Fitting Skirting & Architrave: Mitre Cuts, Scribe Joints & Fixing Methods

Summary

Skirting boards and architrave are second-fix carpentry items — fitted after plastering and before decoration. They are the finishing trim that conceals the junction between floor and wall (skirting) or door frame and wall (architrave), and they make a significant difference to the quality perception of a room.

The craft is in the jointing. Perfectly fitting mitre cuts at external corners and scribed internal returns are what separate a quality result from a passable one. Timber moves with humidity changes — mitred internal corners will open as the timber dries in central heating, while a properly scribed joint remains tight because one piece overlaps the other.

Matching skirting profiles in older properties is one of the most time-consuming parts of the job. Victorian and Edwardian properties often have complex ogee or torus profiles that are not readily available off the shelf — a visit to an architectural salvage yard or a custom run from a local joiner may be required.

Key Facts

• Standard skirting profiles: Pencil round (simplest), ovolo, ogee, torus, chamfered, bar — profile choice should match the property's age and character
• Standard skirting heights for domestic: 75mm, 100mm, 125mm, 150mm, 175mm, and 225mm — taller skirtings suit higher ceilings
• Thickness: 15mm PAR (planed all round) is standard; 19mm or 25mm for heavier period-style boards
• Architrave standard width: 44mm, 57mm, 69mm, or 94mm; thickness typically 15mm or 19mm PAR
• Architrave reveal gap: Set architrave face 8–10mm back from the door lining edge (the "margin") — this is the reveal and should be consistent on all sides
• Fixing to plasterboard/studwork: Adhesive (e.g. grab adhesive) plus stainless or galvanised oval nails or lost-head nails
• Fixing to solid masonry (brick/block): Masonry plugs + screws, or cut nails driven into mortar joints, or construction adhesive + nails
• Nail size for skirting: 50mm or 65mm oval lost-head nails or 50mm cut flooring brads
• Nail spacing: 400–600mm on intermediate wall; always nail close to top and bottom edges of board and at both ends
• Mitre saw accuracy: 45° mitre is only accurate when walls and frames are perfectly square — always test-cut and adjust before final cut
• Scribing: Use a compass or offcut of matching skirting to scribe the profile onto the board at internal corners
• External corners: Always mitre at 45° — use a biscuit or loose tongue in a deep groove if the joint is in a heavy-traffic area
• MDF skirting: MDF boards are dimensionally stable (less movement) but heavier, must be fixed well, cannot be bent around curves, and must be primed on all cut edges before fitting or moisture absorption will cause swelling

Quick Reference Table

Detailed Guidance

Scribing Internal Corners

The scribe joint is the correct method for internal corners. It creates a joint where one board butts square to the wall and the second board is cut to the profile of the first.

Method:

1. Fit the first board square into the corner — it runs hard into the corner and is cut square at its far end
2. Hold the second board over the first, touching the wall
3. Use a compass set to approximately 10mm, and run the point along the face of the first board while the pencil scribes a line on the second board
4. Cut along the scribed line with a coping saw or jigsaw — cut slightly proud and test-fit, then pare back with a chisel or rasp until the joint is tight
5. The second board then has a profile cut to exactly match the face of the first — when pushed home it cups over the first board and sits tight

Why not mitre internal corners? A mitred internal corner opens as the timber dries — the gap typically appears at the top of the joint first. A scribed joint is tolerant of movement because the second board simply slides along the face of the first.

Cutting External Corners

External corners (e.g. around a chimney breast, door threshold, or column) are mitred at 45°.

1. Dry-fit and mark the exact corner point on both boards
2. Cut the first board at 45° with the mitre pointing toward the wall
3. Dry-fit and check the corner angle — many corners are not perfectly 90°. If the corner is out, bisect the actual angle with a digital angle finder and cut both boards at half that angle
4. Glue and nail the joint — always nail through the face of the mitre as well as into the wall
5. For a very tight corner, a biscuit (No. 0 or No. 10) in the mitre is worth doing for long runs where movement might otherwise open the joint

Fitting Architrave

Architrave surrounds the door lining on the wall face, concealing the junction between the lining and the plaster.

