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Calculators / Floors, heat and light

Can you coat the garage floor today?

Every garage floor kit has a temperature window, and some have a humidity limit and a dew point rule too. Put in today's conditions and you'll see each one checked, plus when you can walk and drive on it.

Updated · How we check our numbers

These are example numbers. Put in yours.

The coating

Coating

Right now

°F
°F

An infrared thermometer pointed at the slab. Leave blank and we use the air temperature.

%

From a hygrometer in the garage, or the local weather.

The forecast

°F

The overnight lows in your forecast.

°F
Rain or heavy dew forecast?

Good to coat

Yes, coat today

Rust-Oleum EpoxyShield (water-based kit): everything you entered is inside the maker’s limits. Wait 10 min before brushing, 15 before rolling; use it all within 1½ hours.

Allowed
60 to 85°Fair and floor
Dew point
54°Ffloor 14°F above
Humidity limit
below 80%
Cars on it
3 days

Estimate for planning only, not professional advice. Check the manufacturer’s instructions, your local code and a licensed professional before you buy, build or install. Use at your own risk. Terms.

dew point = Magnus(74°F, 50%) = 54.2°F

floor − dew point = 68°F − 54.2°F = 13.8°F

Against the maker’s limits

2-part water-based epoxy
  • Air temperature74°F; needs 60 to 85°F
    OK
  • Floor temperature68°F; needs 60 to 85°F
    OK
  • Humidity50%; needs below 80%
    OK
  • Floor above dew pointDew point 54°F; the floor is 14°F above it, needs 5°F
    OK
  • Low over the next 2 days66°F; must stay at or above 65°F
    OK
  • Light foot trafficAfter coating, at 70°F and 50% relative humidity
    12 to 16 hours
  • Normal foot traffic, heavy items backAfter coating, at 70°F and 50% relative humidity
    24 to 48 hours
  • Cars, and full cureAfter coating, at 70°F and 50% relative humidity
    3 days

Limits and times are copied from the maker’s data sheet and instruction sheet. Where the two disagree, we use the stricter.

Expect it to take longer

These times are for 70°F and 50% relative humidity. Allow more time at cooler temperatures.

Test the slab first

Tape a 2 × 2 ft plastic sheet to the bare concrete for 24 hours. Droplets under it, or darker concrete, means moisture is coming up and the coating won’t hold (Rust-Oleum, DRYLOK). New concrete needs about a month first.

How we work it out

Every limit comes from the maker's own data sheet or instruction sheet. When the two disagree, we use the stricter one: Rust-Oleum's EpoxyShield data sheet allows 85% humidity and its instruction sheet says below 80%, so we check 80.

The temperature window is for the air and the concrete. A slab warms more slowly than the air, so on a cool morning it can sit below the window while the garage feels fine. Measure the floor with an infrared thermometer.

The dew point is where water starts to condense. Rust-Oleum's 2-part coatings need the floor at least 5°F above it.

dew point = Magnus(air temperature, humidity), with the National Weather Service's constants

The forecast matters as much as today. EpoxyShield must not drop below 65°F for the next 24 to 48 hours. RockSolid must stay between 40 and 90°F, with no rain, for 48 hours. Most 1-part paints just need 50°F or warmer and no rain for a day.

Cure times are the maker's figures at the conditions they name, usually 70 to 77°F and 50% humidity. Colder or more humid, and every maker says it takes longer. Seal-Krete is the only maker that publishes times at 50, 77 and 90°F, so for it we read between those columns.

Where the numbers come from

Floor coating

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