By this stage, the door should already be hung, aligned, fitted with its ironmongery and checked for the correct gaps.
Now it’s time to fit the intumescent and smoke seals.
This sounds like a straightforward job.
In reality, there are quite a few things that can make fitting seals properly much easier — or turn it into a complete nightmare.
I’ve been fitting these seals for years, and I’ve definitely developed my own preferences and ways of doing things.
But there is one thing I always keep coming back to:
The manufacturer’s specification and the tested doorset arrangement come first.
The seal type, size, position and configuration need to be suitable for that particular doorset. BWF guidance also stresses that the correct seals must be compatible with the door’s certification and installation requirements.
Check What Seal the Door Actually Requires
Before I start cutting anything, I want to know exactly what I’m fitting.
Don’t just look at an old seal and assume that’s what should go back in.
The appropriate seal needs to be established from the door manufacturer’s information and the supporting fire-door evidence.
That includes things such as:
- The size of the intumescent seal
- Whether it is fire-only or combined fire and smoke
- Whether it has a brush, fin or other flexible element
- Where it is supposed to be positioned
- Whether it is fitted into the frame or door leaf
- Whether the arrangement is continuous or interrupted around ironmongery
BWF states that intumescent seals must be used as recommended by the door manufacturer, and manufacturers such as Pyroplex likewise instruct installers to select the seal using the relevant door test evidence.
So this isn’t the time to think:
“I’ve got a few lengths of seal in the van. That’ll do.”
It might not.
I Fit the Head First
When I’m fitting the seals, I always start with the head.
The reason is simple.
Once I’ve fitted the head, the legs can push up against it.
That means the legs actually help hold the head in position naturally.
It makes the whole thing easier to fit and keeps everything neat.
Obviously, the exact arrangement depends on the doorset.
You might be dealing with an FD30 or FD60 doorset, a single door, a double door or a particular manufacturer’s system.
So the manufacturer’s instructions still determine exactly what goes where.
But as a fitting method, head first, then the legs is how I normally do it.
Straight Cuts and Tight Joints
When I’m cutting seals, I don’t mess around trying to make complicated mitred corners.
I use straight cuts.
Straight cuts all the way.
Then I make sure the joints are tight.
You don’t want to see little 1 mm or 2 mm gaps appearing around the corners, keeps, hinges or other fittings.
Measure properly.
Cut properly.
Get the joint tight.
It sounds obvious, but a badly cut seal can make an otherwise good doorset look like it has been thrown together.
Keep the Seal Groove Clean
Before fitting an adhesive-backed seal, the surface needs to be properly prepared.
If you’ve got dust, dirt, old adhesive, grease or paint sitting in the groove, you’re asking the adhesive to stick to that instead of the actual substrate.
That’s not a good start.
Pyroplex, for example, specifically instructs installers to clean the substrate and remove dust and surface oils, with clean, dry surfaces required for good adhesion.
This is one of those jobs where spending a little time preparing the groove can save you a lot more time later.
Keep the Decorator Out of the Seal Groove
If I can, I always try to get the seals fitted before the decorator starts painting.
Or at the very least, I make sure the painter knows that the seal groove needs to be kept clear.
This can cause a ridiculous amount of extra work.
You can have a perfectly good groove ready for the seal and then someone comes along and puts paint all the way into it.
Once you’ve got several coats of paint in there, the edges of the groove start getting rounded over.
Instead of having a nice, clean groove for the seal to sit in, you’ve now got paint building up around the edges.
Then you try to put the seal in and wonder why it won’t go in properly.
Removing Paint From the Groove Is a Nightmare
I’ve had situations where you can easily waste an hour or so just trying to get paint out of a seal groove.
You’re scraping it.
You’re picking it.
You’re trying to get into the corners without damaging the groove.
And all because someone painted somewhere they shouldn’t have.
It’s one of those jobs where you look at it afterwards and think:
“That could have been avoided in five minutes.”
So if you’re involved in the installation from the beginning, speak to the decorator.
Keep the seal groove clear.
Don’t Confuse Painting the Seal With Painting the Groove
There is an important distinction here.
Some fire-only intumescent seals can tolerate limited overpainting where the manufacturer’s guidance allows it.
