Deep Pour Epoxy Depth Ratings: Why Labels Disagree — and What a River Table Really Costs
Deep Pour Epoxy Depth Ratings: Why Labels Disagree — and What a River Table Really Costs - A step into the workshop.
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There's a moment in every river-table build where the money stops being theoretical. The slab is flat, the mold is taped and waxed, and you're standing over a bucket of mixed resin that cost more than the wood. Pour it right and you've got a dining table. Get the depth wrong and the middle of that pour turns into a furnace: the resin yellows, distorts, cracks, and you get to chisel $400 out of a mold and start over.
So the number on the label matters. Which is a problem, because the labels don't agree. Not even close.
The Label Lottery
Here's the spread, every figure from the manufacturers' own pages and instruction sheets:
- MAS Deep Pour (3:1 mix): half an inch for a full 1.3-gallon kit, 1 inch for a half kit, per MAS's instruction sheet.
- TotalBoat ThickSet: 2 inches, but only for small castings under 10 ounces mixed. For a river or slab pour, TotalBoat's own blog drops it to half an inch.
- EcoPoxy FlowCast: 0.5 to 1.5 inches for pours up to 30 liters.
- System Three RiverCast: 1.5 inches.
- UltraClear Deep Pour and Alumilite Amazing Deep Pour: 2 inches, though UltraClear would rather you do 1-inch layers 12 hours apart.
- TotalBoat ThickSet Fathom: 3 inches for castings under a gallon mixed, 2 inches for river tables.
- MAS Deep Pour X: up to 3 inches.
- Superclear Liquid Glass: "2-4 inches," says the product page title. More on that page in a minute, because it argues with itself.
That's an 8-to-1 spread for products that sit on the same shelf and get poured into the same kind of slab. And there's no standards body behind any of it. Every number is a manufacturer grading its own homework.
It's a Mass Rating in a Depth Costume
Epoxy cure makes heat. Heat makes epoxy cure faster. Faster cure makes more heat. That feedback loop is the whole story. WEST System's tech magazine Epoxyworks demonstrates it vividly: a gallon of epoxy left in one container can solidify in roughly five minutes, and 70 grams of their 105 Resin/206 Hardener concentrated in an 18-ounce bottle hit 410°F and cracked the container. That's an abusive demo, but the chemistry is the same. And two competitors publish the same math: MAS says doubling the mixed mass will likely cut your gel time in half, and raising the temperature 18°F cuts it in half again; WEST System says every 18°F increase halves pot life.
Read the fine print on any depth rating and you find a mass rating:
- MAS Deep Pour's limit doubles when you mix half the kit. MAS also caps mixing at one gallon, period.
- ThickSet's 2 inches collapses to half an inch the moment the casting is a river instead of a coaster.
- Fathom's 3 inches holds only "using less than 1 gallon of mixed epoxy."
- EcoPoxy's 1.5 inches assumes a 65–75°F room, under 20 liters poured, and a fan running on the project. A max rating that assumes forced-air cooling is telling you something.
FGCI, the company behind Superclear, states the rule outright: the more volume or the thicker the pour, the cooler your ambient temperature needs to be. MAS tells you to pour large slabs thinner than small castings, and marks the point of no return: "If the mixed material starts to get warm, that's your last warning." Smoking resin, in MAS's words, is thermal mass exceeding the thermal transfer rate.
The vendors aren't disagreeing about chemistry. They're disagreeing about which scenario they're quoting. The half-inch numbers are quoting your river table. The big numbers are quoting a coaster.
Same Building, Two Answers
Proof it's formulation, not marketing nerve: both kinds of numbers come from the same companies. MAS sells Deep Pour, at half an inch to 1, right next to Deep Pour X at 3 inches. TotalBoat sells ThickSet, half an inch for rivers, next to Fathom at 2. TotalBoat says it plainly: different formulations generate heat at different rates.
What the deeper rating buys is a slower hardener, and the bill comes due in time. Deep Pour X: 12-hour working time, 36-hour cure. Fathom: 4 to 6 hours to work, 5 to 10 days to full cure. FlowCast: 3 days before demolding, up to 14 to full cure. RiverCast: one hour to work, then seven days in the mold. Tabletop epoxy, which TotalBoat rates at an eighth to a quarter inch per pour, is the other end of the spectrum. Thin and fast, or deep and slow. Nobody sells deep and fast.
My favorite detail sits on Rockler's Deep Pour X listing: 3-inch pours cure in 24 to 36 hours at 70°F, but 2 inches or less can take up to 72. These formulas need their own exotherm to kick — MAS sets a 2-inch minimum casting thickness for Deep Pour X, and Fathom requires layers at least 1 inch deep. They aren't better epoxies. They're the right tool for exactly one job and the wrong tool for most others.
