How We Upcycled Old Door Casing to Make Plain Doors Look Custom

When we replaced the narrow wood casing around our door frames, the old material seemed too useful to discard. Cut into simple rectangular frames and attached to basic hollow-core doors, it added depth, shadow and the appearance of custom millwork using material that might otherwise have ended up in the rubbish.

Originally published on May 21, 2013, this feature has been substantially updated with expanded guidance.

There was nothing mechanically wrong with the original doors.

They opened, closed and separated one room from another.

That was about all they offered.

They were the most basic kind of flush interior doors: flat, lightweight and almost entirely without architectural detail. Hollow-core doors typically use thin facings over a lightweight honeycomb structure, which keeps them affordable but gives the surface little depth or visual weight.

The opportunity appeared when we replaced the narrow wood moulding surrounding the door frames with wider MDF trim.

The moulding around a door is commonly called door casing, door trim or architrave. For simplicity, we will use door casing throughout this guide.

Instead of throwing the old casing away, we cleaned it, cut it into rectangular frames and attached it to the faces of the plain doors.

Once the casing and door were primed and painted together, the separate pieces read as one panelled design.

The doors were still inexpensive hollow-core doors.

They simply no longer looked like the least expensive doors in the building.

Why old door casing is worth saving

Narrow door casing is routinely removed during renovations when homeowners replace it with wider or more decorative trim.

Much of it is perfectly usable.

The old casing from your own project is the obvious place to begin, but similar material can also appear at architectural salvage centres, building-material reuse shops and curbside renovation piles. Only take material that is clearly being discarded and that local rules allow you to remove.

Look for long, straight pieces without deep rot, severe warping or extensive splitting. Small nail holes and dents are not a problem; those can be filled during finishing.

The profile does not need to be elaborate. Once arranged into well-proportioned rectangles and painted the same colour as the door, even modest casing can create convincing depth and shadow.

What you will need

• Salvaged wood door casing
• Tape measure
• Combination square
• Pencil
• Mitre saw, or a mitre box and handsaw
• Fine-grit sandpaper
• Construction adhesive compatible with the door surface and casing
• Short brads or pin nails
• Hammer, nail set or brad nailer
• Wood filler
• Paintable decorator’s caulk
• Bonding primer
• Interior door-and-trim paint
• Screwdriver
• Two sawhorses or another stable work surface
• Eye and hearing protection

Before you begin

This project is intended for an ordinary interior door.

Do not modify a fire-rated, exterior or specialised acoustic door without checking its construction and certification requirements.

When practical, remove the door from its hinges and lay it flat across two padded sawhorses. It is far easier to measure, glue and align the casing on a horizontal surface.

Before lifting the door off, mark its top and hinge edge lightly in pencil. A plain slab can be surprisingly easy to turn around once it is lying flat.

Remove the handle and any other hardware that could interfere with the layout.

If the salvaged casing is old or its paint history is unknown, do not begin by dry-sanding it. Sanding, scraping and cutting older painted trim can produce hazardous lead-contaminated dust. Test the finish first and follow appropriate lead-safe working practices when necessary.

Step 1: Prepare the salvaged casing

Remove any remaining nails before cutting the trim.

The cleanest method is usually to grip each finishing nail from the back with end-cutting pliers and pull it through the back of the casing. Driving it back through the finished face can enlarge the original hole or break away the visible surface.

Scrape away loose caulk, dried adhesive and raised paint edges.

Inspect each piece as you work. Set aside anything badly twisted or cracked. A bowed length may appear usable on the floor but will resist the adhesive and pull away from the door later.

Lightly sand the usable pieces until the faces and edges feel smooth. The goal is not necessarily to remove every layer of old finish. You need a clean, stable surface that can be primed and painted.

Step 2: Plan the panel arrangement

This is the most important part of the project.

The casing profile can be simple. What makes the finished door look intentional is proportion and consistent spacing.

We arranged the old casing into three stacked rectangular frames on each face of the door. The repeated shapes gave the flat slab the suggestion of a traditional panelled door without attempting to imitate one exactly.

Lay the pieces loosely on the door before making any cuts.

Consider:

• the distance from the top and bottom of the door;
• the space between each panel;
• the position of the handle;
• the hinge locations;
• the distance between the casing and the outer edge; and
• whether the moulding could contact the door stop when the door closes.

Keep the design far enough inside the perimeter to clear the frame and hardware.

On our doors, the original layout came close to the hinge side, which required additional trimming around the hinge area. The easier solution is to bring the entire arrangement slightly farther towards the centre of the door.

Step 3: Mark a consistent layout

Once the proportions look right, mark the outer corners of every proposed frame lightly in pencil.

Use a square and straightedge rather than measuring each point independently. Small measuring errors become very visible when several rectangles are stacked on the same door.

