Introduction #
An apartment unit entry door is not a pre-hung install. On most multifamily jobs the frame is a hollow metal frame (a steel jamb, not wood), set into the rough opening by the framers well before drywall goes up. A lot of times our job is the slab only, and another trade handles the frame; whether we do both the frame and the slab or just the slab depends on the GC, so confirm the scope for each job. This guide covers the slab side of that work: fit a new slab (the door panel itself, without a frame) to that existing frame, mortise the hinges to match it, and add a sweep at the bottom for sound and draft control between the unit and the corridor.
Unlike a pre-hung unit, you do not control the frame here. It is already set, plumb or not, square or not, and your job is to make the new slab work with what is actually there. That is why this is Advanced work: you are fitting to an existing opening instead of building the margin from scratch, and apartment entry slabs are heavier commercial-grade doors that often carry factory hardware cutouts that have to line up exactly with the hinge mortises already cut into the frame.
Apartment entry doors are also one of the few interior doors that can go in before drywall. Everywhere else in residential work, wood-cased pre-hung doors wait until drywall is finished. A hollow metal frame at a unit entry is the exception, since the framer or the door supplier sets that frame at rough construction. That frame goes in before drywall; the slab this guide covers goes in toward the end of the job, well after the frame has been standing.
Before You Begin #
Prerequisites #
- The hollow metal frame is installed, plumb, and secure in the rough opening (framer or supplier work, not ours)
- You know the door handedness and it matches the hinge side already mortised into the frame
- The correct size and fire-rated slab for the unit's door schedule is on site
- Hinges and any lockset bore are either already machined into the slab at the factory, or you have the template to cut them yourself
- The sweep and any weatherstripping the job calls for are on site and sized to the slab thickness
What You Need To Know #
- A slab-only replacement means mortising the hinges into a frame that is already installed, instead of building a new jamb from scratch
- Check the slab for warp before you hang it. A twisted slab will never close and latch right no matter how carefully you set the hinges
- The margin between the slab and the frame stays a consistent 1/8″, the same standard used on every door type
- The sweep mounts to the bottom of the slab, not the frame, and has to compress evenly against the threshold or floor across the full width of the door
- Confirm door handedness before you start. Stand on the side the door swings toward you to find the hinge side; suppliers sometimes label doors by hand instead, which can name the same door the opposite way
- Hardware on these doors works the same as on any other door, and the fire rating does not change how you hang it. Each hardware piece is its own separate item
Tools Required #
Power Tools #
- Drill/driver - for hinge screws, closer prep if the job has it, and the sweep
- Trim router with a mortising bit - only needed if the slab is not already factory prepped for the hinges
Hand Tools #
- Tape measure
- Chisel set - for cleaning up hinge mortises
- Utility knife
- 2-foot level or torpedo level - the frame is already fixed, so you only need to check the slab hangs plumb, not plumb an entire jamb from scratch
- Screwdriver
Supplies #
- Hinge screws matching the factory hardware, or longer screws if a mortise needs a firmer bite into the frame
- Sweep mounting screws
Materials #
- Replacement door slab, factory prepped or field mortised for hinges and hardware
- Door sweep, sized to the slab width and thickness
- Hinges, if not carried over from the old slab
Installation Steps #
Step 1: Confirm the Frame and Slab Match #
Check the existing frame for damage, plumb, and hinge mortise locations before you touch the new slab. Measure the frame opening and compare it to the slab dimensions, width, height, and thickness all have to match. Confirm handedness against the frame: stand on the side the door swings toward you, and check that matches the hinge side already mortised in.
Step 2: Check the Slab for Warp #
Before mounting anything, sight down the edge of the slab or hold a straightedge against the face to check for warp. A twisted or bowed slab will bind or leave an uneven margin no matter how carefully you set the hinges. Send a warped slab back rather than fighting it through installation.
Step 3: Mortise or Confirm Hinge Locations #
If the slab came factory prepped, confirm the hinge mortises line up with the frame's hinge locations before you commit to anything. If you are field-mortising, transfer the hinge locations from the frame onto the slab edge, then cut the mortises to the hinge leaf depth with a chisel or a mortising bit. Dry fit the hinges in both the frame and the slab before you drive a single screw.
Step 4: Hang the Slab #
With a helper, lift the slab into the frame and engage the hinge leaves. Drive the hinge screws, starting at the top hinge so it carries the weight while you square up the rest. Close the door partway and check the margin on all three sides. It should read a consistent 1/8″, matching the standard used across every door type.
Step 5: Install the Sweep #
Measure the slab width at the bottom edge and cut the sweep to fit if it is not pre-sized. Hold the sweep in place with the door closed and mark the height that gives full contact with the threshold or floor across the whole width, without dragging. Screw the sweep to the bottom of the slab at that marked height.
Step 6: Test Door Operation #
Open and close the door through its full swing and check for binding at any point. Check that the sweep makes even contact with the floor or threshold across the full width when the door is closed, with no gap and no drag. If lockset hardware is part of this task, confirm the latch engages the strike plate cleanly.
Close-Out #
Sweep up any metal shavings from mortising along with any drywall or floor debris around the opening. We sweep, we do not shop vac. Stage any leftover hardware and packaging so the next trade, painter or hardware installer, knows the door is ready for their step. If lockset or closer hardware is not part of this task, note that clearly so it is not missed at punch out.
Quality Check #
- Door hangs plumb in the existing frame with no binding
- Margin reads a consistent 1/8″ on all three sides
- Slab shows no warp or twist when sighted down the edge
- Sweep makes full, even contact with the floor or threshold across the door's width
- Hinges are fully seated and screws are tight
- Door handedness matches the frame and the door schedule
- Area is swept clean of shavings and debris
Troubleshooting #
Door Won't Close Flush #
Usually means the slab is warped, or the frame's hinge mortises are not lined up correctly with the slab. Check the slab with a straightedge first. If the slab is straight, recheck hinge mortise depth and position.
Sweep Drags or Leaves a Gap #
Adjust the sweep mounting height. On an uneven floor it may need slight trimming, or an adjustable sweep may be the better product for that unit.
Margin Is Uneven #
Check that the hinge screws are fully seated and the slab is not binding at one hinge. Re-set the hinge screws one at a time and recheck the margin after each one.
Door Doesn't Match Handedness #
Stop and confirm before mortising any further. Order the correct hand slab if needed rather than trying to reverse a factory-mortised slab.