The 70-Degree Window
Temperature is the second dial, and it cuts both ways. Cold resin thickens and traps bubbles; FGCI says their epoxy may start to thicken under 65°F. A warm shop feeds the loop. The published windows are narrow: 60–75°F for MAS Deep Pour, 60–80 for Deep Pour X with a hard do-not-use above 85, 60–80 for Fathom with 70 "strongly recommended," 68–77 for FlowCast materials, 70–80 for System Three, 70–84 for FGCI. Stack them and exactly one temperature sits inside every window: roughly 70°F.
I live in Austin. An un-air-conditioned Texas garage doesn't hold 70°F between May and October, and by August it blows past MAS's 85°F cutoff before lunch. Pour deep in that without climate control and you're re-running the WEST System bottle demo with more resin. Condition the shop, the resin, and the slab, or wait for a cool front. This is football-weather work, not two-a-days work.
The Four-Inch Question
Superclear's Liquid Glass carries the biggest number on the market, and its own product page can't keep the story straight. The title says "Up to 2″-4″ Thick Per Pour." The description on the same page says 2 to 6 inches. FAQ text on that same page says up to 1 inch per pour depending on ambient temperature and total mass — wording that looks borrowed from their faster variant, but there it sits. Their beginner's guide lands on anywhere from half an inch to 4, with the honest caveat that warmer temperatures and larger volumes require thinner pours.
I don't think Superclear is lying, exactly. The 4-inch figure is the best case, modest volume in a cool stable room, quoted the way the half-inch vendors quote the worst case. But the company never publishes the mass-and-temperature table that would make the claim checkable, so you're doing the physics yourself. When a 2-inch vendor and a 4-inch vendor describe the same chemistry, believe the fine print, not the headline.
What the River Actually Costs
Deep-pour pricing only makes sense per cubic inch, so I ran the numbers myself: a US gallon is 231 cubic inches, and MAS's stated 300-cubic-inch yield from a 1.3-gallon kit confirms mixed volumes are additive. The arithmetic is mine, not the vendors'.
| Product | Single-pour rating | Kit | Price | ~$/cu in |
|---|---|---|---|---|
| TotalBoat Fathom | 2″ rivers, 3″ small | 3 gal | $229.99 | $0.33 |
| EcoPoxy FlowCast | 1.5″ (fan, under 20 L) | 12 L | $249.96 | $0.34 |
| Superclear Liquid Glass | "2–4″" | 3 gal | $239.99 sale | $0.35 |
| System Three RiverCast | 1.5″ | 1.5 gal | $179.95 | $0.52 |
| MAS Deep Pour X | 3″ | 1.5 gal | $185.99 | $0.54 |
| MAS Deep Pour | 0.5–1″ | 1.3 gal | $169.99 | $0.57 |
| Alumilite Deep Pour | 2″ | 24 oz | $51.99 | $1.20 |
MAS Deep Pour pricing is Rockler's retail; the rest are the makers' own stores. Superclear's $0.35 is a sale price and climbs to about $0.43 at its regular $299.99. Small kits are brutal: Alumilite's 24-ounce craft kit runs two to four times the big-kit rate. Volume wins: Fathom falls to about $0.32 in the 6-gallon size, FlowCast to $0.30 at 30 liters.
Now scale it. A 6-foot slab with a river averaging 6 inches wide, poured 1.5 inches deep, needs 648 cubic inches, call it 2.8 gallons mixed. That's the $230 Fathom 3-gallon kit, or $320–370 in Deep Pour X or RiverCast. An 8-footer with an 8-inch river at 2 inches needs about 1,536 cubic inches, roughly 6.6 gallons: TotalBoat's $450 6-gallon kit, or $570 and up in MAS X. An ordinary dining-table pour is a $250-to-$600 bet riding on one exotherm, and MAS's published failure list for blowing it — yellow, distort, shrink, crack — takes all of it at once.
A half-inch product can build any depth in layers — MAS wants each lift cooled to room temperature and fingernail-tested first, plus a seal coat on the wood so trapped air doesn't bubble up through the pour. But the clock is real: 12 hours between lifts for UltraClear, about 24 for EcoPoxy, 36 to 48 for Fathom. A 2-inch river in half-inch lifts adds roughly a week of shop time over one lift of Fathom or Deep Pour X. Start that schedule Labor Day weekend and you're still watching resin gel at kickoff.
So here's how I'd buy. Figure your cubic inches first: length times width times depth, fourth-grade math, and it's the whole game. Under a few hundred cubic inches, nearly anything on the list works and the cheap kit wins. For a real river at 1.5 to 2 inches, buy the product whose fine print, not headline, covers your mass at your depth. Hold the shop at 70. Pour once. And remember who wrote the number on the front of the jug. The label is marketing. The instruction sheet is chemistry. Chemistry wins every time.