Intumescent Strip Problems

Intumescent Strip Problems: Painted, Damaged or Missing Fire Door Seals

Fire door seals are easy to overlook until an inspection reveals something wrong. An intumescent strip may have been painted over during redecoration, pulled loose from its groove, damaged around the lock or hinges, or disappeared altogether. On a combined seal, the intumescent material may look intact while the smoke-control brush or fin is bent, clogged with paint or torn.

These are not all the same problem, and the answer is not always to pull the old seal out and fit something that looks similar. The first job is to establish what has happened and what sealing arrangement the door is supposed to have.

What should an intumescent strip look like?

On many timber fire doors, intumescent strips sit in grooves in the door edge or frame around the head and jambs. They should be secure, continuous where required and free from obvious damage. Combined fire and smoke seals will also have a brush or flexible fin projecting from the seal.

The exact arrangement varies between doors. Some use one strip, others more than one, and pairs of doors may also have seals at the meeting stiles. That is why the existing groove or the fire rating alone isn't enough to tell you what should be there.

Can intumescent strips be painted over?

This is one of the most common questions because decorators do not always stop at the seal. Current government fire-door guidance tells those carrying out checks to look for intumescent and smoke seals that are damaged or painted over, so paint on a seal should not simply be ignored.

There is an important distinction between the intumescent material and any smoke-control element. Norseal has historically advised that overpainting the intumescent element itself does not necessarily compromise its reaction in a fire. Still, paint on a brush or flexible fin can stop the smoke seal from working as intended. If a smoke-control element has been painted over and can no longer make effective contact, it will need attention.

If you have any doubt about a painted seal, identify the product and check the manufacturer's information rather than scraping paint away and risking further damage.

What should I do if an intumescent strip is damaged?

A strip that is split, badly scored, loose or coming away from its groove should be investigated. Damage is particularly common around ironmongery, where seals may have been cut back during later alterations or caught when locks, hinges and other hardware have been replaced.

Do not assume you can patch a small piece with any intumescent material to hand. The seal forms part of the fire door arrangement, so any repair or replacement needs to maintain the specification supported by the door's evidence.

What if the intumescent strip is missing?

A missing seal may require a bit of detective work. First establish whether an intumescent seal should be present in that position. On an identifiable fire door or doorset, the manufacturer's information, certification, fire door schedule or other records may show the required seal arrangement.

If a section is clearly missing from an otherwise continuous seal, do not leave an open gap. But replacing it is not simply a matter of measuring the groove and ordering a strip of the same width. The material and configuration matter, as do the dimensions.

Where the original specification cannot be established, seek competent advice rather than guessing what was there.

Can a loose intumescent strip be stuck back in?

If a seal has started to come away from its groove, first find out why. The adhesive may have failed, the groove may be damaged, or the seal itself may have deteriorated.

Whether it can be refixed will depend on the product and its condition. If the strip is damaged, distorted or no longer fits securely, replacement may be the better option. Follow the seal manufacturer's fitting instructions rather than reaching automatically for a general-purpose adhesive.

What if the smoke seal brush or fin is damaged?

The smoke-control part of a combined seal needs to make effective contact when the door is closed. A brush clogged with paint or a fin that is torn, flattened or missing may no longer restrict cold smoke as intended.

This can be easy to miss because the intumescent carrier may still look perfectly sound. If the smoke element is damaged, you may need to replace the complete combined seal, depending on the product design.

Can you replace intumescent strips on a fire door?

Yes, you can replace fire door seals, but the replacement must be appropriate for the door. Matching only the width and depth of the old strip is not enough.

Different intumescent materials can expand at different temperatures and generate different pressures. Use the door or doorset evidence to establish the correct material, dimensions, number of seals and position wherever that information is available. If you cannot identify the original seal, get technical advice before choosing an alternative.

Can I replace a brush smoke seal with a fin seal?

Not automatically. A fin seal may offer advantages such as lower friction, easier cleaning and better acoustic containment, but changing the seal on a fire-resisting doorset still needs to be supported by the relevant evidence.

If an existing fire door needs additional smoke protection, a retrofit smoke seal may be an option. These can be fitted to the doorstop without removing or routing the door, making them useful where the existing intumescent seals can remain in place.

Why do fire door seals get damaged?

A surprising amount of damage happens after to the door after installation. Redecoration can cover smoke seals with paint; replacement ironmongery can leave sections cut away; seals can be pulled loose during maintenance; and repeated use can damage exposed brushes or fins.

That is one reason fire door checks need to look at the seals as well as the door leaf, closer and gaps. A door can look sound at first glance, but a small change to its sealing system can alter the original arrangement.

Not sure whether a fire door seal needs replacing?

If you have found a painted, damaged, loose or missing seal, start by identifying the door and the sealing system that should be fitted. Norseal's technical team can help you make sense of the available information and find a suitable replacement or remedial sealing solution.

FAQs about damaged and missing intumescent strips

Can you paint over intumescent strips?

Check paint on a fire door seal rather than ignore it. Paint mustn't clog or restrict a brush or flexible fin used for smoke control. Check the seal manufacturer's guidance before cleaning, repairing or replacing it.

Does paint stop an intumescent strip working?

Not necessarily, but it depends on the seal. Paint can seriously affect the smoke-control brush or fin on a combined seal. If you cannot identify the product or its condition, seek technical advice rather than assuming it is unaffected.

Do damaged intumescent strips need replacing?

A split, loose, badly scored or incomplete strip should be investigated. If replacement is needed, use a seal that matches the specification supported by the fire door's evidence rather than choosing by size alone.

What should I do if an intumescent strip is missing?

First, establish what seal the fire door is supposed to have. If a required section is missing, replace it with the correct material and configuration; don't rely only on groove width to choose a product.

Can I glue a loose intumescent strip back in?

Check the product instructions first. A loose strip may indicate failed adhesive, groove damage, or seal deterioration. Do not use an arbitrary adhesive if the manufacturer specifies a particular fixing method.

Can intumescent strips be replaced?

Yes. The replacement should match the fire door specification for material, size, position, and configuration, where that information is available.

Can I replace an intumescent strip with a different brand?

Do not assume that same-size strips are interchangeable. Intumescent materials can behave differently in a fire, so check the door evidence before substituting another product.

What happens if a smoke seal brush is painted?

Paint can clog the brush and prevent it from making effective contact around the door. A painted or damaged smoke-control element may need replacing.

How do I know if a fire door seal needs replacing?

Look for missing sections, splits, loose strips, heavy paint, damaged brushes or fins and gaps in the sealing line. If you are unsure whether the seal is still suitable, identify the door and seek competent technical advice.