How to Install Door Architrave for a Clean Finish
A door lining can be perfectly square and still look unfinished until the architrave is fitted. The moulding covers the gap between the lining and wall, protects vulnerable plaster edges and creates a clear transition into the room. Knowing how to install door architrave properly comes down to accurate setting out, clean cuts and fixing each length without pulling it out of line.
For most internal doors, moisture resistant MDF architrave is a practical choice. It is stable, supplied in consistent lengths and profiles, and arrives ready for priming or fully finished depending on the option selected. Pine and oak need slightly different treatment when cutting and finishing, but the fitting method remains broadly the same.
Before you install door architrave
Fit architrave after the door lining is secure and the surrounding wall is dry, but before the final decorating stage. If you are replacing old trim, remove it carefully first. Cut through old caulk with a sharp knife, prise the moulding away in stages and avoid damaging the plaster that will sit behind the new piece.
Check the door lining for straightness before taking measurements. A lining that is proud of the wall in one area, or recessed in another, may need packing, a small amount of sanding or a flexible decorator’s caulk line after fitting. Do not assume both sides of an opening are identical, particularly in older properties.
You will normally need a tape measure, pencil, combination square, mitre saw, fine-tooth blade, grab adhesive, panel pins or a second-fix nail gun, hammer and nail punch. Keep a spirit level close by too. A pin nailer speeds up repetitive work, but hand-driven lost-head nails are perfectly suitable for a single doorway.
Choose the profile and width before you start. Narrow, square-edged profiles suit contemporary rooms, while stepped, ogee or torus-style mouldings usually work better in traditional settings. Matching the architrave to your skirting board gives the room a considered finish. If you are unsure about profile scale or material, ordering free samples before committing to full lengths can prevent an expensive mismatch.
Set out the reveal line first
Architrave is not fitted flush to the inside edge of the door lining. Instead, it sits back by a consistent reveal, usually around 5mm. This visible strip of lining creates a neat shadow line and stops the architrave interfering with hinges or the door itself.
Use a combination square to mark a 5mm reveal on both vertical sides of the lining and across the head. Make several light pencil marks, then join them with a straightedge. The line must be consistent, because it is the reference for every piece of architrave.
There are exceptions. A very narrow lining, unusual hinge placement or an existing period detail may call for a smaller reveal. The key is to choose the dimension before cutting and keep it the same across the opening. Check that the proposed position leaves enough clearance for the door to open fully.
Measure and cut the two side lengths
The side pieces are generally fitted first. Measure from the finished floor level to the point where the top mitre will meet the horizontal head piece. If carpet, engineered wood or tiles are still to be fitted, allow for their finished height. Architrave cut to an unfinished subfloor can end up too short once the floor covering is installed.
For a standard mitred arrangement, each upright has a 45-degree mitre at the top, with the long point on the outside edge of the architrave. The bottom is normally cut square. Mark each piece clearly as left or right before cutting. This simple step avoids wasting a length by cutting the mitre in the wrong direction.
Cut slightly long if the opening is irregular, then trim back gradually. A sharp, fine-tooth blade helps prevent breakout on primed MDF and gives a cleaner edge on oak or pine. Support long lengths on both sides of the saw so the moulding stays flat and the mitre remains accurate.
Dry-fit the first side piece against the reveal marks. Check that its inner edge follows the line from floor to top, and that the mitre lands where expected. Repeat on the opposite side. If the wall bows away from the lining, press the architrave into the best position rather than forcing it to follow every hollow in the plaster.
Cut and test-fit the head piece
Measure the head piece from the outside, or long point, of one upright mitre to the outside of the other. The head architrave needs opposing 45-degree mitres, so its length is determined by the visible outside span, not the width between the lining legs.
A useful approach is to hold the two un-fixed uprights in place and take the measurement directly between their outer mitre points. Cut the head piece fractionally long, offer it up, then shave off a small amount if required. A joint that is a touch tight can be refined. A joint cut short leaves a visible gap that filler will not disguise well.
Dry-fit all three pieces together before applying adhesive. Look along the face of the moulding and check the profile aligns through both corners. If one mitre opens at the front or back, the cause may be an inaccurate 45-degree saw setting, a twisted length or an uneven door lining. Correct the cut rather than relying on caulk.
Fix the architrave securely without overdoing it
Apply a continuous, modest bead of grab adhesive to the back of the first upright. Keep the adhesive away from the inner edge so it does not squeeze onto the reveal line. Position the piece against the marks, press it firmly into place and check it remains plumb.
Add panel pins or brad nails at roughly 400mm intervals, with extra fixings near each end and around the mitre. Drive them through the thicker sections of the profile where possible. On MDF, pins provide immediate hold while the adhesive cures and reduce the risk of the moulding moving back from an uneven wall.
Do not use excessive adhesive or too many nails. Too much adhesive creates mess and makes future removal unnecessarily destructive. Over-pinning can split timber architrave and leaves more holes to fill. For oak, drill fine pilot holes if you are hand nailing, and use suitable fixings that will not stain the timber.
Fit the second upright in the same way, then fix the head piece. Before nailing the head, press both mitres together and make sure the reveal remains straight. A small pin driven at an angle through the mitre area can help hold a stubborn corner closed, but avoid firing directly through a delicate moulded edge.
Deal with uneven walls and awkward details
Walls are rarely perfectly flat, especially after plastering or in period homes. If there is a minor gap behind the outer edge of the architrave, adhesive and a few well-placed pins will usually hold it neatly. For a larger hollow, pack behind the moulding with a thin timber shim before fixing. This prevents the architrave flexing when knocked later.
Where the floor slopes, keep the top mitres and reveal level and trim the bottom of the upright to suit the floor. The eye is drawn to the head joint and the line around the door, not to a slight variation at floor level. If you are using plinth blocks, the vertical architrave can terminate on the block instead, removing the need for a mitred head joint and making installation more forgiving.
For very wide door openings, check whether your supplied length is sufficient before cutting. Made-to-specification lengths reduce unnecessary joints, but always plan the order of cuts so the best factory ends are used on the most visible mitres.
Fill, caulk and finish the fitted architrave
Once the adhesive has cured, punch nail heads just below the surface and fill them with a suitable wood or MDF filler. Sand lightly with fine abrasive paper once dry. Take care not to flatten sharp profile details.
Apply a narrow bead of decorator’s caulk along the outer edge where the architrave meets the wall, and use flexible caulk for small gaps at the lining if needed. Wipe it smooth straight away with a damp finger or finishing tool. Caulk is for fine finishing gaps, not for hiding poor mitres or badly bowed cuts.
Prime bare pine or MDF cut edges before painting. Pre-primed MDF still benefits from sealing any freshly cut ends, while fully finished boards should only need careful touch-up where cuts have exposed the core. Oak is usually finished with an appropriate clear oil, lacquer or stain system, with the end grain treated carefully to achieve an even appearance.
Take a final look from across the room as well as close up. Clean mitres, an even reveal and a profile that matches the skirting will do more for the doorway than extra filler ever will. If one joint needs adjustment, make it now, before paint turns a small fitting issue into a permanent distraction.