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I have a set of 1927 french doors that are 18" wide and have a built-in astragal -- measuring ~7/8" wide and ~1/4" deep -- on both doors. The astragal narrows to about a 1/4" where the locks used to be, allowing room for the former lock.

I'm restoring the doors and I'd like to add a lockset to the active door (passive door is secured with slide bolts). I'm wondering if I should try and add a modern mortise lock to the door by removing whatever filler is in the old hole or attempt to add a modern deadbolt and knob in.

My concerns with using a modern deadblot/knob is that the distance between the base plate and the strike plate will be too great and the knob's latch won't be long enough to securely catch.

Here's a picture of the door edges. The original strike plate is still there, but the hole where the mortise lock used to be has been filled.

How would you proceed?

As a side note, I've considered replacing the doors with a new set, but no one stocks french doors in this size. When installers come out, they all suggest adding a full size entry door, but a full size door would open too far into the room and be awkward in the space. Also, I just like the look of the smaller doors. The only other replacement option I've thought of would be to use a pair of 18" sidelights and turn them into french doors.

Door Edge Profile

  • Are the slide bolts on the inactive leaf manual or automatic? Also, what space does this door serve? I ask because the current configuration may not meet any codes with regards to egress, escape, or accessibility, especially with the inactive leaf "bolted down" , so to speak. – ThreePhaseEel Jul 25 at 21:47
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    The door serves a small deck off the living room. The slides are manual and are currently installed on what will be the active door (they'll move to the inactive door once a suitable lock is found). A previous owner had the doors sealed shut and this was the best option for me when I managed to get the doors to open several years ago. I would use automatic bolts if I can find a set that will work. – Anthony Jul 25 at 21:56
  • Are you willing to spend a bit of money on this? The "latch a door leaf to another door leaf" thing isn't at all an unheard-of function, but most of the hardware made for it is commercial stuff that isn't exactly cheap (it's more commonly found on fire doors to mechanical spaces, where the inactive leaf can be opened to provide additional width beyond Code egress mandates so that stuff can be brought in/out) – ThreePhaseEel Jul 25 at 22:01
  • Also, how thick are the door leaves at their edges? – ThreePhaseEel Jul 25 at 22:02
  • Yeah, most automatic bolts I've found are intended for use in metal doors. I haven't seen anything for wood doors so I'm not exactly thinking it's a viable option, but I will keep looking. The doors are 1 7/8" wide, with the astragals being ~15/16" at their wide point and ~1/4" where the plates are. – Anthony Jul 25 at 22:36
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Those types of latches for had specific shapes to follow the door edge profiles. You may be able to find a new latch that will work, but I would suggest shopping for an antique latchset that will suit your needs and have it reconditioned by a locksmith.

After that is accomplished, then cut out what is needed to get the new or reconditioned latchset to work. Don't just remove what was filled in, although it may be needed anyway, but some filler may be able to remain, since the new lock may have different cutouts needed. Then again, in making the new mortices (cutouts) the filler may fall out anyway. Just as well, if it does, it can be reset properly and more permanently.

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  • Would an antique latch be able to use a modern keyed tumbler? When looking for vintage mortise locks, most seem to use a skeleton key, but maybe they are intended for interior use. – Anthony Jul 25 at 22:38
  • I believe there are types out there that take the cylinder type key ways – Jack Jul 25 at 22:40
  • I did a brief search online for the lock set, but did not find any results that were satisfactory. I know they are out there, or should be, since I have seen them around while I was still on the east coast... – Jack Jul 25 at 23:13
  • Do you know what the mortise lock that followed the profile might be called? Extruded? Protruded? I can envision a mortise lock with an extruded section that fits into the strike plate, but just not sure what it would be called. – Anthony Jul 25 at 23:42
  • That is were I was having trouble, coming up with keywords for searching. Even using pictures only was of no help. But I did not spend a lot of time on it. I did think it would have revealed something in the little while i searched.... – Jack Jul 25 at 23:55
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You'll want a pair of automatic flush bolts if you want this opening to have any semblance of Code-compliance

The problem you have here is that not only does the French door setup you have require funny latchset hardware to fit the existing door, it doesn't provide enough clear opening width (equivalent of a 24" leaf is necessary) to meet Code requirements unless both leaves are operable. As a result, you'll need to have something more sophisticated than a simple set of surface bolts on the inactive leaf; in particular, you need a pair of automatic flush bolts that latch the inactive leaf when the active leaf is closed and unlatch it when the active leaf is open. Since this hardware is designed for fire door service, it's not a common or cheap item, but versions for 1¾" minimum solid wood doors are available, such as the Ives FB41P or the Rockwood 2942.

Also, may also have difficulty with the latchbolt setup depending on what you use; it'll need to spring-in if closed into so the inactive leaf doesn't hang on the latchbolt if closed into a closed active leaf. If you didn't do that, you'd wind up needing a coordinator to hold the inactive leaf open while the active leaf closed, which is an added expense (and thing that can break).

The other alternative would be to make these both active leaves with vertical rod latching hardware, but that would require some hackery as most vertical rods are found on panic hardware (crash bars), which are far wider than this application calls for, and can't reasonably be shortened atop going on the push side of the door, while not being lockable from that side. A pushpad type of device could be used here, but I'm not sure if surface vertical rod versions of those are made.

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  • Now that I've been researching this for a bit, similar hardware is available but not easily procured. (rabbeted mortise locks are still fairly common in the UK, Australia, and New Zealand). If the house was built with these doors, why do they have to become code compliant? The doors are staying the same, I'm just replacing the locks with a modern counterpart. I think I've seen this referred to as "like for like". If I was adding a door to the structure, then I could see why code compliance is important, but is it necessary when simply repairing something already in place? – Anthony Jul 29 at 16:05

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