Intumescent Coatings

In commercial construction, intumescent coatings are commonly discussed when a solution more unique than standard fire-rated floor or wall assemblies is required to maintain fire-rating continuity.  Intumescent paints and mastics are coating technologies that utilize char formation to prevent fire spread.  Intumescent coatings can swell up to 100 times their initial thickness upon exposure to fire heat.  These coatings are activated between 300°F and 400°F.  Intumescent coatings often allow architects to expose building structure when fire protection of the structure is required by building code.

When these coatings heat up, they expand to form carbon foam that resists the transfer of heat.  The specific heat of graphite (pure carbon) is very high, therefore it takes a great deal of heat to increase its temperature. 

In addition to expanding as non-combustible mass upon exposure to fire, intumbescent coatings also off-gas.  Upon expanding, they leech oxygen away from the substrate.  A lower-oxygen environment is less combustible, further increasing fire spread protection.

In the event that a fire occurs, the substrate beneath intumescent paint is often salvageable.  The expanded coating is scraped off and the surface beneath can be repainted.

There is a difference between intumescent paint and intumescent mastics.  Intumescent paints provide minimal fire ratings.  They are often rolled or brush applied similarly to household paint.  However, some manufacturers recommend spray application.  Intumescent mastics are typically trowel applied in 1/8” to 3/8” thickness and provide fire ratings of 45 minutes to 2 hours.

Underwriters Laboratories [UL] categorize intumescents as fire retardant coatings.  They divide coatings intended for application onto building materials into two categories:  “fire retardant” and “general purpose.”  In order to be a fire retardant coating, it must reduce the flame spread of douglas fir and other tested interior substrates by at least 50%.

Intumescent coatings should not be top coated with an incompatible paint that will prevent the necessary chemical reaction from occurring.  Also, architectural details often must allow adjacent space to be clear of additional materials or connections so the material may expand as required.

The earliest developed intumescent coatings were sensitive to moisture over time and required re-application.  New intumescents have overcome this limitation, and can last for several years.  However, as with any coatings, periodic touch-up and recoating are necessary.

Proper surface preparation should be performed prior to intumescent coating application.  This is more critical for intumescents than for standard finishes.  Several manufacturers refer to the SSPC: The Society for Protective Coatings publications for surface preparation standards.

These coatings must be applied as recommended by the manufacturer.  Unlike typical paint coatings, failure to properly apply fire resistant intumescent coatings can endanger the safety of the building occupants.  The coating must be applied evenly at the recommended spreading rate.  The spreading rate is similar to that of corrosion resistant coatings.  Most manufacturers listed in UL require two coats.  However, some systems indicate compliance with a single coat, but lesser rate of coverage per gallon.

The final appearance of intumescent coatings is similar to standard paint finishes.  The resulting finish is two to four times as thick.  They are available in pigmented and clear finishes.  Recoating may be required after 3 to 5 years depending on the substrate and interior environment.

Comments

[Stone Restoration]

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Stone Restoration