Once the door has been correctly aligned in the frame, the next stage is to fit the stop lath.
This is one of those jobs that looks simple, but there is actually quite a bit of skill in getting it right.
One of the advantages of fitting the stop lath at this stage is that the door is already positioned in the frame. You can therefore fit the stop to suit the actual door rather than trying to make the door fit a stop that has already been fixed.
You can get away with a lot more with a stop lath than you can with a door frame because you have some ability to position it to deal with small discrepancies in the finished installation.
That doesn’t mean using the stop to hide a badly installed frame. The stop lath forms part of the doorset and its size, material, position and fixing method must be compatible with the particular fire-rated system and its manufacturer’s requirements.
Stop Lath Sizes
As a rough guide, a stop lath can be around 15 mm × 32 mm.
This gives you approximately a 15 mm stop against the door.
You will see wider stop laths as well, although I don’t see them as often.
The actual size needs to be checked against the particular doorset.
The same applies to the material.
As a practical guide, I have generally seen hardwood laths used with FD60 doors, with MDF or softwood used for FD30, but this isn’t something I would apply blindly to every doorset.
Always check what the manufacturer specifies for the particular door.
The stop lath is part of the rated system, so the material, size and profile are important.
Fitting the Stop to the Door
As a joiner, I was taught to hold the door level with the frame while fitting the stop.
Ideally, this is a two-person job.
You have someone on the other side holding the door flush with the frame while you work from the opposite side fitting the stop.
This gives you a proper reference to work from.
You’re not guessing where the stop needs to go.
The door is already there, so use the door as your datum.
My 1 mm Packer Method
I was taught to use a 1 mm packer between the door and the stop lath.
The idea is to leave a small amount of clearance so the door doesn’t bind against the stop when it opens and closes.
I’ve used this method for years.
However, there is something I have learned from experience.
If the door is already finished, the 1 mm method can work well where it is appropriate for the particular doorset.
If the doorset still needs to be painted or finished, I have found on numerous occasions that 1 mm isn’t enough.
The finishing layer can effectively take that clearance away.
You can leave a door working perfectly, the painter comes along, adds the finishing coats and suddenly the door is binding.
Where the doorset permits it, I use a 2 mm packer when there is still a finishing trade to come, giving that extra allowance for the finish.
The important point is to check the specified clearances for the actual doorset rather than treating 1 mm or 2 mm as a universal fire-door requirement.
🟧 PRO TIP – THINK ABOUT THE FINISHED DOOR
If the door still needs painting, don’t just think about how it fits today.
Think about what it will be like after the finishing coats have been applied.
I’ve seen doors that work perfectly before painting start binding afterwards because the finishing layer has used up the available clearance.
Start With the Head
I always start with the head of the stop lath.
You need to cut it to fit between the fixed head details.
Use your appropriate packer and fix either end first.
This is a general rule in joinery that I use all the time.
It doesn’t matter what you’re fixing — fix either end first and then work the rest of the line into position.
Once both ends are fixed, you can work the rest of the stop into line.
🟧 PRO TIP – FIX BOTH ENDS FIRST
Don’t start at one end and work your way along a long piece.
Fix either end first, establish your line and then work the rest of the length into position.
I use the same principle when fitting frames and other long pieces of joinery.
It gives you much more control over the finished line.
Fix the Head First
With the door held correctly:
- Position the head stop.
- Put your packer between the door and stop.
- Fix one end.
- Fix the other end.
- Check the line.
- Work the remaining fixings between the two ends.
Once the head is correct, move onto the legs.
Work Down the Jambs
Fix the top of the leg first.
Then work down each jamb.
Keep using your packer as you go so the relationship between the door and stop remains consistent.
If you have someone helping you, they can continue holding the door level and flush with the frame while you fix the stop.
That makes it much easier to maintain the correct position.
Working on Your Own
You don’t always have someone available to hold the door.
If I’m fitting numerous doors on the same job, particularly where the frames and doors are consistent, I use a quicker method.
I make what we call a traveller.
A traveller is simply an offcut of stop lath that I have worked out and marked to give me the required set size.
Once you’ve made one, you can use it repeatedly instead of getting the tape measure out every time.
Making a Traveller
The principle is straightforward.
You work out the required door width and the clearance you need, then make an offcut to represent that dimension.
For example, if you’re working with consistent doorsets, you can have a traveller made specifically for them.
On some jobs I have two travellers:
One for FD60 and one for FD30.
I mark them clearly so I know which is which.
This is particularly useful when you’re doing numerous doors and don’t want to keep calculating or measuring the same thing.
🟧 PRO TIP – MAKE YOURSELF A TRAVELLER
If you’re doing lots of identical doors, make yourself a traveller from an offcut of stop lath.
Work out the correct dimension once, mark it clearly and use it as your gauge.
I’ve used separate travellers for FD60 and FD30 doors and marked them accordingly.
Measure once, make your traveller and repeat.
Use the Traveller From the Other Side
I use the traveller from the back, non-hanging side of the door.
Offer the stop lath up to the frame with the traveller held against the other side.
This gives you the set size without needing somebody to stand there holding the door for you.
If you can offer the piece for the head up to the frame, you can mark it directly across and cut it.
Then use the traveller to offset the head position down the legs.
The traveller gives you the same reference for each side.
🟧 PRO TIP – MARK IT FROM THE ACTUAL JOB
If you can offer the stop lath directly into position, mark it from the actual frame rather than reaching for the tape measure.
Offer it up, mark it and cut it.
Then use the traveller to transfer the same set-out down the legs.
There is no point measuring something three times when the actual component can give you the dimension.
