Spray Foam - the curing process and the three E's

Spray Foam – the Curing Process and the Three E’s

You might ask, “How long does spray take to cure?”

The answer is a few hours.

Spray foam will be tack-free within 20-30 seconds and it’ll rise to completion to where you can walk on it within a couple of minutes.

Spray foam has an off-gassing period of a few hours until it’s 100% cured.

Now that we got “curing” out of the way, let’s begin with how spray foam is laid down.

This article has been edited and approved for publishing by a spray foam roofing expert with more than 30 years of experience.

Let’s get started!

How does spray foam get installed?

Spray foam is the reacted product of two components, an “A” side, and a “B” side, that are mixed and sprayed onto a roofing substrate.

In general, a spray foam roofing contractor must be capable of storing, pumping, heating, mixing, and spraying these two components at the material supplier’s recommended temperature, viscosity, and material ratio. (Spray Polyurethane Foam Alliance)

Once the foam is sprayed correctly, a curing process must occur before applying the coating.

NOTE: Coating MUST be applied to spray foam due to UV lighting, which degrades spray foam within 72 hours.


When will spray foam be “tack-free”?

After the foam is sprayed, the first step in the curing process is the point when spray foam is tack-free.

Tack-free is the time that the surface of the foam can be touched with a wooden stick without it sticking.

This usually takes 20-30 seconds.

After 20-30 seconds, spray foam will begin to develop its waterproofing skin and is very close to being walkable.



When can you walk on a spray foam roof?

Spray foam reacts quickly and evolves into a walkable surface within 1-2 minutes after it’s sprayed.



Can temperature affect curing? If it’s hotter, does it cure quicker?

Temperature not only affects how long spray foam takes to cure; it greatly affects how spray foam is laid down.



For Spray foam to be laid down correctly, it needs three types of energy:

  1. Electrical – the equipment used in mixing/heating foam
  2. Environmental – the air temperature, deck temperature, sun, etc.
  3. Exothermic – the heat created from the chemical reaction when the A and B components meet

You need all three energies synced for the foam to be installed and to cure correctly. Here’s an example of how changing energies can affect a spray foam job:

Say it’s October, and you have a regular speed of foam that’s meant to be used in 65-90 degree ambient air temperature. Today it’s 60 degrees, so you’re at the bottom end of that speed of foam.

Two energies are lacking:

  • Environment – the air temperature is below what’s recommended (not controllable)
  • Exothermic – the chemical reaction will be too slow because the foam was meant to operate in 65-90 degree weather (controllable)

Solution: A roofing contractor will need to increase the amount of heat used in the equipment to mix the A and B sides. Also, you may need to order a faster-reacting foam to increase the exothermic energy.

The point is that the environment is never controllable, the other two can be by adjusting equipment temperatures or using a faster or slower speed of foam.



You mentioned coating. How long does that take to cure?

It all depends on the weather. On a good, warm day, it could be tack-free in 15-20 minutes and be able to walk on within an hour.

On a colder day with no sun, it can take 3-4 hours for the coating to cure.




Hopefully, today you learned that spray foam cures 100% within a few hours. It’s capable of being walked on within a couple of minutes, but the “off-gassing” period can last a few hours.

Also, we hope you learned a little science today in learning the three energies that are needed for spray foam to be laid down correctly.

Other related articles:


The spray foam roofing cheat sheet - download now


  • Greg Palya

    Greg Palya is the Digital Content Manager of West Roofing Systems, Inc. He has a B.S. in Marketing from the University of Akron and an MBA in Marketing from Walsh University. You can find him on the basketball court or golf course when he's not trying to teach others about spray foam roofing and silicone roof coatings.

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