Once the frame has been prepared, packed and fixed, the next stage is preparing the fire door leaf.

This is a stage I don’t rush.

When you’re going through door after door on a large job, eventually they all start looking like white painted walls. That’s when you have to make sure you are still checking every door properly rather than assuming it is the same as the last one.

Before I start cutting, chiselling, drilling or repairing anything, I want to know exactly what I’ve got in front of me.

The door needs checking for its size, thickness, construction, lippings, factory machining, damage, certification markings and any preparation that needs doing before it is hung.

A fire door is a tested component, so you can’t just treat it like an ordinary joinery door and alter whatever you want. The manufacturer’s certification and installation instructions need to be checked before carrying out alterations.

BS 8214:2026 is the current British Standard for fire-resisting and smoke-control doors and is the standard used as the baseline for this series. The individual door manufacturer’s certification and instructions remain important because they determine what is permitted on that particular door.

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Start by Identifying the Door

Before doing anything, check what door you’ve actually got.

Common metric door sizes you’ll come across include:

• 626 × 2040 mm
• 726 × 2040 mm
• 826 × 2040 mm
• 926 × 2040 mm

You’ll also come across imperial sizes, particularly in older buildings.

One common imperial size is:

762 × 1981 mm – 30″ × 78″

There are different thicknesses and constructions as well.

For a quick check, I use a two-finger rule for a 44 mm door and a three-finger rule for a 54 mm door.

It’s only a quick check though.

If I need to know the actual thickness, I measure it.

There are 60 mm FD90 doors around, although these are rare in the work I see. There are also 35 mm FD30 doors available now, although I haven’t personally come across them in the same way as the more common 44 mm and 54 mm constructions.

The important thing is not to decide what the door is just by looking at it.

Check it.

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Check the Certification Marking

Before you start altering the door, find the certification label, plug or other identification marking.

These are commonly found on the top edge or hinge side, depending on the manufacturer and certification scheme.

The marking is important because it allows the door to be identified and traced back to its certification.

Different manufacturers and certification schemes use different systems, so don’t assume that a particular colour or plug means the same thing on every door.

Check the manufacturer’s information.

And don’t remove the marking.

Don’t plane over it.

Don’t cut through it.

Don’t damage it.

If the area you need to alter could affect the certification marking, stop and check the documentation first.

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Check the Door for Damage

Before I do any work to a door, I want to know what condition it arrived in.

Check both faces and all four edges.

Look for:

• scratches;
• dents;
• gouges;
• damaged veneer;
• damaged laminate;
• chipped corners;
• crushed corners;
• split lippings;
• exposed core;
• damaged edges;
• transport damage;
• poor factory finishing;
• previous repairs.

A door can look absolutely fine from a few feet away and then you get close and find a crushed corner or damaged lipping.

This is particularly important with remedial work because you don’t want to start working on a door and then later have somebody tell you that you caused damage that was already there.

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Check the Lippings

The lippings need a proper inspection.

As a general construction, I’ve commonly seen approximately:

• 9 mm lippings on FD30 doors
• 12 mm lippings on FD60 doors

But don’t look at that and think you’ve got 9 or 12 mm available to remove.

The amount that can actually be removed depends on the particular manufacturer’s certification.

I don’t take much off doors anyway.

With the way I install them, I very rarely need to remove much material.

You also need to remember that the hardware is being fixed into the door.

Take too much off and you can start getting into areas where your hinges, locks and other hardware need to be properly fixed.

If you’re taking a lot off the door just to make it fit, something else may be wrong.

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Check for Split or Damaged Lippings

If a lipping is split or damaged, don’t automatically assume the door needs throwing away.

I’ve repaired and replaced lippings numerous times, but this is only something to do where the particular door’s certification allows it.

My usual method is to get the damaged area straight with a sharp chisel.

I’ll then make a straight piece of timber to fit the damaged section, glue it in and clamp it.

When clamping, I put other pieces of timber between the clamps and the door so I don’t mark the door.

I also wipe away the excess glue.

You don’t want the pieces of timber you’re using to protect the door becoming glued to it.

Once the repair has set, I’ll saw the excess timber off, leaving it slightly proud.

Then I’ll use a sharp chisel to remove the last few millimetres until it matches the original lipping.

That’s where you need to take your time.

You’re taking tiny amounts off until the repair follows the original shape.

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Check the Door is the Correct Hand

Before you start preparing hinges or hardware, make sure you’ve established which way the door is handed.

You need to know:

• which is the hinge side;
• which is the latch side;
• which way the door is going to open;
• where the hardware is going.

This becomes particularly important when the door has factory machining already carried out.

You don’t want to start correcting or machining the wrong edge because you’ve assumed the handing.

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Check the Door is Square and Straight

Before you start taking material off, check the leaf itself.

A door can be the correct overall size but still have problems with its shape.

Look along the door and check for obvious:

• bowing;
• twisting;
• distortion;
• out-of-square conditions.

