ThickSet vs. Fathom: Which Deep Pour Epoxy is Right for You?

If you've been going back and forth between ThickSet and Fathom, you're not alone. Both are crystal clear deep pour epoxy systems built for river tables and casting work. The question is which one is right for your project. It really comes down to two things: how deep you need to pour in a single layer, and how much control you have over your workspace temperature.

At a Glance

ThickSet is a cast-and-coat epoxy that builds depth in multiple layers with as little as 4 hours between pours. It pours up to 1/2" per layer for river tables and slabs, and up to 2" for smaller castings. It's more forgiving of temperature swings — a great choice when your shop isn't perfectly climate controlled.

Fathom is designed for deeper single pours — up to 2" for river tables and slabs, up to 3" for smaller castings. It generates very little heat as it cures, which is what makes those depths possible. The tradeoff: it requires precise temperature control and a longer wait between layers or to demold.

Still not sure? Keep reading.

What Is Deep Pour Epoxy?

Standard coating and tabletop epoxies are designed for thin layers — typically 1/8" to 1/4" at a time. Deep pour epoxy is formulated to cure slowly and generate less heat, allowing much thicker single layers without yellowing, cracking, or surface distortion. Both ThickSet and Fathom are deep pour systems. The difference is how deep each can go, and what they ask of you in return.

ThickSet Deep Pour Epoxy Resin light-up shelf

ThickSet Epoxy: Faster Builds, More Flexibility

ThickSet is versatile enough for both coating and casting applications. It pours deeper than a standard tabletop epoxy, gives you enough working time to work out bubbles and position embedded objects, and lets you build depth without sanding between layers.

Pour Depth and Layer Timing

Pour up to 1/2" per layer for river tables and slabs, or up to 2" for smaller castings using 10 fl. oz. or less. Exceed those limits and you risk trapping heat, causing yellowing, surface waves, or cracking. The next layer can go down in as little as 4 hours — no sanding required.

Pro Tip: For the cleanest results, pour your next layer while the previous one is still in its recoat window while it’s tack-free but not fully hardened. Pouring onto a fully cured layer without sanding first can result in a visible line between pours. If your previous layer has gone beyond the recoat window and hardened fully, sand it lightly with 80-120 grit, wipe clean with denatured alcohol, and then pour your next layer.

Mix Ratio and Working Time

ThickSet is 1:1 by volume (equal parts resin and hardener). Pot life is about 10 minutes at 70°F; total working time is 30 minutes. Pour immediately after mixing to get the most out of your working window. ThickSet can be demolded in 24 hours, and reaches full cure in 3-5 days at 65-75°F.

Temperature Requirements

ThickSet performs best between 65-75°F with humidity below 60%. Below 65°F, it becomes too thick to self-level and release bubbles. Above 75°F it sets too fast and can yellow or distort. It's a more forgiving range than Fathom — if your shop temperature fluctuates day to day, ThickSet is the more practical choice.

ThickSet Is a Good Fit If...

• You're building a river table, slab, or bar top in multiple layers
• You want a faster build with shorter waits between pours
• Your workspace temperature isn't perfectly stable for days at a time
• You're doing smaller castings up to 2" deep using 10 fl. oz. or less
• You're newer to deep pour epoxy and want a more forgiving system

Fathom Epoxy: Deeper Single Pours, Fewer Layers

Fathom is engineered for thick, deep single pours. Its extremely slow cure generates very little exothermic heat — that's what allows it to go so much deeper per layer without the problems that would ruin other systems.

Pour Depth and Layer Timing

Pour up to 2" per layer for river tables and slabs, or up to 3" for smaller castings in prepared molds (1 mixed gallon maximum). For many projects, that means a single pour gets you to your final depth. Fathom also has minimums: at least 1/2 gallon of mixed epoxy per pour, and not recommended for depths under 1", as it significantly extends cure time.

When step-pouring, wait a minimum of 36 hours between layers. If you need to move faster, 24 hours is possible — but check the center of the epoxy mass with an infrared thermometer first. It needs to be below 85°F before the next layer goes down.

Mix Ratio and Working Time

Fathom is 2:1 by volume (2 parts resin to 1 part hardener). Working time is 4-6 hours — significantly longer than ThickSet, giving you more runway for complex pours and encapsulations. Let the mixed epoxy rest in the pail for 20-30 minutes before pouring to let bubbles rise. Demold time is 48-72+ hours; full cure is 5-7 days.

Temperature Requirements

The application range is 60-80°F, but for thick pours the optimal target is 70°F. Never use Fathom above 80°F. Its exothermic reaction is delayed — heat typically develops 6-20 hours after mixing, not immediately. That means you need to hold workspace temperature steady through the full cure, not just at pour time.

Pro Tip: For pours up to 1.5" thick, you can raise ambient temperature to 90°F after 20 hours to help speed up the cure once the epoxy is past peak exotherm.

Fathom Is a Good Fit If...

• You're building a thick river table or slab and want to minimize the number of pours
• You need to go deeper than 1" per layer on larger pours
• You have a climate-controlled workspace and can hold temps through the full cure
• You're doing large casting work where depth is the priority
• You have time built into your schedule and aren't in a rush

Exothermic Reaction: What Is It and How to Avoid It

Exothermic heat is the warmth generated as epoxy cures. The larger the mass and the deeper the pour, the more heat builds up — and left unchecked, it causes yellowing, cracking, surface waves, or worse. A mixing cup left beyond its working time can reach 200-300°F.

