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?

Overwhelmed with everything there is to know about resin?  I get it.  I felt the same way when I started creating with resin over a decade ago.  It’s why I wrote the book, Resin Fundamentals.  I share the important details you need to know to give you a clear path on how to make something with resin that will have people saying, ‘Wow, you made that?!’

Unpublished Blog Posts of Resin Obsession, LLC © 2020 Resin Obsession, LLC

Like this post? You may be interested in  How to dry flowers with silica gel beads

17 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.

  5. Can “lakes” of epoxy be poured into large tabletop centers, or is the risk of the wood holding the dimensions firm while the epoxy contracts a legitimate risk? I only see rivers…. in photos, anyway. Are rivers always used to allow the epoxy to move on its own?

    If this is not a clear question just let me know

  6. I’m trying to do a river table with live edge and this will be my first. I’ve read online so many different deep pour articles but I’m getting mixed info and would love some clarification for simplicity sake. The “River” will be about 2″ thick, what resin/epoxy do I need so I can pour ONCE and not many different layers that take lots of time?

    1. Hi Seth, for a project like this, the Resin Obsession deep pour resin works great. You can pour it up to two inches thick in one pour. You can buy it in several sizes in our store here:

      Be sure though, to follow the tips in this article to make sure your resin doesn’t get too hot and crack. Since this is your first time making a project like this, you may want to try a smaller test piece to see how it works.

  7. You all provide excellent advice and ideas. I have an issue I don’t see covered.

    I poured a deep resin table. I poured 8 coats to hit two inches thick. There is about 1/2” of resin over the top.

    The final coat is still just a little tacky. No pockets of resin, but the entire surface is sticky.

    My question is what is the best way to sand it smooth while not marring the surface?

    I’m looking for help!


  8. I have a question .im sorry for my ignorance in advance. Do you go to a table top epoxy after you do ur deep pourepoxy

    1. Hi Tracy, what are you trying to make? The deep pour resin is meant to fill vessels and molds while a table top epoxy is meant to coat surfaces.

  9. I have this same question. I’m making a live edge river bar top that will be outdoors. I understand the risk but since it’s for my own house, I’m willing to take the chance. I have purchased a deep pour epoxy for the river portion and will be using Total Boat Halycon Clear varnish for the final top coat as added protection from UV and water exposure. My question is, can I use the deep pour epoxy for top coat as well, and as a pre-coat on my live edges? Or do I have to purchase a separate table top epoxy for this?

Leave a Reply

Your email address will not be published. Required fields are marked *