If the leaf itself is badly distorted, you don’t want to start altering the frame or cutting the door to compensate for it without understanding what you’re dealing with.

The aim is to prepare the door — not hide a defective door by altering everything around it.

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Check for Previous Alterations

Particularly on replacement or remedial work, don’t assume the door is untouched.

Look for signs that somebody has already:

• trimmed it;
• altered a hinge recess;
• enlarged a lock preparation;
• repaired a lipping;
• altered the bottom edge;
• fitted and removed hardware;
• carried out other machining.

You need to know what has already been done before deciding what you can do next.

A door that has already been heavily altered may have less scope for further work than a new, untouched door.

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Check the Factory Machining

I always check factory machining before I start fitting hardware.

The factory isn’t infallible.

I’ve seen hinge recesses that haven’t been made deep enough.

If the certified preparation allows the correction, get your chisel out and make the recess right.

There isn’t much point trying to force a hinge into a recess that hasn’t been cut deep enough.

But there is an important difference between correcting a factory preparation and creating a new alteration that isn’t covered by the certification.

The same applies to lock and latch preparations.

Check what has been provided before you start making your own holes.

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Check Where the Door Can Be Machined

This is particularly important with different door constructions.

Some doors have specific areas intended for hardware preparation.

You can’t just assume that because there is timber in an area, it is suitable for whatever you’re about to put in it.

Some constructions have solid timber in particular areas and different construction elsewhere.

The manufacturer’s information should tell you where the permitted machining is.

This applies to:

• hinges;
• locks;
• latches;
• closers;
• other hardware.

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Preparing for Hinges

The actual hanging and hinge installation comes in the next part, but the leaf needs to be ready for it.

Check that:

• the hinge positions are correct;
• the recesses are the correct depth;
• the hinge fits properly into the recess;
• the correct hinges have been selected;
• any required intumescent hinge protection is available.

Don’t assume a factory hinge recess is automatically perfect.

I’ve come across plenty where they haven’t been deep enough.

If it needs correcting and the certification permits the work, correct it before you’re standing there trying to hang a heavy door into a bad recess.

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Be Careful When Drilling

When you’re preparing the door for locks, latches, hinges or other permitted hardware, take care with the drill.

Some drill bits can split the timber when they enter.

I’ve found auger bits with the pilot screw can be quite aggressive because the screw pulls the bit into the timber.

In my experience, speed bits are less likely to split the timber in the same way.

The important thing is to keep control of the drill.

Don’t let the bit drag itself into the door.

Don’t just put the drill on full power and hope for the best.

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Check the Glazing

If the door has glazing, inspect the factory-prepared glazing aperture.

Check:

• the glass;
• beads;
• seals;
• fixings;
• the condition of the aperture;
• damage around the aperture;
• the finish around fixing holes.

One thing I’ve seen is holes around glazing fixings being left visible because they haven’t been properly waxed or finished over.

That’s a factory finishing issue worth spotting before the door is installed.

What you don’t do is simply cut or enlarge a fire-door glazing aperture because you think it needs changing.

Glazing apertures and the glazing system need to be covered by the appropriate certification.

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Check the Closer Preparation

Some better-quality doors have solid construction through the head to allow closer fixings.

This is something worth knowing before you’re fitting a closer.

Don’t assume that because you can physically put a screw into the door, that the door has been designed or certified for that fixing arrangement.

Check the manufacturer’s instructions and certification.

The same principle applies to all the hardware.

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Check the Bottom of the Door

The bottom edge needs particular attention.

First check the condition of the bottom lipping and make sure there hasn’t already been damage or previous trimming.

Then look at what the door is actually going to sit over.

Think about:

• the finished floor;
• tiles;
• carpet;
• vinyl;
• thresholds;
• uneven floors;
• changes in floor level;
• the required clearance beneath the door.

Don’t just cut the door because the floor looks high.

The required clearance depends on the particular door and its certification.

And this is also where you need to think about whether the door is going to have a drop-down seal.

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Drop-Down Seals

There are lots of different drop-down seal systems available.

Some doors have them factory fitted.

Some systems are fitted internally into the bottom of the door and require the correct routed preparation.

Others are face fitted to the door.

So this is something you need to know about before the door is hung.

If you’re fitting a concealed drop-down seal, the preparation may require routing into the bottom of the door.

You don’t want to have the door hanging, everything aligned and then realise you’ve got to take it all back down because you’ve forgotten the seal preparation.

There are plenty of manufacturers making these systems and I’ve got manufacturers I personally prefer because of what I’ve seen from them over the years.

But there are lots of different types, so look at what’s actually suitable for the job rather than assuming one system is right for everything.

I’ve had to go back to numerous jobs over the years because face-fitted drop-down seals have been knocked off.

I’ve seen the covers knocked off.

I’ve seen them badly fitted.

I’ve seen the rubber pulled out.

And once the seal has been damaged or pulled out, you’ve got another remedial job.

