Master Masonry Trade Tutorial

How to Build a Brick Arch: Step-by-Step Masonry Guide

Master the complete jobsite construction workflow: calculating odd voussoir stone counts, cutting rigid timber centering ribs, setting the skewbacks on supporting piers, and safely striking the folding wedges.

Interactive Tools for This Guide:
→ Brick Arch Calculator (Voussoirs & Keystone) → Arch Centering & Formwork Tool

Phase 1: Calculation and Dry-Laying

Before mixing a single batch of mortar, calculate the exact Intrados Arc Length using our Brick Arch Calculator. In structural masonry, the total count of voussoirs must always equal an ODD integer so that a single keystone sits squarely on the centerline crown.

Phase 2: Building and Supporting Timber Centering

The centering formwork carries the entire weight of wet masonry and workers until the keystone is driven. Fabricate two matching 3/4" plywood ribs cut with radius R_rib = R_finished − t_lagging, join them with 2x4 framing blocks, and screw 1x2 pine lath slats across the extrados curve.

Phase 3: Setting Skewbacks on End Piers

The skewback is the angled mortar bed cut into the supporting piers at the springline. It must sit perpendicular to the radius vector of the arch curve (angle α = 90° − θ/2) so compressive forces transfer cleanly into the solid masonry piers without sliding.

Phase 4: Laying the Voussoirs from Springing to Crown

Lay bricks symmetrically from both springing lines upward toward the crown. Never lay one side completely before starting the other, as unbalanced dead load can twist the timber centering formwork.

Phase 5: Driving the Keystone and Striking Wedges

Butter both vertical faces of the central keystone with mortar and slide it firmly into place at the apex crown. Allow mortar to cure for at least 48 to 72 hours, then tap out the folding timber strike wedges to lower the centering smoothly.

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Frequently Asked Questions

Common carpentry, masonry, and geometric questions regarding arch calculations and construction layout.

Q1 What type of mortar should be used when laying a brick arch?

Use ASTM C270 Type N mortar (medium strength, 750 psi) for general residential arches, or Type S mortar (high compressive strength, 1800 psi) for structural exterior arches subject to heavy lateral thrust and freeze-thaw cycles.

Q2 How long must the timber centering formwork remain in place?

Keep the timber centering and folding wedges securely in place for at least 48 to 72 hours under warm, dry conditions, and up to 7 days in cold or damp conditions before striking the wedges.