But that doesn’t mean you should simply paint everything.
Lorient, for example, states that its plain fire seals can be overpainted within the limits it gives, while specifically stating that smoke-only seals and combined fire-and-smoke seals should not have their flexible smoke elements painted because this can affect their flexibility and performance.
Pyroplex similarly warns that paint can bind smoke seals and make it difficult for them to perform their smoke-sealing function.
So I don’t treat “paint on a seal” as one simple yes-or-no question.
You’ve got to know what type of seal you’re dealing with.
I’ve Learned to Check Before Calling Something a Fail
I remember carrying out a survey on a door where somebody had painted over the intermittent seal strips.
My immediate reaction was:
“That’s a fail.”
The people involved disagreed.
So rather than arguing about it, I decided to find out.
I contacted ASDMA and spoke to an engineer who had actually been involved in the development of intermittent seals.
He explained that the effect of paint on the particular seal arrangement wasn’t as straightforward as I had initially assumed, and that limited over-painting could be acceptable in the circumstances he was discussing.
That actually taught me something.
I’d always assumed that any paint over an intermittent strip automatically meant failure.
It turns out you need to look at the particular seal, its construction and the supporting information rather than automatically applying a blanket rule.
So my advice is simple:
Don’t guess. Check.
Look at the manufacturer’s information and the supporting evidence for the particular doorset.
Cutting the Seal Around Ironmongery
This is where fitting seals by hand can become awkward.
The factory-machined groove is normally much easier because everything has already been cut around the ironmongery.
When you’re doing it by hand, you’ve got to make those cuts yourself.
The awkward areas can include:
- Keeps
- Flush bolts
- Hinges
- Locks
- Other fittings interrupting the seal run
And some are much easier than others.
Cutting Around the Keep
With the keep, because it’s normally around the centre of the door frame, I can approach it from both directions.
I’ll cut the seal from the top and bottom of the keep, notch it around the fitting and slide the two pieces into position.
If necessary, I’ll leave the cut very slightly proud.
Then, once everything is sitting properly, tightening the fixing back up can help give a nice tight finish around the keep.
I’m trying to make the best possible hand-fitted joint.
You’re never going to reproduce a factory-machined groove perfectly with a knife.
So the trick is to think about how you’re going to get the seal into position before you start cutting it.
Flush Bolts Are Different
Flush bolts are normally right at the very top and very bottom of the door.
So I deal with these differently.
Because they’re at the end of the seal run, I don’t need to piece the seal in from both sides.
I can release the flush bolt, fit the seal from one end, slide it into position and then secure the flush bolt again.
That’s much simpler.
Hinges
Hinges are usually fairly straightforward.
Where I’ve got a fitting in the middle of the seal run, I can generally cut the seal and slide the pieces in from the top and bottom.
A double hinge arrangement can be slightly more awkward because you’ve got more to work around.
But again, I want to keep the cuts simple.
Straight cuts. Tight joints.
That’s the basic principle.
Aviation Cutters Make the Job Much Easier
I’ve found aviation cutters much easier for trimming seals by hand.
They’re basically like having a really sharp pair of scissors that you can get into the seal with and trim down accurately.
You can make a controlled cut instead of hacking away at the seal with a knife.
They’re particularly useful when you’re cutting around keeps, hinges and other ironmongery.
You can also get a really clean 90-degree cut.
And that matters.
Especially with brush seals.
Watch What Happens to Brush Strips After Cutting
Brush strips can be a little more problematic.
Once you’ve cut a brush strip, particularly if you’ve created a short section, you’ve changed the way that piece is retained in the groove.
You can find that the strip starts sliding up and down when the door is operated.
I’ve seen this happen quite a few times.
And once it starts moving, it can eventually work its way completely out of the groove.
If I’ve got a short piece that’s moving and the particular seal system allows it, I might use a small amount of an appropriate adhesive, such as Magneta MITR, or a suitable quick-setting two-part adhesive, to help hold it in position.
I’m not using loads of it.
It’s simply there to stop that short piece moving up and down every time the door operates.
But this isn’t something I’d automatically do to every seal.
The manufacturer’s requirements for that particular seal still apply.
The important thing is that the seal stays where you’ve fitted it.
