Epoxy Recoat Window Calculator

Scale the recoat window on your data sheet for the slab in front of you, and see whether recoating now is too soon, inside the window, or too late.

When Does the Recoat Window Open and Close

A data sheet quotes its recoat window at one temperature, and your slab is almost never at it. Enter the earliest and latest recoat from the sheet, the temperature the sheet quotes them at, and the slab temperature through the wait. The tool scales the window for the slab and, if you add the hours since the last coat, tells you whether recoating now is too soon, inside the window, or too late.

Your data sheet comes first. Enter the recoat window exactly as your product's Technical Data Sheet (TDS) states it. If the sheet gives a window for your temperature, use that instead of a scaled estimate.
Temperature Unit

From the Data Sheet

The recoat window and the temperature it is quoted at. Both are on the same line of the sheet, or close to it.

The minimum. A sheet in minutes: divide by 60.
Leave blank only if the sheet states no maximum.
Often printed as a footnote to the timing table.
Common:
The sheet's lowest substrate temperature. Below it, no window applies.

On Site

The slab, not the air: take it with an infrared thermometer. On a cooling slab use the coolest it will reach during the wait; on a hot one, check against the warmest.

Through the wait between coats, not just this morning.
Add it for a verdict on recoating now.

Enter the earliest recoat, the temperature the sheet quotes it at, and the slab temperature to see the window.

The window is scaled from the values you enter by the standard rule that cure speed roughly doubles for every 10°C (18°F) of warmth, the same model as the cure time calculator. Film thickness, air movement and humidity also move it. The data sheet wins wherever it gives a figure for your conditions.

How the Epoxy Recoat Window Calculator Works

  1. Enter the earliest and latest recoat times from the data sheet, in hours
  2. Enter the temperature the sheet quotes them at (70°F and 77°F are the most common)
  3. Optionally add the sheet's minimum application temperature
  4. Enter the slab temperature through the wait between coats, taken with an infrared thermometer
  5. Add the hours since the last coat went down to see a verdict on recoating now

Examples

ScenarioA sheet that says 12 to 24 hours at 77°F, checked the next morning on a cold slab (illustration, not a product)Input12 to 24 hr at 77°F · slab 59°F · 16 hr since the last coatResultThe window is 24 hr to 48 hr. Too soon: it opens in about 8 hr
ScenarioThe same sheet with the slab at the sheet's own temperatureInput12 to 24 hr at 77°F · slab 77°F · 16 hr since the last coatResultThe window is 12 hr to 24 hr, exactly as printed. Inside it, with about 8 hr left
ScenarioThe same sheet on a hot slabInput12 to 24 hr at 77°F · slab 95°F · 16 hr since the last coatResultThe window is 6 hr to 12 hr. Too late: it closed about 4 hr ago, so abrade before recoating

Frequently Asked Questions

What is a recoat window?

The period after one coat goes down during which the next coat can go on and bond to it chemically. It has two edges. Before it opens, the coat underneath has not cured far enough to take another layer. After it closes, the coat underneath is too far cured for the next one to bond into it, and the bond has to be made mechanically by abrading the surface first. The data sheet gives both edges, at a stated temperature.

Why does the window move with temperature?

Because cure is a chemical reaction and its speed depends on temperature. The working rule, and the one this tool uses, is that cure speed roughly doubles for every 10°C (18°F) of warmth and halves for every 10°C of cold. So a slab one step colder than the sheet's reference temperature doubles both edges of the window, and a slab one step warmer halves them. The same overnight gap can be too soon on a cold slab and too late on a hot one.

Which temperature should I enter, the air or the slab?

The slab, because that is the temperature the coat is curing at. Take it with an infrared thermometer, and enter the temperature through the wait rather than one reading. A slab cools overnight and lags the air by hours, so a warm afternoon reading overstates how fast the floor will cure before you come back to it: for the opening edge, use the coolest the slab will reach. On a hot slab the closing edge is the risk, so check it against the warmest.

My data sheet gives a table of recoat times by temperature. Do I still need this?

Use the table wherever it covers your conditions. A manufacturer's figure for a temperature is measured on that product, and it beats any general rule, including the one this tool runs. The calculator is for the much more common sheet that gives one window at one temperature, and for checking a temperature that falls between two rows of a table.

What if the window has already closed?

Then the next coat needs a mechanical bond rather than a chemical one, and the data sheet will say how to get it, usually by abrading the whole surface to a uniform dull finish, cleaning it and then recoating. Intercoat delamination covers the repair in full. What does not work is recoating as if the window were still open, because the floor will look perfect until the top coat lets go.

Why is nothing pre-filled?

Because the window belongs to your product, and recoat windows differ widely between chemistries, between products and between the fast and slow versions of the same product. This site does not publish generic recoat times. The examples on this page use an illustration sheet, labeled that way, to show how far temperature moves a window.

Important Notes

  • Nothing is seeded. The window, its reference temperature and the minimum temperature come off your data sheet.
  • The scaling is the standard rule that cure speed roughly doubles for every 10°C (18°F), the same model the cure time calculator uses.
  • Enter the slab temperature through the whole wait: the coolest it reaches for the opening edge, the warmest for the closing edge on a hot slab.
  • Film thickness, air movement and humidity also move cure. A heavy coat or a still, humid room can open the window later than the tool shows.
  • When the slab is more than 10°C (18°F) from the sheet's temperature the tool flags it. That limit is our caution, not a published standard.
  • Where the data sheet gives a figure for your temperature, the data sheet wins.
Cure Time CalculatorThe same temperature model applied to pot life, foot traffic and return to service.Dew Point CalculatorA slab cooling overnight between coats can drop toward the dew point. Check it before the next coat.Film Thickness CalculatorA coat laid heavier than planned cures slower through its depth than the sheet assumes.
Epoxy Recoat Windows: Reading the Sheet and Scaling It for the SlabA recoat window is printed at one temperature and used at another. How to read it off the data sheet, scale it for the slab, and plan the gap between coats around it.Applying Epoxy in Cold WeatherThree temperatures decide a cold day and the thermostat shows none of them. Why the slab lags by hours, and why kits run short.How to Read a Coating Technical Data SheetA data sheet is not a list of numbers, it is a list of conditions. Field by field, and the six ways a sheet gets misread.Intercoat Delamination: When One Coat Lets Go of AnotherThe underside of the flake settles this in about two seconds. Concrete on the back means the bond to the slab failed and you are on the wrong page. Coating on the back means the layers never bonded to each other, and that is almost always a recoat window that closed before anybody expected it to, or something invisible sitting on the surface when the next coat went down.Wrinkling and AlligatoringA wrinkled floor is a film that set at two different speeds. The surface skinned over while the material underneath was still moving, and the skin buckled rather than stretched. Nearly every case comes down to one of three things: the coat was too thick, the surface was heated far faster than the body, or it was recoated before the coat beneath it had finished.