Why This Is Useful on Repetitive Jobs
When you’re fitting one door, the time saving might not seem significant.
When you’re fitting dozens of doors with the same dimensions, it becomes much more useful.
If the doors and frames are consistent, the traveller gives you a repeatable physical reference.
You aren’t constantly measuring the same dimension.
You establish it once and then reproduce it.
That’s one of those little joinery tricks that can make a big difference over a large job.
The Stop Can Conceal Fixings
Another advantage of the stop lath is that it can sometimes be used to conceal frame fixings.
Where the approved doorset construction allows it, you can position fixings behind the stop so they aren’t visible once the stop has been installed.
This gives you a much cleaner finished appearance.
But don’t use the stop as an excuse to put fixings wherever you want.
The fixing arrangement still needs to comply with the manufacturer’s approved installation method.
🟧 PRO TIP – USE THE STOP TO HIDE FIXINGS
Where the approved construction allows it, the stop lath can give you a neat way of concealing frame fixings.
It can make a big difference to the finished appearance.
But hiding a fixing doesn’t make an incorrect fixing arrangement acceptable.
Check the manufacturer’s requirements first.
Glue or Mechanical Fixing?
This is something I have some concerns about because what I was taught and what I increasingly see on site aren’t always the same.
I was taught to glue the stop lath into position.
I have also seen this specified in manufacturer installation guides.
But I’m seeing more stop laths being installed without glue, heavily nailed instead and then held in place with caulk once the doorset has been decorated.
I can understand why people do it.
From a maintenance point of view, an unglued stop can be much easier to remove.
If a glued stop needs to come off, the lath can come out in pieces and you can be left with timber and adhesive stuck to the frame.
That then needs scraping away before the replacement stop can be fitted.
If the stop isn’t glued, it can potentially be removed and reapplied much more easily.
But Check the Manufacturer’s Instructions
This is where I would be very careful.
You cannot simply choose the easier maintenance option if it goes against the approved doorset installation method.
Some manufacturers specify adhesive together with mechanical fixing.
Others have their own approved arrangements.
The stop is part of the fire-rated construction, so the method used to attach it needs to be the method permitted for that particular doorset.
If the manufacturer’s instructions say glue it and mechanically fix it, that’s what you do.
🟧 PRO TIP – DON’T CHANGE THE APPROVED METHOD
I’ve seen unglued stop laths that are much easier to remove for maintenance.
From a joiner’s point of view, I can see the attraction.
But if the manufacturer specifies adhesive and mechanical fixing, you use it.
Future maintenance convenience doesn’t override the approved fire-door installation method.
Always check first.
Don’t Use the Stop to Hide a Bad Frame
There is a difference between using the stop lath to deal with a small discrepancy and using it to hide a badly installed frame.
The stop gives you some flexibility because you’re fitting it to a door that is already in position.
That’s useful.
But it isn’t unlimited.
If the frame is badly twisted, the door is incorrectly positioned or you cannot achieve the required clearances, don’t just move the stop until the problem disappears.
Go back and find the actual cause.
The stop lath forms part of the doorset.
It needs to be correctly positioned rather than simply used as a cover-up.
Check Everything Again
Once the stop lath is fitted, operate the door again.
Open it.
Close it.
Check that it isn’t binding.
Check the relationship between the door and stop.
Check the head and both jambs.
Check that the stop is straight.
Check that no fixing is interfering with the door.
Check that the door is still sitting correctly in the frame.
This is another reason why I like fitting the stop after the door has been positioned.
You can see exactly what you’ve achieved.
Stop Lath Checklist
Before moving onto the next stage, check:
Stop lath
- Correct material for the doorset.
- Correct dimensions.
- Correct profile.
- Correct position.
- Straight and properly aligned.
Door relationship
- Door remains correctly positioned.
- Correct clearance for the particular doorset.
- No binding.
- Door opens and closes freely.
- Door isn’t being forced against the stop.
Fixings
- Correct fixing method.
- Adhesive used where required.
- Mechanical fixings used where required.
- Fixings correctly positioned.
- Concealed fixings only where permitted.
Finishing
- Allowance for finishing considered where appropriate.
- Stop doesn’t interfere with the door operation.
- Stop is secure.
- No damaged edges or unnecessary gaps.
Key Takeaways
- Fit the stop lath after the door has been correctly aligned.
- The stop gives you some ability to accommodate small discrepancies in the finished installation.
- Don’t use it to hide a fundamentally incorrect frame installation.
- Stop-lath material, size and profile need to comply with the particular doorset.
- A stop lath can conceal fixings where the approved construction allows it.
- Hold the door correctly while positioning the stop.
- Start with the head.
- Fix both ends first and work the rest of the line into position.
- Work down each jamb from the top.
- A traveller can make repeated installations much quicker.
- Separate travellers can be made for different doorset types.
- Think about the finished door when allowing for painting and finishing.
- Don’t assume that 1 mm or 2 mm is a universal fire-door requirement.
- Check the manufacturer’s requirements for adhesive and mechanical fixing.
- Always operate and check the door again after fitting the stop.
Continue the Fire Door Installation Series
Part 7 – Aligning the Door in the Frame
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Part 8 – Fitting the Stop Lath
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Part 9 – Installing Fire Door Hinges
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Important
This guide is based on practical installation experience and is intended to explain the techniques and problems encountered when installing fire doors.
Fire doorsets are tested and assessed as complete systems. Always follow the installation instructions supplied for the particular doorset, manufacturer, hardware, materials and supporting certification, test or assessment evidence.
Where the manufacturer’s documented installation method differs from a general technique described here, the manufacturer’s approved method takes priority.
