Fully cured epoxy resin is completely waterproof, it's true. However, if moisture gets mixed in while epoxy resin is still in its liquid state, it can interfere with the curing process and cause several issues:
The most common ways that moisture can contaminate resin include:
Let's take a look at the effects of moisture on epoxy resin, one by one:
If water contaminates the resin or hardener through wet tools or a water bath, the resin will take on a milky, cloudy appearance. This is why water based paints, like acrylic, aren't the best for tinting resin. Very fluid craft acrylics can make resin turn thick, clumpy and milky because they have such a high water content.
Here are a few examples demonstrating how water can affect a resin cure. The resin is all from the same batch of ArtResin, but contaminated with varying amounts of water.
Clockwise from left:
1. No water: A few microbubbles from pouring so thick, but otherwise properly cured and clear.
2. Water flicked over the resin with a wet paint brush: bubbles, divots and hazy areas.
3. Water dropped into the resin with a dropper: deep channels, trapped water leaking out and soft resin.
4. Water mixed into the resin: a milky appearance from thousands of bubbles, an uneven pockmarked surface, and significantly more bendy than the other samples.
To prevent water from contaminating the resin mixture, take the following precautions:
No, epoxy resin should not be applied over a wet surface. Whether it's a wet painting, wet wood, or paper still wet from the use of sealant or glue, applying resin over a wet surface can result in poor adhesion, bubbles, and an uneven cure.
The following two samples used ArtResin from the same batch over wood coasters painted with black acrylic paint. The paint in the sample on the left was not fully dry and the resin cured with noticeable waves and ripples. In contrast, the paint in the sample on the right was allowed to dry completely and the resin cured perfectly.
For the best results, the surface should be completely dry before applying resin:
Yes, fresh flowers look beautiful in resin, however, they must be thoroughly dry first. If they contain any type of moisture, it can cause the resin to cure cloudy, and the flowers will eventually rot under the resin.
In the sample below, fresh leaves and flowers were embedded in resin without being properly dried. The moisture they've released into the resin has created bubbles, a rippled effect, and a hazy cure throughout.
Dry leaves, flowers and other objects that may contain moisture in silica gel as per the label instructions. Natural objects that may contain trapped air should also be sealed to prevent the air releasing into the resin as bubbles.
Summer temperatures are often accompanied by high humidity. Humidity refers to the moisture content in the air, and it can have an impact on the curing process and appearance of the resin. When moisture is introduced into the mixture, you may end up with amine blush, characterized by an oily film or a cloudy appearance on the surface.
The two samples below used ArtResin from the same batch. The first was allowed to cure indoors, in a climate controlled (air conditioned) environment of about 78F/25C. It cured perfectly clear, as expected, with no surface imperfections. The surface is hard, dry and smooth.
The second sample cured outdoors, covered, but with rain on and off during the 24 hour cure. The temperature ranged from 75-86F/24-30C with humidity levels outdoors ranging from 86-100%. The resin cured with noticeable ripples and waves throughout and developed amine blush - the resin feels tacky and waxy, with quite a bit of resistance as you run your finger along the cured surface.
To achieve optimal results, maintain a consistent temperature and humidity levels below 80%, and preferably at 50%. Using air conditioning can help reduce humidity, and if you live in a highly humid climate, running a dehumidifier the day before resin work can be beneficial.
By controlling humidity levels and minimizing moisture exposure when measuring mixing, pouring, spreading and curing, you can help ensure a successful resin outcome with improved clarity and quality.
We hope these results emphasize how moisture can prevent a perfect resin pour. For the best possible results, work in a dry environment (ideally 50% humidity but anything less than 80% is fine) and ensure that the resin and surrounding materials are free from moisture during mixing, application, and curing.