Don’t Let the Seal Pull Itself Out
This is particularly important with fin seals.
I’ve seen seals pull themselves out of the groove when the door is being operated.
If the adhesive hasn’t got a good grip, or the seal isn’t properly retained, the resistance from the door can gradually pull it out.
Once that starts happening, you’ve got another problem.
The seal is now sticking out where it shouldn’t be.
The door gets harder to operate.
The seal gets damaged.
And eventually you can get to the point where the door won’t shut properly at all.
So if a seal keeps coming out, don’t just push it back in and hope for the best.
Find out why.
Brush Seals vs Fin Seals
I’ve been fitting fire-door seals for quite a number of years, and personally I’ve developed a preference for brush seals.
I’m not the biggest fan of fin seals, particularly when you start getting more than one fin.
A single fin isn’t usually as bad, but with double-fin or multiple-fin seals, I’ve found they can create quite a lot of resistance against the door.
They can actually bind the door.
And when they’re new, you can also get a kind of suction effect.
I’ve seen plenty of occasions during installation where the fin seals have been fitted but the handles haven’t yet been put on.
You go to open the door and it can be surprisingly difficult.
Sometimes someone on the other side actually has to push the door open because the new fin seals are gripping so tightly.
That’s something you need to be aware of when you’re installing the door.
New Fin Seals Can Be a Real Pain
The problem can be worse when the seals are brand new.
They haven’t had a chance to settle through normal operation.
With multiple fins, you’re creating several points of contact around the perimeter.
That can produce a lot more drag and, depending on the configuration, a noticeable suction effect as the door moves.
That’s why I particularly like brush seals.
I find they generally give the door a little more freedom to move without creating the same level of resistance.
But I’m talking about my preference and my experience here.
I’m not saying you can simply substitute one seal type for another.
The seal specified for the particular doorset, and the manufacturer’s installation instructions and supporting fire/smoke evidence, have to be followed.
Don’t Blame the Closer Straight Away
This is another reason I don’t immediately start increasing the closer when a newly installed door feels difficult.
First, I want to work out what is actually causing the resistance.
If the door was operating properly before the seals went in and suddenly becomes difficult afterwards, the seals are an obvious thing to investigate.
The closer might be doing exactly what it is supposed to do.
It may simply be fighting against a lot more resistance from the seals.
Find the cause before adjusting the closer.
Double Doors and Seal Arrangements
If you’re actually making or specifying a double doorset, it’s worth thinking about which leaf is going to carry the seal arrangement.
On a typical push-pull pair, I’d generally prefer to put the seal arrangement on the master door where the configuration allows it.
The reason is practical.
The slave door will often have flush bolts at the top and bottom.
That means you’ve immediately got more interruptions in the seal run and more areas where you’re going to have to cut around hardware.
The master door can be much simpler.
You can have your two straightforward runs of seal and, in some configurations, that’s basically it.
That makes the installation much quicker and gives you a cleaner finish.
It’s something I would think about before the doorset is manufactured, rather than waiting until you’re on site trying to work out how you’re going to get the seals around everything.
Obviously, the final arrangement still has to be the one supported by the doorset’s fire and smoke evidence and manufacturer’s specification.
FD60 Double-Seal Arrangements
If I’m making an FD60 double doorset with a double-seal arrangement and I have a choice of how the seals are positioned, I prefer to put the brush seal furthest into the rebate.
The reason is what happens as the master door closes.
At the crossover point, the gap can be very tight — sometimes around 1 mm.
I don’t want the brush seal trying to squeeze through that tightest part of the closing movement.
I’d rather have the door meet the smoother seal first.
As the master door continues to close and the two leaves straighten up, the gap opens out towards around 3 mm.
That’s where I want the brush seal to come into play.
It gives the brush more room to work and, in my experience, creates less resistance as the door closes.
It’s a small detail, but on an FD60 double doorset with a double-seal arrangement, which seal the door meets first can make a noticeable difference to how easily the doors operate.
Obviously, this is a practical preference where the doorset configuration permits it. The manufacturer’s tested arrangement still controls.
Intermittent Seal Grooves
Intermittent seal grooves can make life much easier.
