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

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

If you really want to know how long spray foam takes to cure, the answer is a couple 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 also has an off-gassing period of a couple hours until it’s 100% cured.

Now that we got curing times out of the way, let’s first begin on how spray foam is laid down.

A quick overview on how spray foam gets laid down

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

NOTE: coating MUST be applied to spray foam due to UV lighting, which deteriorates spray foam immediately.

When will spray foam be “tack-free”?

After 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 within 20-30 seconds.

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

When can you walk on a spray foam roof?

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

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

Buckle your seat belts, it’s about to get Big Bang Theory in here.

Temperature not only effects 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 foam to be laid down (and 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.

There are two energies that 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 side. 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 of slower speed of foam.

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

It all depends on the weather. On a good, warm, windy 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.

Curing of the post

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.

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