How to fit architrave

Video by Tommy's Trade Secrets. This walk-through is based on the video "Tommy's Trade Secrets — How To Fit Architrave" from Tommy's Trade Secrets, a long-running UK trade and DIY channel that explains carpentry tasks in exactly the kind of clear, practical way a tradesperson would on the job. The section on marking and cutting the head piece first is worth paying attention to before you start.

1. Choose your architrave profile and prepare the surface

Architrave comes in a range of profiles — from plain square-edge to ogee, torus, and various other moulded shapes. In most UK houses built from the 1960s onwards you will find a fairly simple ovolo or torus profile. If you are replacing damaged pieces and need to match existing architrave, take a short offcut to the timber merchant so they can match the profile exactly. Getting it wrong and ending up with a slightly different moulding on one door looks worse than leaving the damaged piece alone.

Before you start, strip off any old architrave carefully. A thin pry bar and a block of wood to protect the plaster will do it cleanly without gouging chunks out of the wall. Sand or scrape off any remaining adhesive or paint ridges so the new pieces will sit flat. If the plaster is blown or crumbling at the edge, fill and let it dry before you try to nail into it — a nail into soft plaster will pull straight back out.

2. Mark the reveal on the door lining

The reveal is the amount of door lining face that stays visible between the edge of the frame and the inner edge of the architrave. A standard reveal is around 6–8 mm. Consistent reveal on all three sides (two legs and the head) is what makes the job look professional; inconsistent reveal is immediately obvious and looks sloppy.

Use a combination square or a small offcut set to your chosen reveal distance. Run a pencil line down both upright linings and across the head lining. This line is where the inner edge of your architrave will sit. Take your time here — it is the reference for every cut you make.

3. Cut and fit the head piece first

The head (top horizontal) piece is cut first. Hold it against the head lining with the inner edge on your reveal line, and mark where the reveal lines on the two upright linings cross it at each end. These marks give you the short point of each 45-degree mitre cut.

Set your mitre saw to 45 degrees and cut with the long face of the mitre towards you — the tail of the cut should be on the waste side. Cut the first mitre, then offer the piece up to check it before cutting the second end. It is much better to sneak up on the final length than to cut it too short in one go. To be fair, every experienced carpenter has cut a head piece a centimetre too short at least once.

4. Cut the two upright legs

With the head piece temporarily pinned in position, hold each upright leg in place with its inner edge on the reveal line. Mark the short point of the mitre at the top where it meets the head piece. Cut the 45-degree mitre at the top — note that this mitre runs the opposite way to the head piece. The bottom of each leg is a straight 90-degree cut, sitting on the floor or on the skirting board.

If skirting board is already fitted, the architrave leg sits in front of it, butted against it at the bottom. If you are fitting both at the same time, the skirting butts into the architrave and a small plinth block can be used to cap off the join neatly — though in modern UK housing, the simple butt joint with the architrave scribed or coped into the skirting is the most common approach.

5. Fix the architrave in place

Apply a thin bead of wood adhesive along the back face of each piece before pinning — this stops any gaps opening up as the timber moves with temperature and humidity changes, which it will. Use 50 mm oval nails or lost-head nails, punching them just below the surface with a nail punch. Fix into the door lining on the inner edge and into the stud or blockwork behind the plaster on the outer edge. Space fixings every 400–500 mm along each leg.

Check the mitre joints are tight before the adhesive sets. If a mitre has a small gap, a touch more adhesive and a clamp or a couple of strategically placed panel pins through the mitre itself will pull it together. On soft pine architrave, clamping with masking tape across the joint works well enough while the glue goes off.

6. Fill, sand, and finish

Punch all nail heads below the surface and fill with a fine interior filler or decorator's caulk. Caulk is better for the joint between the architrave and the plaster wall — it stays flexible and does not crack as the building moves. Filler is better for the nail holes in the timber face because it can be sanded flat.

Once dry, sand lightly with 120-grit paper, wipe down with a damp cloth, and paint. Two coats of a decent satin or eggshell over a coat of primer will give a hard-wearing finish. That said, if the rest of the woodwork in the room is gloss, match it — mixing sheens on the same door frame looks odd. Step back and admire the difference a tidy set of architrave makes. It is one of those jobs where the result is immediately obvious.

When to call a handyman

Call Richard if the door frame is badly out of square and the mitres are not closing up no matter how you cut them, if you are fitting architrave on multiple doors in one go and want it done in a day, or if you do not own a mitre saw and are not confident cutting accurate 45-degree angles by hand. Poorly cut mitres are very visible and hard to disguise once painted. Get in touch and Richard can sort the architrave at the same time as any other joinery work that needs doing.