A simple story stick is useful here.

Take a straight offcut and mark the top, bottom and spacing of each panel on it. You can then transfer the same measurements to the opposite edge and to other matching doors without repeatedly reading the tape.

Check the diagonals of every rectangle. When both diagonal measurements are equal, the layout is square.

Do not begin cutting until the full arrangement has been marked and checked.

Step 4: Cut the mitred frames

Set the mitre saw or mitre box to 45 degrees.

Cut one end of the first piece, position it against the marked layout and transfer the measurement for the opposite end directly from the door.

Working from the actual layout is more reliable than cutting every piece from a list of calculated measurements. Small variations in reclaimed trim and door dimensions can accumulate quickly.

Complete one rectangle at a time.

Dry-fit all four pieces on the door and check the corners before moving to the next panel. A tight mitre should close neatly without needing excessive filler.

Once you have one correctly proportioned frame, you can use its matching pieces as references for the other panels—but continue checking each cut against the door.

Step 5: Dry-fit the complete design

Lay every cut piece in its final position.

Step back and look at the entire door rather than concentrating only on the joints.

Check that:

• all three frames are centred;
• the side margins are equal;
• the spaces between panels are consistent;
• the arrangement clears the handle and hinges; and
• no piece comes too close to the door edge.

Open and close the door with the casing held temporarily in place when possible. This is the easiest time to discover that a piece touches the frame or door stop.

Make every adjustment now.

Once adhesive is applied, the available correction time becomes much shorter.

Step 6: Attach the casing

Remove one frame at a time while leaving the remaining pieces in position as visual references.

Apply a narrow, continuous bead of compatible construction adhesive to the back of the first piece. Use enough to create a reliable bond, but not so much that large amounts squeeze onto the door face.

Position the piece on the pencil line and press it firmly into place.

Add a few short brads or pin nails to prevent movement while the adhesive cures. The adhesive should provide the primary bond; the brads act mainly as temporary clamps.

Check the fastener length before using a nailer. It must be appropriate for the combined thickness of the casing and door and must not risk reaching the opposite face.

Attach the remaining three pieces, adjusting the mitres before the adhesive begins to set.

Wipe away fresh squeeze-out immediately with the method recommended by the adhesive manufacturer.

Repeat the process for the remaining frames.

Step 7: Fill the joints and nail holes

Allow the adhesive to cure for the recommended period.

Set any visible nail heads slightly below the surface, then fill the holes and imperfect mitres with wood filler.

Once the filler has dried, sand it flush without rounding over the decorative profile.

Run a fine bead of paintable caulk along any narrow gaps between the casing and the door. Smooth it carefully with a damp finger or caulking tool.

The caulk is what helps the applied trim look integrated rather than simply glued on.

Do not use it to disguise large cutting errors. Wide or uneven gaps are better corrected by recutting the affected piece.

Step 8: Prime the door and casing together

Lightly sand the complete door to dull the existing finish and remove rough areas.

Vacuum the dust and wipe the surface clean.

Apply a bonding primer suitable for both the door face and the salvaged casing. Pay particular attention to bare end grain, filled nail holes and areas where old finish has been exposed.

Priming the entire assembly together begins the visual transformation. Once the old casing and flat door share the same uniform surface, they start to read as one piece of millwork.

Allow the primer to dry fully, then sand lightly where needed.

Step 9: Apply the finish paint

Use a durable interior paint suitable for doors and trim.

A satin or semi-gloss finish is practical because it stands up well to regular handling and is easier to wipe clean than a flat wall paint.

Paint the casing profiles first, working the brush into the corners and mitres. Then roll or brush the flat areas of the door, maintaining a wet edge.

Watch for drips along the lower edges of the casing.

Allow the first coat to dry, sand lightly if needed and apply a second finish coat.

Give the paint sufficient time to harden before reinstalling the hardware or hanging the door. Paint that feels dry to the touch may still be soft enough to mark around hinges and handles.

Step 10: Reinstall the hardware and hang the door

Reattach the handle and hinges.

Before tightening everything fully, check that the casing does not interfere with the hinge leaves or hardware.

Hang the door and move it slowly through its complete swing.

Confirm that it:

• clears the frame and door stop;
• latches without resistance;
• does not rub at the hinge edge;
• opens fully; and
• remains properly aligned in the opening.

Make small hinge adjustments where necessary rather than forcing the door closed against newly added trim.

One Thing I Learned

The success of this project does not depend on expensive moulding.

It depends on spacing.

When the margins are consistent, the corners are square and the three frames relate properly to the dimensions of the door, inexpensive salvaged casing can look surprisingly convincing.

When the spacing is slightly wrong, even beautiful new trim can look improvised.

Spend more time arranging the first door than cutting it. Once that layout is right, it becomes the template for every door that follows.