Mastic or foam for door sets? Our guide to choosing the right product (and avoiding the wrong one)

One of the most common questions we’re asked is whether installers should use mastic or foam around fire door sets. The short answer is that either could be the right choice – but only if it’s been tested properly, is meant for that exact job, and meets the standards it claims to. Sounds simple, but this is where a lot of installations go wrong.

Most fire certifications usually state the facts clearly, but it’s often overlooked. They say something along the lines of:

“Door assemblies shall be installed as stated in BS 8214, Table 2. Suitable CERTIFIRE approved lineal gap sealing systems may also be utilised to protect the frame/supporting construction gap, subject to the conditions contained within the relevant certificate.”

The emphasis is on the last line – ‘subject to the conditions’. BS 8214 makes it clear that any linear gap sealing product can be used, as long as it has been tested to one of four specific fire test standards. Those are:

• BS 476 Part 22
• BS 476 Part 31.1
• BS EN 1634-1
• BS EN 1634-3

If a product hasn’t been tested to at least one of these, it shouldn’t be used. But alongside this, the installer must check whether the product is actually suitable for the situation on site. Foams and mastics aren’t automatically interchangeable, and the restrictions – which might only be found in their certifications – really matter. If an installer doesn’t check, they not only risk being non-compliant – but risk undermining the efficacy and safety of the fire door they’re installing.

Our step-by-step advice

To help clear up the confusion, we always give the following advice. It’s a simple step-by-step guide for when installers aren’t quite sure whether it’s mastic or foam they should be using, ensuring the product is fire-tested and being used correctly.

Step 1 – Check that the product is tested to one of the four standards

Don’t rely on what’s written on the can or even on a data sheet. Always request the full fire certification for the specific product. This is the only place where the valid test standard is confirmed.

Step 2 – Check the certification to confirm it can be used for the intended purpose

Some products are tested only for wall expansion gaps and cannot be used for door sets, even if they appear ‘fire rated’. Certification will clearly state whether door assemblies are included or not.

Step 3 – Check the certification for any special rules or restrictions

This is where we find that things often go wrong. The certification may set maximum and minimum permitted gaps, restrict the type of frame or wall construction, or specify what kind of packers can or cannot be used. Again, these rules are rarely printed on the product and can only be found in the certification document. Without checking the certification, the installation could be non-compliant.

Common misconceptions to avoid

When you’ve worked in the industry as long as we have, you start to come across the same misconceptions time and time again. Here are a few of the most common misconceptions that could lead you to non-compliance.

Assuming a product is suitable because it says FD30 or FD60 on the tube

That doesn’t guarantee it can be used with fire door sets. Only the certification can confirm that.

Assuming one product works for all gap sizes

Every foam or mastic has its own limits. Some are unsuitable for use for gaps under 5mm while others have upper limits. Using the wrong product on the wrong gap size can invalidate the installation.

Assuming all products work with all packers

Some foams cannot be used with plastic packers while others require non-combustible packers. Again, only the certificate will tell you which is acceptable.

These simple misunderstandings can lead to serious consequences. Doors may fail inspection, need to be completely reinstalled, or in the worst-case scenario fail in a real fire and risk lives.

Why this matters so much

In the last year, we’ve seen some installers seeking to push this decision back onto manufacturers like us, by asking us to tell them which product to use. But it simply doesn’t work like that. The installer must have the competence to choose the right sealant, and they can do that by following the steps above.

Ultimately, the person fitting the door is solely responsible for ensuring the sealant they use is tested and compliant.
If a non-compliant product is used and later found during an inspection, it’s the installer who will be questioned and asked to prove that they followed the certification, standards, and manufacturer’s guidance.

Where we can help

At Stairways, we’re always happy to help clarify requirements, but the certification remains the ultimate reference point. When installers really understand the products they’re using and what they can and can’t do, confusion and mistakes can be avoided. In doing such a safety-critical job as installing a fire door, installers cannot be anything less than 100% certain.

Want to chat more about this? Reach out today.