FS4 Fireshield AC Intumescent Sealant – 310ml Review

A go-to fire sealant for contractors who need to get it right

We’ve supplied a lot of intumescent products over the years, but the FS4 Fireshield AC is one of the most reliable when it comes to firestopping joints and voids in construction. Whether you’re sealing around cables, floors and ceilings, or drylining systems, this one just works, and more importantly, it holds.
It’s a flexible, acrylic-based sealant that expands when exposed to high temperatures. That swelling creates a tough, charred barrier that helps contain smoke and fire. We’ve seen it used in everything from office builds to healthcare projects and it’s always performed well when applied properly.

Easy to work with, and quick to finish

The FS4 Fireshield AC Intumescent Sealant is solvent-free, non-shrinking, and cures to a clean, paintable finish. It skins over quickly, which makes it practical for jobs with tight turnaround times, and it can be over-painted in about an hour using fire-rated paint.
It’s certified to EN1366-3, EN1366-4, and EN ISO 10140-2, and under the right conditions, it offers up to four hours of fire protection. That depends on how it’s applied, the depth, and the materials you’re sealing, so if you’re unsure, just ask us.
We’ve had customers switch to this from more expensive options because it’s just easier to apply and gives them peace of mind on inspection day.

Things to keep in mind

It’s important to note that this sealant is not magic, the fire rating is dependent on proper application. A shallow bead in the wrong type of joint won’t perform the way it’s supposed to.
Also, while it’s flexible, it’s not designed for areas with significant expansion or structural movement. For those, we’d typically recommend a more elastic, purpose-built sealant.
Occasionally, due to stock rotation, we may send out a like-for-like product from a different manufacturer, but performance and compliance are always equivalent.

Common questions we hear from customers

Can I use this around cables and pipes?

Yes, it’s one of the most common applications. It’s designed to seal around penetrations and stop fire from travelling through them.

Is this suitable for use indoors?

Absolutely. It’s solvent-free, low-odour, and safe to use inside buildings.

Can I paint over it?

Yes, you can paint over it with fire-resistant paint about an hour after application.

How do I get the 4-hour fire rating?

The key is proper joint prep and depth of sealant. We can help you check the right thickness for your use case.

Written by Enya Kerry – Office Manager at Ducting Express

Hi. My name is Enya Kerry. I am the Office Manager at Ducting Express. With over four years of experience and certifications in W201 and P601, I help our customers every day with practical advice on fire safety, ducting systems, and extraction setups. If you’ve got a project coming up and you’re unsure which product is right, feel free to get in touch.