Easy Epoxy Calc

How much working time does epoxy have at 90°F?

Short answer

At 90°F, epoxy with 40 minutes of working time at 70°F gives you only about 19 minutes — about 2.2× faster — and a 3-hour recoat comes down to about 1.4 hours.

How to work it out

  1. 70 °F − 90 °F = -20 °F → 2^(-20 ÷ 18) = ×0.46
  2. 40 min × 0.46 = 19 minutes; recoat 3 h × 0.46 = 1.4 hours; full cure 7 days → 3.2 days
  3. From 9:00 am: working time ends ~9:20 am → recoat from 10:25 am → full cure ~3:00 pm (+3 days) (rounded to 5 minutes; full cure to the hour)

A summer garage or a shop with the sun on the door is where flood coats go wrong: the batch starts to thicken while you’re still spreading, and a full bucket can set far faster than even this estimate because it heats itself. This example uses TotalBoat TableTop’s figures (40 minutes and 3 hours at 70°F); 90°F is 20°F above that and 10°F above TotalBoat’s 65–80°F range. Mix smaller batches, pour them out of the bucket straight away, and don’t pour a deep-pour resin at its maximum rated depth in this heat — a warm deep pour behaves like a deeper one.

Adjust for your project

Each kind of epoxy has very different times. The listed ones use that maker’s published figures; for any other product, pick “My own label”.
°F
Where the piece will sit while it cures. If the surface is colder than the air, enter that below too — the colder one sets the times.
°F
The tabletop, slab or floor itself — an infrared thermometer reads it in a second. Concrete and wood from a cold shop are often colder than the air.
%
Relative humidity from a hygrometer or the weather app. Used to check the dew point — the temperature at which moisture starts to form on a cold surface.
Pick from the list (half-hour steps). The schedule below counts on from this time; “+1 day” means the next day.
°F
Printed next to the times — usually 70–77°F (21–25°C).
min
Also called pot life: how long the mixed epoxy stays runny enough to pour and spread.
hours
How soon you can pour or brush the next coat. Labels may say “recoat after” or “tack-free”.
days
When it’s hard enough for normal use.
°F
Optional — leave blank if the label doesn’t list one.
More options: recoat by · demold
hours
Some labels give a recoat window. After this, scuff-sand the surface before the next coat so it grips. Leave blank if yours doesn’t say.
hours
For castings and river tables: when it can come out of the mold (the form you poured into). Leave blank for a coating.
Estimated at your temperatureRecoat after about 1.4 hours · 19 minutes to work
Your schedule (clock times)
Mix 9:00 am → working time ends ~9:20 am → recoat from 10:25 am → full cure ~3:00 pm (+3 days)
Estimated working time
19 minutes
Earliest recoat / next layer
1.4 hours
Estimated full cure
3.2 days
Compared with the label
About 2.2× faster
  • Warm shops shorten working time sharply, and a thick pour or a full bucket gets hotter still. Mix smaller batches, get it out of the bucket quickly, and don’t pour deep-pour resin at its maximum depth in a hot room.
  • The rule is a rough guide for the resin at room temperature in a thin film. A mixed batch left in the cup heats itself and sets much faster than the estimate — pot life on most data sheets is measured on a small mass in a cup.

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Infrared thermometerCheck the surface you’re pouring on as well as the air; a sunlit or freshly warmed surface speeds the cure beyond what the room suggests.
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At 90°F: working time for products with different label pot lives

At 90°F: working time for products with different label pot lives
Label working timeEstimated working timeEarliest recoat / next layer
15 min on the label7 minutes1.4 hours
20 min on the label9 minutes1.4 hours
30 min on the label14 minutes1.4 hours
40 min on the label19 minutes1.4 hours
60 min on the label28 minutes1.4 hours

What to know about pouring epoxy at 90°F

  • 90°F is above most label ranges. TotalBoat lists 65–80°F for its TableTop epoxy, and MAS says not to use Deep Pour X above 85°F at all. Heat doesn’t stop the cure, but it takes away the margin those ranges are built around — for a deep-pour resin that can mean cracking, yellowing or a smoking pour.
  • The label pot life was measured on a small cup. Epoxyworks measures pot life on a 100 g mass. A half-gallon batch for a tabletop flood coat traps its own heat, so in a hot room it can set well before the estimate above. Mix only what you can spread in a few minutes and get it onto the surface — a thin layer loses heat and stays workable longer than the same resin in the bucket.
  • Warm wood breathes out air. A tabletop that warms up during the pour (sun through a window, a rising afternoon temperature) releases air from its pores as bubbles. Pour in the morning or evening when the temperature is steady or falling, and seal-coat bare wood first.
  • Start early and the day works for you. Mix at 7:00 am and, at these figures, the next coat is ready by about 8:25 am — before the afternoon peak. Pick your start time in the calculator to see the clock times.
  • Shorter recoat windows cut both ways. If your label gives a latest-recoat time, that shrinks by the same factor — miss it and you’ll need to scuff-sand before the next coat. Enter it under More options to see the window as clock times.

If your shop swings the other way in winter, compare how long epoxy takes to cure at 60°F and will epoxy cure at 50°F.

Different size? Use the full Epoxy Cure Time & Temperature Calculator.

What you’ll need

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Frequently asked questions

How much working time does a 20-minute epoxy have at 90°F?

About 9 minutes on the surface — and less in a full cup. Fast resins are hard to flood-coat with in this heat; mix very small batches.

How much working time does epoxy have at 95°F?

About 15 minutes for a product rated 40 minutes at 70°F — about 2.6× faster than the label. That’s well above most label ranges; wait for a cooler part of the day if you can.

How much working time does epoxy have at 85°F?

About 22 minutes instead of 40 — about 1.8× faster than the label. 85°F is the upper limit MAS gives for Deep Pour X.

If I mix at 7 am on a 90°F day, when can I recoat?

From about 8:25 am — 1.4 hours after mixing, for a label that says 3 hours at 70°F.

Other common sizes

Sources