How to use Craft Resin on a thicker project

Craft Resin self-levels at approximately 1/4 inch ("), which is enough to give a gorgeous glossy coating... but sometimes you may want a REALLY thick coat for certain pieces.


Here's how:


Layer Craft Resin in multiple coats, as high as you'd like as long as you pour in 1/4" increments.

You have two choices when pouring multiple layers:


The first is to pour your first layer, torch out the bubbles, cover and wait 3-5 hours until your resin reaches a jelly like stage. At this point you can pour on your next 1/4" layer, torch out bubbles, cover, wait 3-5 hrs and repeat until you reach the height you desire. This method is especially handy when pouring into a mold or a dam.


The second option is to allow your first layer to fully dry, then give the overall piece a light sanding and pour on your next 1/4" layer. Torch out bubbles, cover and let this layer dry. Repeat these steps as many times as you'd like.


Keep in mind that our recommendation of a 72hr cure time is based on a 1/4" layer. The thicker your layers are the longer the cure time will be. It could take up to 10 days for a full cure, depending on how many layers you've poured.


Tip - Using A Warm Water Bath

Warming your unopened Craft Resin bottles, both A and B, in a warm water bath will alter its viscosity, making it thinner and greatly decreasing the bubbles - this can be a great advantage when pouring into silicone molds and allows you to pour a little bit thicker than our recommended pour of 1/4".



How to control the exothermic reaction for a deeper pour:


Once you combine the resin and hardener, a chemical reaction starts to happen that is the beginning of the curing process. As with many chemical reactions heat is a normal byproduct of this. Heat output is greater with the larger quantities of resin that you use.



When mixing larger batches of resin and hardener, pot life, or the amount of time that elapses before the epoxy hardens in the container is very important. You need to estimate how much mixed epoxy you will use in a certain amount of time. Variables that affect this calculation include temperature, volume, surface area.


For every 18°F increase in temperature, pot life is cut in half. To increase the pot life of a cup of mixed epoxy, spread it over a larger surface area, work in a cooler environment, or mix multiple, smaller batches as you go.


The chemical reaction between resin and hardener as epoxy cures will generate heat. When this heat cannot escape, it builds up, causing the epoxy to cure faster because epoxy cures faster at higher temperatures. Curing faster because of the heat, the epoxy generates even more heat, even faster. This snowball effect is why a gallon of epoxy mixed all at once will turn solid in about 5 minutes. The resulting massive build up of heat can cause the cured epoxy to crack because of the temperature differential between the top and bottom of the container.

This uncontrolled heat build-up is called uncontrolled exotherm. Epoxy heating out of control can foam, smoke, give off dangerous vapours and generate enough heat to melt its container or cause nearby items to catch fire. It’s crucial to understand epoxy’s exothermic curing reaction.


The mechanism that causes heat buildup when epoxy is contained in a thick mass is also why epoxy takes longer to cure when it is applied as a thin film. The film does not build heat, so the temperature through the thickness of the epoxy film is pretty close to the ambient temperature.

Occasionally customers are interested in filling a void by pouring a pouring large mass of epoxy all at once. This can be very dangerous because it will generate a lot of heat, and can lead to poor results because of the snowball effect mentioned earlier.


Pouring a large mass of epoxy is a very difficult to do safely and effectively. Temperature, volume of epoxy, depth of the epoxy, and amount of heat sink in contact with the epoxy are all major variables in this application.


Proven methods for controlling exotherm:

If you do want to pour or cast a large volume of epoxy, here are several proven methods for minimising heat buildup which we’ve developed over the years.


Pour the epoxy in timed, multiple batches.

Timing is important when doing multiple pours. Ideally, you want to wait for mild exotherm to peak and begin falling before mixing a new batch and pouring. Waiting too long could cause an insufficient bond between the two pours. Not waiting long enough can cause too much heat to build and cracks to propagate.


Work at cooler temperatures.

Cooler shop temperatures and cooling the epoxy itself will both work to your advantage in slowing cure and controlling epoxy’s exothermic reaction. A deeper pour can be accomplished with less heat buildup by starting with cooled epoxy and a cool substrate until the epoxy initially cures to a soft solid. Then you could expose it to room temp or higher to complete the cure.



The tips in this blog are specific to Craft Resin, if you are using another brands resin please check out their guidance before you begin.


If you have any tips of your own to help our readers, please pop them in the comments below.

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