A drop-down seal is there to do a job, but it also needs to survive normal use.

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Cutting the Door Down

If the door needs trimming, don’t just reach for the saw.

First check that trimming is actually permitted and how much the manufacturer allows you to remove.

Don’t assume that because you’ve got a 9 mm or 12 mm lipping, you can simply remove that amount.

If trimming is permitted, take the minimum necessary.

If you’re cutting from the bottom, pay attention to how you make the cut.

The saw can spelch the timber or facing as it exits the far side.

I prefer to make a shallow scoring cut first.

Then progressively cut deeper.

This gives you more control and reduces the chance of the saw breaking out the other side and damaging the door.

The same applies when using a router.

Be careful as the cutter exits the work.

That’s where you can suddenly take a chunk out of the facing if you aren’t careful.

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Finish Any Cut or Planed Edge

Once you’ve cut or planed an edge, don’t leave it rough.

Lightly sand it down.

I also like to put a small arris on the bottom edge.

A freshly cut edge can be razor sharp.

You’re not trying to remove a load more material — you’re simply cleaning it up and taking that sharp corner off.

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Protect the Bottom Edge

If you’ve exposed fresh material by cutting the door, the edge needs to be protected in accordance with the manufacturer’s requirements and certification.

This is particularly important where doors are installed over tiled floors that are regularly cleaned with mops.

I’ve seen lower-quality chipwood/chipboard-core doors absorb water at the bottom.

Once the core starts taking in water, it can swell.

Then you’ve got a door that starts catching and you’re back doing remedial work.

And it doesn’t necessarily have to be a door that has been cut.

A factory bottom edge can still suffer from repeated water exposure.

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Minor Face and Veneer Repairs

Not every damaged-looking door needs to go away for a complete refinish.

For minor cosmetic damage, I carry Liberon repair sticks in every colour.

I’ve also got specialist grain-drawing pens in different wood shades, repair lacquer and I’ve got experience with French polishing as well.

I’ve taught others how to do it too.

A small scratch in a veneer can sometimes be repaired on site rather than waiting for a French polisher.

But there is a big difference between a cosmetic repair and damage to the actual construction of the fire door.

If you’ve damaged the core, lipping or another important part of the construction, you need to check whether an approved repair is possible.

I’ll cover the more detailed veneer and French polishing work separately rather than filling this article with it.

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Final Check Before the Door Goes in the Frame

Before I hang the door, I want to know that the leaf is ready.

I’ll check:

• the size;
• thickness;
• handing;
• lippings;
• top edge;
• bottom edge;
• both faces;
• corners;
• certification marking;
• hinge preparations;
• lock preparation;
• closer preparation where applicable;
• glazing;
• factory machining;
• previous alterations;
• damage;
• trimming;
• drop-down seal requirements;
• any repairs.

If something needs doing to the leaf, now is the time to do it.

You don’t want to hang a heavy fire door and then realise you’ve forgotten something that means you’ve got to take it down again.

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Preparing the Door Properly

For me, preparing the fire door leaf is about getting everything ready before the door goes anywhere near the frame.

Check it.

Measure it.

Look at the construction.

Look for damage.

Check the certification.

Check the factory machining.

Work out what hardware is going into it.

Think about the bottom clearance.

Think about whether it needs a drop-down seal.

Then, and only then, start making the alterations that are actually permitted.

I’ve always found that the more preparation you do before hanging a door, the easier the actual hanging job becomes.

You’re not trying to make the door fit by attacking it with a plane or chisel.

You’re preparing a certified door leaf so that it can be hung correctly and work properly as part of the complete fire door assembly.

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Key Takeaways

• Check the door before starting any work.
• Confirm the size, thickness and handing.
• Check the lippings and all four edges.
• Check both faces for damage.
• Check for crushed corners and split lippings.
• Look for previous alterations and repairs.
• Check the certification label or plug.
• Never remove or damage certification markings.
• Check factory hinge and lock preparations.
• Make sure any machining is permitted by the door’s certification.
• Check glazing and factory finishing.
• Don’t cut or enlarge glazing apertures unless the work is being carried out within the appropriate certified process.
• Check the bottom edge and finished floor conditions.
• Establish whether a drop-down seal is required.
• Check whether the drop-down seal is factory fitted, internally routed or face fitted.
• If routing is required, do it as part of the preparation before hanging the door.
• If trimming is permitted, remove only what is necessary.
• Use controlled scoring cuts to reduce spelching.
• Lightly sand and arris freshly cut or planed edges.
• Protect exposed edges as required by the manufacturer.
• Investigate water damage rather than simply removing the swollen material.
• Only repair or replace lippings where the certification permits it.
• Minor cosmetic damage can sometimes be repaired on site.
• Always check the certification before altering the door.

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Continue the Fire Door Installation Series

Part 5 – Installing a Fire Door Frame

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Part 6 – Preparing the Fire Door Leaf

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Part 7 – Hanging & Aligning the Fire Door

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