Marking the margin:

• The margin is the gap between the edge of the door lining and the face of the architrave — typically 8–10mm, consistent on all three pieces (two legs and the head)
• Use a pencil and combination square to mark the margin line around the lining face before cutting anything

Order of fitting:

1. Fit the head (horizontal piece) first — mark the precise length at each margin corner mark, cut both ends at 45°, and fix
2. Fit the legs — mark from the floor up to the margin corner mark, cut the top at 45° to match the head, cut the bottom square
3. Test all joints before nailing off — tap mitres tight with a block and mallet if there are small gaps

Fixing: 38mm or 50mm oval nails into the lining edge (50mm minimum material behind the lining face). Nail to the wall plaster side at 200–300mm centres — use 65mm oval nails into studwork or masonry anchors if the plaster is loose.

Working with MDF Skirting

MDF skirting is popular because it is pre-primed, dimensionally stable, and cheaper than timber. Key differences:

• Prime all cut ends immediately — unprimed MDF absorbs moisture at the cut edge and swells, lifting the paint finish
• Cannot be scribed easily — the profile crumbles when cut with a coping saw; use a fine-tooth blade and support the workpiece
• Heavier — plan fixings for MDF; adhesive-only is not reliable for tall, heavy profiles
• Cannot be sanded smooth across the face — MDF face paper tears unevenly; if it needs filling, use a flexible filler and prime before final coat

Gaps and Finishing

• Bottom gap (expansion gap): Leave 2–3mm gap at the floor for solid timber skirting — movement accommodation; this gap is concealed by the floor finish or a small bead
• Caulking: Fill the top edge of the skirting to the plaster with flexible decorator's caulk (not silicone), not filler — filler cracks as the skirting moves
• Nail holes: Fill with wood stopper or fine surface filler; sand flush when dry before decorating

Frequently Asked Questions

Should I mitre or scribe internal corners?

Always scribe internal corners for timber skirting and architrave. Mitred internal corners open up as timber dries — especially significant in new-build properties where timber moisture content may still be high. Scribing takes longer but produces a joint that remains tight.

My walls are not square at the corners — what do I do?

Most rooms are not perfectly square. For external corners, measure the actual angle using a digital angle gauge or bevel and bisect it for both cuts. For internal corners, the scribe technique automatically accommodates the angle because it copies the profile of the adjacent board regardless of the wall angle.

What is the correct way to deal with a gap between the back of the skirting and a wavy wall?

Wavy plaster walls are normal in older properties. Fix the skirting to the wall using a combination of adhesive and fixings, pressing the skirting tight at the fixing points and allowing the adhesive to bridge the gaps. For particularly wavy walls, pack out the skirting at fixed points with offcuts of hardboard or ply to create a consistent face, then fill with caulk at the top edge.

Can I fit skirting on a wet screed floor?

No — wait until the screed has cured and achieved its final moisture content before fitting skirting and architrave. Fitting skirting to a wet screed will cause moisture to wick up into the skirting, causing warping and paint adhesion failure. Use a moisture meter; screed moisture content should be below 75% RH before fitting timber finishes.

Do I need to use adhesive on solid masonry walls?

On solid brick or block walls, construction adhesive (e.g. No Nails, grab adhesive) combined with mechanical fixing (cut nails into the mortar joint or masonry screws into plugged holes) is the standard approach. Adhesive alone is not reliable for skirting because the weight and movement forces over time will break the bond, especially near floor level where moisture fluctuations are greater.

Regulations & Standards

• BS 1186 (Timber for joinery — specification for timber) — grading requirements for joinery timber

• No specific Building Regulations notification required for skirting and architrave fitting

• MDF — must comply with BS EN 622-5 for dry conditions; use moisture-resistant (MR) grade MDF in bathrooms and kitchens

• TRADA — Timber Moisture Content Guide — Moisture content targets for second-fix joinery

• Guild of Master Craftsmen — Joinery Standards — Quality benchmarks for finish joinery

• NHBC Technical Standards Chapter 8.2 — Movement joint and moisture guidance for internal joinery

• door frames — Door lining installation — fit before architrave

• first fix second fix — Sequence of second-fix joinery

• stud walls — Stud wall construction — fixing points for skirting