Building Corner Leads and Running Bond Wall Courses

Building Corner Leads and Running Bond Wall Courses

Corner leads are the foundation of any coursed brick wall. They establish plumb, level, and spacing for every course that follows. A lead is a stepped, pyramid-like section of brick built at each end or corner of a wall. When both leads are complete, a string line pulled between them guides each intermediate course. Getting the leads right means the filled wall between them will be right; getting them wrong means every error is locked in as the wall grows.

What a Running Bond Lead Looks Like

In running bond — the most common brick pattern — each course is offset from the one below by half a brick length. A six-course lead therefore starts with the widest course at the bottom and steps back by one brick per course as it rises. The result looks like a staircase when viewed from the side. The racking keeps the lead plumb while giving you a clean edge against which to pull your string line for each intermediate course.

Setting Up Before You Lay a Brick

Before mixing or opening mortar, complete your safety checks. Wear safety glasses, leather-palm gloves, and steel-toed boots at all times on the lab floor. Keep the work area clear of tripping hazards. When carrying brick, stack no more than you can handle safely — crushed fingers from dropped brick are among the most common masonry injuries. Wet mortar is caustic; if it contacts skin, rinse immediately with clean water. Have a first-aid kit within reach.

Set up your story pole alongside the planned lead location. A story pole is a straight rod marked at each mortar-joint interval — for standard modular brick on a 3/8-inch joint, each course mark is at 2-5/8 inches (brick height) plus 3/8 inch (joint) = 3 inches per course. Six courses will rise exactly 18 inches on a properly laid story pole. Check that your work surface is clean, dampened if required by conditions, and that your mortar is pre-batched Type S, mixed to the correct consistency — it should hold its shape on the trowel without slumping but spread smoothly when thrown.

Building the First Lead: Step by Step

Throw and furrow the bed joint. Using your brick trowel, throw enough mortar to cover the footprint of three to four bricks. Draw the tip of the trowel down the center to create a slight furrow — this helps mortar spread under the full face when the brick is pressed down.

Set the corner brick. Place the corner brick firmly, tapping with a rubber mallet to bring it to the correct height. Check plumb on two adjacent faces with your 4-foot mason's level. Check level along the course. The brick must be plumb and level before you move on.

Butter head joints and lay the first course. For each brick added to the first course, butter the head joint on the end of the brick being placed — not on the brick already set. Press the brick firmly against the previous one so mortar squeezes out slightly at the joint face. Head joints must be full; voids create moisture paths and weaken the wall.

Rack back each successive course. Each course in the lead starts one half-brick shorter than the course below. Before laying the second course, apply a full bed joint over the first. Set the corner brick, check plumb and level again, then lay the remaining bricks for that course. Repeat, course by course, up to six courses. Check plumb continuously with your level held against the face and side of the lead.

Filling Between the Leads

Once both leads are complete, pull a string line between them for each course. Use line blocks secured to the outer face of each lead brick at the exact course height marked on your story pole. The string line must be taut — a sagging line produces a bowed wall. Lay bricks to the string, keeping the top face and outer face of each brick just touching the line without pushing it. This is called "laying to the line."

Tool the joints after the mortar reaches thumbprint hardness — when a firm thumb press leaves a clean print but mortar does not smear. Tooling with a jointing iron compresses the mortar, improves weather resistance, and produces a uniform concave profile. Work bed joints first, then head joints. Brush away loose mortar crumbs with a soft brush; sponge the face lightly if needed.

Checking Your Work

Use the 4-foot mason's level to check plumb at multiple points along the wall — not just at the leads. Check level along each course with the level resting flat on the brick surface. Use the tolerance checklist: plumb must be within 1/4 inch over the full six-course height; level must be within 1/8 inch per 4-foot run; every joint must measure 3/8 inch, plus or minus 1/8 inch. After raking, no void should be visible in any joint. Record every measurement in your lab log and note any correction you made and why.

Common Errors and How to Fix Them

If your lead drifts out of plumb, do not try to correct it by tilting one brick — you will create a worse error two courses later. Remove the offending brick, clean the bed joint, re-lay with corrected mortar thickness, and recheck. If head joints are inconsistent, work on your buttering technique: apply mortar to the full end of the brick, press firmly, and let the squeeze-out tell you the joint is full. Thin joints mean too little mortar was applied; fat joints mean too much or the brick was not pressed firmly enough.