If the groove has been machined specifically around the ironmongery, you can often fit the seal in sections without having to make complicated hand cuts around every fitting.
It gives you a much cleaner finish.
That’s one of the big advantages of having the groove properly machined during manufacture.
You’re not trying to reproduce that machining with a knife on site.
Some manufacturers specifically allow certain seals to be interrupted around ironmongery, but the exact arrangement must come from the relevant door evidence. Pyroplex, for example, specifies interruption arrangements for some of its seal products.
Drop-Down Seals
Another thing I look at, particularly on older buildings, is the drop-down seal.
These can be useful where you’ve got an uneven or slightly bowed floor and need to deal with the gap underneath the door.
You do need to be careful about what the particular drop-down seal is actually designed and tested for, though.
Some are primarily acoustic or smoke-control products, and you shouldn’t assume that an acoustic drop-down seal automatically provides a fire-rated solution.
If the doorset requires a fire-rated or smoke-control threshold arrangement, the drop-down seal needs to be part of an appropriate tested or assessed configuration.
Don’t Just Wind the Drop Seal Down Until It Touches
I’ve seen people adjust drop-down seals so far that they’re trying to create what is effectively an airtight seal underneath the door.
That’s not necessarily what you’re trying to achieve.
A fire door still needs to operate properly.
If you’ve got an old building with an uneven or bowed floor, you might find that the floor is lower in the middle and higher towards the edges.
If you wind the drop seal down too far to follow the lowest point, you can end up with the seal snagging on the higher parts of the floor when you open the door.
Then it doesn’t retract quickly enough.
The seal gets dragged.
And eventually it can start pulling itself apart or even tear away from the door.
The bottom gap still has to comply with the particular doorset requirements.
As general guidance, BWF gives around 8–10 mm for non-smoke conditions and around 3 mm where smoke seals are required, but the door manufacturer’s instructions take priority.
Where an appropriate drop seal is part of the tested arrangement, it can provide the sealing function at the threshold.
The important thing is not to simply wind the mechanism down as far as it will go.
The door has to operate properly.
Check the Drop Seal Over the Whole Floor
This is particularly important in older buildings.
Don’t just close the door once and look at the seal.
Open and close it several times.
Watch what happens as the seal passes across the floor.
If the floor is bowed, the seal may contact one area more heavily than another.
I want the seal to:
- Drop properly when the door closes.
- Make the required contact.
- Retract when the door opens.
- Pass over the floor without excessive drag.
- Stay securely attached.
If you’re having to wind the adjustment right down just to get contact at one particular low point, stop and think about the floor and the particular seal system rather than simply adding more adjustment.
Drop-Down Seal Covers Get Abused
There’s another practical problem with drop-down seals.
The covers get kicked and knocked.
I’ve been to places where people are constantly moving equipment through doors and the bottom of the door gets abused.
I went to one nursing home where virtually every drop-down seal cover had been knocked off within about three months.
They get kicked.
They get hit by equipment.
People move trolleys through them.
They get caught when things are being carried through the doorway.
So when you’re choosing a drop-down seal, I don’t just look at whether it technically does the job.
I look at where it’s going and what it’s going to be subjected to.
I’ve found some designs much better than others for this sort of environment.
That’s my personal experience rather than a universal statement that one particular construction is always better.
But if you’re fitting them in a busy care home, hospital, corridor or similar environment, think about the abuse they’re going to receive before you choose the product.
Shop around.
Look at how they’re constructed, how they’re adjusted, how they’re retained, what gap they can accommodate and, most importantly, whether the particular product is suitable for the doorset.
What If the Seal Groove Is Wrong?
If the groove is badly routed, that’s really a manufacturing problem.
I’ve had occasions over the years where grooves haven’t been right.
And if you’ve ever had to correct a badly routed seal groove by hand, you’ll know exactly what I mean.
It’s a nightmare.
Sometimes you’ve got no choice but to carefully correct it.
But this isn’t something I want to be doing on a new doorset.
The better answer is for the groove to be correctly machined in the first place.
A groove that’s too shallow, too wide or damaged can also create retention problems.
If the seal relies on both compression and adhesive to stay in position and the groove is too wide, you’ve lost part of that mechanical retention.
