“Three Common Questions About W-Rated Firestop Sealants”

Brush up on what W-ratings mean, how they’re obtained, what they mean for firestop sealants, and more.

by Jeff Hamilton

Many professionals are familiar with firestop sealants, but not all know why and when to use W-rated sealants. While most sealants are designed to protect against the spread of flames, smoke, and gas between floor and wall through-penetrations, W-rated sealants offer an added barrier against moisture.

Following are answers to some commonly asked questions about W-rated sealants.

1. What is a W-rating?

A W-rated sealant is one that, after fully curing, has been tested under 3 feet of water pressure. It must remain submerged for 72 hours without leaking to receive the rating.

These guidelines are outlined in the UL 1479 safety standard, which lists W-ratings as optional to firestop system compliance. But for some applications, such as where moisture may be present, a W-rated sealant can help protect your work and the work of other professionals alongside you. No one wants to show up on the jobsite to find their efforts damaged by a sudden rain shower, high humidity, or pipe leak.

2. When are W-Rated firestop sealants needed?

For some jobs, W-rated firestop systems are listed in the engineer’s or architect’s specifications. Many times, they are specified for every third or fourth floor of a high-rise building.

Even if they’re not specified, W-rated sealants are practical in regions where humidity and rainfall are common. The sealants help with the possibility of sudden rain showers or storms during the construction process and can protect components like drywall, carpentry, and electrical work in floors below the penetration.

Similarly, W-rated sealants can protect parts of the building where moisture may be present before and after the build is complete, such as bathrooms or kitchens. They provide a layer of protection for the floors below in the event of a pipe leak.

Not all sealants are W rated, so check the manufacturer’s specifications to see if a sealant has undergone a water-leakage test based on UL guidelines.

3. Are all W-rated firestop sealants waterproof?

There are two kinds of W-rated sealants on the market—water-based and silicone. Water-based sealants are often more affordable, but when you need quick cure times, a silicone sealant is the way to go.

This is because if water reaches a water-based sealant before it is cured, the sealant will wash away and cause leaks. This could cause damage to the floors below where drywall may be installed. These sealants can take up to a month to cure depending on sealant depth.

A silicone firestop sealant, on the other hand, is much better at repelling water than a water-based intumescent sealant, and its cure time is only three days, giving it waterproof capabilities sooner and to a greater degree than water-based sealants.

If your application could be exposed to humidity, rain, or even pipe leaks before or after the building is complete, a silicone sealant may be the best choice. Your sealant selection can help protect the longevity of not only your work, but also the work of the other pros on the jobsite.

About the Author

Jeff Hamilton is the firestop product manager at RWC—a market leader and manufacturer of water control systems and plumbing solutions for residential, commercial, and industrial applications. Learn more about the differences between firestop sealants and how to choose the right one for the job by visiting HoldRite’s guide to firestop sealants.

The opinions expressed in this article are those of the author and not the American Society of Plumbing Engineers.

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