ThickSet manages exotherm through step-pouring — keeping layers thin enough that heat dissipates before the next pour. Fathom generates very little heat by design, but its reaction is delayed 6-20 hours after mixing. Temperature control has to be maintained well after the pour, not just while you're working.

No matter which epoxy you use, never exceed the recommended pour depth. Only mix what you'll use immediately, and never leave curing epoxy in an enclosed container or near combustibles.

Popular Deep Pour Epoxy Projects

Epoxy River Tables and Live Edge Slabs

For channels under 1", ThickSet is practical and fast — multiple 1/2" layers with 4 hours between them. For a 2"-deep channel where you want it done in one pour and your shop is climate controlled, Fathom is the better call.

Deep Casting and Molds

For thick casting work — sculptures, woodturnings, flower preservation— Fathom's 3" single-pour depth reduces the number of layers and the risk of visible lines. ThickSet can get there in multiple ½-2" layers if you're not working in a climate-controlled space.

Bar Tops, Countertops, and Coating Applications

ThickSet is the better fit here. You don't need Fathom's depth for surface coatings, and ThickSet's faster recoat window makes the build much quicker. Coverage is roughly 3.2 sq. ft. per gallon at 1/2" thickness.

Embedding and Encapsulating

Both work well for embedding objects like bottle caps, coins, and flowers. Fathom's longer working time gives you more runway to tackle bigger pours, detailed dioramas, river tables, and other large-scale projects. Or build your project one layer at a time with ThickSet for greater control over object placement and fine details.

Common Issues and How to Avoid Them

Bubbles

• Temperature too low: Below 65°F, ThickSet won't release air bubbles properly. Warm your workspace and materials before pouring.
• No seal coat on wood: Always seal porous substrates first. Without it, air bleeds out of the grain and gets trapped in the epoxy. A heat gun won't fix this. For ThickSet projects, you can use a thinned coat of ThickSet itself as the seal coat. For Fathom, ThickSet won't work since Fathom cures too slowly to bond properly over it — use TotalBoat High Performance Epoxy instead. Let any seal coat cure fully before your deep pour goes down.
• Overmixing: Stir slowly and let the mixed epoxy rest a few minutes before pouring. For ThickSet castings, a pressure pot at 50 PSIis the most effective bubble solution.

Yellowing or Warping

Almost always caused by exceeding pour depth or working above the recommended temperature range. With Fathom, remember heat builds 6-20 hours after the pour — a workspace that warms up overnight can undo an otherwise perfect pour.

Epoxy Didn't Cure Properly

• Wrong mix ratio: ThickSet is 1:1 by volume; Fathom is 2:1. An off ratio results in a sticky or soft cure.
• Incomplete mixing: This is the most common cause of soft spots. Remember to scrape sides and bottom when mixing, transfer to a second container, and mix again. Never scrape the last drops from the mixing cup into your pour - this helps reduce the risk of accidentally having unmixed epoxy in your final project.
• Temperature too low during cure: For ThickSet, try raising the ambient temperature to 80-90°F for 12-24 hours to help the reaction develop. For Fathom, the same principle applies — warming your workspace to 75-80°F is the first thing to try, and giving it more time is the other option. Keep in mind that cooler conditions or pours smaller than the recommended ½ gallon minimum can extend Fathom's cure time dramatically, so patience is key.

Fisheyes

These uneven low spots in epoxy are caused by contamination in your mold or materials, such as oil, wax, dust, or sap. Clean surfaces thoroughly before pouring. Small fisheyes can be filled with TotalBond CA Glue or TotalBoat UV Cure Clear Resin. Sand with 220-grit before recoating.

Frequently Asked Questions

Can I use ThickSet and Fathom together?

Not in the same pour, but you can absolutely use them in the same project. A common approach is to use ThickSet for an initial layer — great for embedding objects like bottle caps or coins near the base — then pour Fathom on top to achieve the full finished depth. ThickSet and High Performance Epoxy are both good options for a seal coat on porous wood before pouring Fathom. Either way, the same rule applies: let the previous layer cure fully before Fathom goes down.

Can I add color to ThickSet or Fathom?

Yes — both accept mica powders, alcohol inks, universal tints, and pigment dispersions. Mix resin and hardener completely first, then add colorants. Always test a small sample and let it fully cure before your final project.

Is deep pour epoxy UV resistant?

Both ThickSet and Fathom are UV stable and won't yellow from indoor sunlight exposure. However, for projects that will live outdoors or with heavy, prolonged sun exposure, a UV-protective topcoat or varnish adds extra long-term protection.

Still Not Sure Which One to Grab?

If you want speed and flexibility and your shop isn't perfectly climate controlled, go with ThickSet. If you need deep single pours and have a controlled workspace, Fathom is built for it.

Either way, you're working with a crystal clear casting epoxy built to deliver professional results. The right choice is the one that fits your project and your shop!

Have more questions about ThickSet, Fathom, or which deep pour epoxy is right for your project? Our technical support team is happy to help. Reach out at info@totalboat.com or give us a call at (401) 396-8199.