Deep pour resin casting tips – resin river table advice

deep pour resin casting tipsWhen it comes to using resin, there is a cardinal rule you have to follow whether you like it or not.

The resin always wins.

What I mean by that is resin will do what it’s supposed to do. We, as crafters and artists, need to work within the confines and the limits of the resin to get the results we want.

How do you do that?

Let’s start with resin chemistry

Okay, I’m not going to go all high school chemistry on you but, there are a few basic things you need to know.

The part A resin is an epoxy, built of long chains of molecules that contain several elements. The side B hardener is an amine-based chemical, which is specially formulated to link with the part A epoxy. (That’s why using one manufacturer’s resin with another manufacturer’s hardener can be a reason why your resin doesn’t cure.)

By themselves, the resin and hardener don’t do much, but the magic happens when you combine the two. The parts of each merge to start a chemical reaction, which crosslinks all the molecules.  This crosslinking produces heat and eventually creates a solid mass of resin.  Feeling your resin get hot is a good thing. This is what we see as the resin curing!

One of the great things about using a deep pour slow curing epoxy resin is that it creates heat slowly. The advantage of a resin like this is that you can pour thick layers of resin at once.

But this can create another problem

The thicker and larger the area of resin poured, the hotter the mixture gets.  As more crosslinking occurs, more heat is produced, adding to the heat of the mass of resin.  A larger, thicker mass of resin is going to get hotter and take longer to cool than a thinner, smaller mass of resin.

So why does this matter?  As the resin and hardener mixture heats, then cools, the combination shrinks to accommodate the newly-organized molecule chains of the resin and hardener mix. The shrinkage is directed to the center of the resin pour.  While a little bit of shrinkage is to be expected when casting with resin, excess heat can lead to a lot of shrinkage.  When the center of the pour can no longer absorb the shrink, a crack develops.

What does this ultimately mean?

The thicker the pour of resin, the more care that needs to be taken to get rid of the heat, even in resins designed for deep pours. While the specific instructions for deep pour epoxy resin are a great start, unfortunately, they can’t explain or anticipate what could happen in every situation.

So what should you do?

Here are my best deep pour resin casting tips:

*Pour in layers, letting the previous layer completely cool before pouring the next layer.  The heat of layers is additive, meaning any heat from the first layer will add to the heat of the reaction to the next layer.  By letting the previous layer fully cure before pouring the next layer, you will see a line between layers when looking at the side, but it will be less likely that you will see a crack when looking through the top of your project.

*Your mold box can contribute to heat retention. Mold boxes made from wood will retain heat and make overheating and cracking more likely to occur.  Mold boxes made with thick lumber planks are easy to make but are also excellent heat insulators.  Better mold material choices include melamine board, polypropylene and HDPE plastics, aluminum and medium density fiberboard coated with Tyvek plastic.

*Look for other ways to get rid of extra heat. Elevate the mold box off your casting surface, then use a fan to generate airflow underneath and around it. You also want to be sure your casting room is not too warm. The low 70’s F is ideal.

*Be careful not to overheat your resin. Warming resin before casting is a great way to thin the components, making it less likely you introduce bubbles into the mixture. This warmth, though, adds to the heat of the reaction. Warming up your resin for too long can cause reaction overheating. If you don’t believe me, you can see what happened when I overheated resin.

What other deep pour resin casting tips do you have to share?


Unpublished Blog Posts of Resin Obsession, LLC © 2020 Resin Obsession, LLC

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8 thoughts on “Deep pour resin casting tips – resin river table advice

  1. Not a new tip about curing but from a newbie like myself it is a hard-learned tip.
    When mixing the hardener + epoxy stir until the cloudy mix turns almost clear.
    If you don’t do that you’ll get a permanently sticky mess.
    If you do that it’ll cure nicely.

  2. When I pour resin into my wood projects for turning I always pre-coat the sides first which helps prevent air bubbles.

  3. I am new to resin pouring and have an irregular shaped end live edge piece of cherry that has some large cracks in the end. I don’t want to straighten/cut the end off but curious how to build a mold or box to accommodate the end so the resin doesn’t just run out…ideas?

  4. Had a similar situation myself. It’s pretty common.
    Build the frame around the piece or at least the ends that have the cracks.
    Get some tuck tape, attach it to straight pieces of plywood, and attach that to the project piece.
    Attach additional tuck tape to any exposed cracks on the sides or underneath the project piece where resin might want to leak out from.
    Then pour.
    But be careful not to over pour. You might want to cover the area around the crack(s) you’re filling.
    Unless you’ll be planing or sanding the whole thing off afterwards.
    Removing resin through sanding or with a card scraper is easier than I thought it would be but if you’re using pigment it can get through the wood fibers around the filled crack where you don’t want to see discoloration.
    And don’t forget to thoroughly mix the resin to avoid a sticky mess.

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