck instructions and measure both parts separately and accurately in graduated mixing cups.
2. Resin and hardener not mixed thoroughly. While mixing, it is important to scrape the sides of mixing cups and stirring utensils during the process to make sure the mixture is well blended.
3. Non compatible resin and hardener used together. Use the resin and hardener that came together in the same kit. Using one brand’s hardener with another brand’s resin may keep the mixture from curing.
4. Hardener not added to resin. In order for the resin to cure, a hardener must be added.
5. Not enough time given for curing. All resins have different cure times, from minutes to hours to days. Check to be sure you are giving the resin enough time to cure.
6. Resin is not warm enough or the room in which the resin is being mixed is not warm enough. The resin and hardener, along with the room temperature, needs to be about 70 to 75 degrees Fahrenheit. Warm the resin in a warm water bath in 5 minute increments if the resin bottles feel cool to the touch.
7. Resin or hardener is past its shelf life.
8. Resin is poured in a thin layer. Thin castings taker longer to cure because the amount of heat produced is spread over a thinner area.
9. Too much moisture in the resin casting. Use colorants designed for coloring resin and use resin kits within their specified shelf life times. Also be sure all mixing containers and utensils are dry.
Pot life of the resin is shorter than expected
1. Improper resin to hardener ratio. Do not use more hardener or less resin than recommended. Having more catalyst than what is needed will cause the reaction to heat up quickly and cure faster than normal.
2. Resin and/or hardener are too warm. When the casting environment is warmer than 75 degrees, pot time is shortened. This also happens if the resin and/or hardener are warmed up too much in a water bath before use.
3. The amount of resin and hardener mixed at one time is too large. The resin curing reaction is mass dependent; the more of each item, the more heat produced, the faster the mixture heats up and the faster curing takes place. Do not mix more than the maximum recommended mixing amount from the manufacturer.
Pot life of the resin is longer than expected
1. Improper resin to hardener ratio. Use the exact amount of hardener recommended in order to start the chemical reaction which produces the heat to cause curing.
2. The resin, hardener or the room is too cold. Be sure the room temperature is between 70 and 75 degrees Fahrenheit and the components are warm.
3. The volume of resin and hardener being mixed is too small. Resins require a certain amount to be mixed in order for the curing reaction to occur. Be sure to mix the minimum recommended amount by the manufacturer.
Cured resin has bubbles in it
1. Be careful when mixing the resin. The best way to make sure bubbles aren’t in your final casting is to avoid creating them when mixing the resin. Carefully and deliberately stir the resin and hardener when mixing, but do not whip or whisk it.
2. The resin has reacted to something included in it or the inclusion released bubbles after being added to the resin. Make sure all inclusions are sealed with glue or clear tape before including in resin.
3. Remove bubbles before allowing the casting to cure. Draw them out with a toothpick or use a heat gun to get bubbles to the surface.
Here are some additional tips:
Resin is cured, but surface is tacky
1. Resin and hardener were not mixed thoroughly enough. Be sure to mix completely, scraping the sides of the container and stir utensil several times while mixing.
2. When using polyester resin, this is a normal occurrence. The surface exposed to air during curing will remain tacky, even after the resin has fully cured. Either seal the side with a sealer spray or sand off the tacky surface.
3. Excess humidity when casting polyurethane resins. Run a room dehumidifier during the next casting.
4. Using the last bit of resin stuck to the side of your mixing cup when it wasn’t mixed thoroughly. When mixing the next batch, blend for one to two minutes in a mixing cup, then transfer to a new cup to mix for another one to two minutes.
Resin embedments have ‘wet stains’
1. Seal before including in resin. Any item that can take up water needs to be sealed before using in resin.
Resin and/or hardener has yellowed
1. Resin kit is past its expiration date.
2. Resin kit has been improperly stored. Resin and hardener need to be stored in a cool, dry place, away from sunlight and temperature swings.
3. Resin was opened and used, but stored with a large, open space in the top of the bottle. Exposure to air will cause resin to oxidize and turn yellow. Purchase smaller quantities of resin that you can comfortably use within half the expected shelf life.
If this has happened to you, learn more on what to do with yellowing resin.
Resin has cured cloudy
1. Resin kit contaminated with water.
2. Resin components are cold. Warm the bottles in a warm water bath before using.
What other experiences do you have with resin not curing properly?
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