For example, if the seal is designed around a particular groove width and you’ve effectively made the groove wider, you’re relying much more heavily on the adhesive.
Eventually the seal can start working its way out.
In extreme cases, additional approved securing may be necessary, but this is not something I’d regard as a normal installation method.
The correct groove should be manufactured to the required dimensions in the first place.
Check the Adhesive
Normally I’ll use the manufacturer’s adhesive system if the seal is supplied with adhesive.
I don’t immediately reach for something else.
If the adhesive is properly applied to a clean, suitable surface, it should do what it is intended to do.
If the seal keeps coming away, though, I want to find out why.
It could be:
- A dirty groove
- Paint contamination
- Grease or oil
- Poor preparation
- The wrong temperature
- A damaged substrate
- An unsuitable groove
- Or a problem with the adhesive itself
Manufacturers such as Pyroplex specifically require clean, dry surfaces for good adhesion.
Don’t just keep adding more glue without finding the cause.
The Seal Should Stay Where You Put It
This is probably the simplest way I can describe what I’m looking for.
Once I’ve fitted the seal, I want it to stay there.
It shouldn’t:
- Slide up and down
- Pull out of the groove
- Fold over
- Roll up
- Catch on the door
- Snag against the frame
- Or prevent the door from closing properly
It should sit properly in the groove and work with the door.
Operate the Door Again
Once I’ve fitted the seals, I don’t just look at them and say:
“That’s done.”
I operate the door.
I’ll open it.
I’ll close it.
I’ll do it again.
I’m looking at what the seals are actually doing.
Does the door close properly?
Is anything snagging?
Are the brush or fin seals creating excessive resistance?
Is the closer still closing the door properly?
Has anything moved?
If the door is struggling to close after the seals have been fitted, I don’t immediately turn the closer up.
I’ll check the seals.
I’ll check the gaps.
I’ll check the door alignment.
And then I’ll look at the closer if necessary.
BWF’s installation guidance specifically says the completed door should be checked to make sure the closer shuts the door onto the latch from any position.
Don’t Chase Perfection by Making the Door Hard to Operate
There’s a temptation with seals to think:
“If a little is good, more must be better.”
It isn’t.
You don’t want to wind a drop seal down until it’s dragging across the floor.
You don’t want to fit a fin seal so aggressively that the door struggles to open.
You don’t want a brush seal pulling itself out because it’s being forced through a gap that’s too tight.
And you don’t want to increase the closer just to overcome a problem you’ve created with the seals.
The whole doorset has to work together.
Final Seal Check
Before I move on, I want to check:
- Correct seal type
- Correct seal size
- Correct position
- Clean groove
- Tight joints
- No unnecessary gaps
- Seal properly seated
- No loose sections
- No brush or fin pulling out
- No paint contamination
- No snagging
- Door opens properly
- Door closes properly
- Closer still operates correctly
- Drop-down seal, where fitted, operates correctly
- Seal arrangement matches the manufacturer’s requirements
The seal isn’t just something you push into a groove at the end of the job.
It’s part of the doorset.
BWF describes the fire door as a complete assembly, including the frame, leaf, intumescent and smoke seals and essential hardware.
Don’t Forget What the Seal Is Actually There For
It is easy to get caught up in cutting, fitting and making everything look neat.
But the reason we’re doing all this is because the seals are part of the fire and smoke performance of the doorset.
Intumescent seals expand when exposed to heat and help close the gap between the door and frame.
Smoke seals provide additional protection against the passage of cold smoke.
They aren’t decorative strips.
They’re part of the system.
And the particular seal arrangement needs to match the door’s supporting evidence.
🟧 Professional Installer’s Tip
Think about how the seal is going to work before you start cutting it.
Look at the door.
Look at the ironmongery.
Look at the gap.
Think about how the door is going to move.
Then cut the seal.
A few seconds thinking about it beforehand can save you a lot of messing around afterwards.
And when you’ve finished, operate the door.
Don’t just look at the seal and assume it’s right.
Make sure the whole doorset still works properly.
Continue the Fire Door Installation Series
← Previous: Part 12 – Measuring & Setting Fire Door Gaps
Part 13 – Installing Intumescent & Smoke Seals — You are here
