- Niky Baker
- Apr 28
- 2 min read

Why Using the Right Sealant or Mastic in Fire-Rated Windows and Doors Actually Matters
When it comes to fire-rated windows and doors, most people think about the glass, the frame, or maybe the fancy intumescent strips that swell up when they get hot. But one thing that often flies under the radar — and honestly shouldn't — is the sealant or mastic used around those installations. Believe it or not, that little bead of goo can make a massive difference between a fire staying contained... or chaos breaking loose.
Let's get one thing straight
You can't just grab the cheapest tube of sealant from the hardware store and slap it on a fire-rated window or door. Regular silicone or acrylic sealants aren't designed to stand up to high temperatures. In a fire, they'd melt away faster than a chocolate bar on a dashboard, leaving big gaps where smoke, hot gases, and flames can shoot through.
Fire-rated sealants and mastics, on the other hand, are specially formulated to either resist burning, expand when heated, or do both. They maintain the integrity of the fire barrier, giving people more time to get out safely and giving firefighters a better chance to control the blaze.
It's About the Whole System
A fire-rated door or window isn't just about one tough component. It's a system — and every part needs to work together. The glass, the frame, the door leaf, the hinges, the locks, the sealant... all of it is tested as a unit. If you swap out a certified fire-rated mastic for something else, you're basically breaking the system. And if the worst happens, that could mean faster fire spread, more damage, and even risk to lives.
Worse still, in commercial settings, using the wrong sealant can lead to inspection failures, legal headaches, and insurance claims being denied. No one wants to be explaining to a boss or a building inspector why they cut corners on a critical fire safety detail.
It’s Not Rocket Science (But It’s Important)
Choosing the right fire-rated mastic or sealant isn't hard. Most products clearly say "fire-rated" on the label, along with information about how many minutes of protection they offer (30, 60, 90 minutes, etc.). Such as Dowsil Firestop 700, Dowsil Firestop 400, Lorient Intumescent mastic,and Lorient acoustic acrylic sealant. Stick to the ones that have proper certifications (like BS 476, EN 1366, ASTM E814 — depending on your country) and check that they are approved for the specific application you're working on.
Also, make sure you're using it properly. Follow the manufacturer’s installation guidelines: thickness of the bead, joint size, curing time, all of it matters. A rushed or messy job can be just as bad as using the wrong product altogether.
Final Thought
At the end of the day, using the right sealant or mastic in fire-rated windows and doors is about doing the job right — and protecting people’s lives. It's a tiny detail that makes a huge difference. So next time you're reaching for a tube of something to finish up a fire-rated install, take a second and make sure you're using the good stuff. It's a small step that could have massive consequences if overlooked, and data sheets you may need are here https://www.fireprotect.co.uk/adhesives