Laying CMU and Brick: Leads, Lines, Coursing & Full Joints

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Alright, Laying CMU and Brick: Leads, Lines, Coursing & Full Joints. Don't let the plain title fool you. Here's the part that actually matters on the job: A wall is built from the corners out, so lay out the coursing on a story pole, build plumb leads, stretch a tight line, and give every unit a full bed and a full head joint. Learn it well and the wall is straight the first time, the joints shed water, and the inspector has nothing to write down.

The intro course covered the tools and the materials. This lesson is the method: the order of operations a journeyman follows without thinking about it, and why each step exists.

Layout and the first course

Everything starts on the footing or slab. Snap the wall lines from the control points on the drawings, not from the edge of the footing, which was never that accurate. Then dry-lay the first course with a 3/8-inch gap between units to check the bond: in running bond, every course should work out to full and half units with no slivers at the corners or the openings. If the dimension does not work, this is the moment to adjust the joint width a hair across the run or to shift an opening by a joint, with the superintendent's agreement, not after the lead is up.

Check the dowels against the cell layout before a block is laid. A dowel that lands on a web cannot be bent into the cell at any angle you like; TMS 602 limits the slope to 1 in 6, and anything worse goes to the engineer. The first bed joint sits on the foundation and absorbs its irregularity; TMS 602 allows it between 1/4 inch and 3/4 inch thick. The first course of hollow block gets a full mortar bed, face shells and webs, because it carries everything above it.

Coursing and the story pole

Masonry is modular. One nominal 8-inch block course equals three courses of modular brick with 3/8-inch joints, which is why the brick on a cavity wall meets the block ties every third course. Mark a story pole, or set corner poles, with every course height, sill, head, bond beam, and the top of wall, taken from the elevations and the lintel schedule. The pole, not the tape, is the reference for the leads. The modular spacing rule does the same job for brick: scale 6 lays six courses in 16 inches, standard modular coursing.

Building the leads

Leads are the corners and ends of the wall, built first and plumb, so the line between them can carry the rest of the wall. Build a block lead four or five courses high, racked back one half unit per course so the wall can be tied into it without a vertical seam. On each course, check plumb on both faces, level along the top, and straight along the face with the 4-foot level, and check the course height against the pole. An error in the lead is copied into every unit laid to the line.

Laying to the line

Stretch the line from lead to lead on line blocks or pins, pulled tight enough that it does not sag over a 40-foot run. Set every unit so its top outside edge is level with the line and about a sixteenth of an inch off it; a unit touching the line pushes it out for everyone down the wall. Move the line up with each course.

For block, spread the bed for three or four units at a time, no further, so the mortar does not skin over. Stretcher block goes up with the wider face shells up; the tapered cores leave a broader surface on top for the next bed. Butter both ears of the end with a full head joint, shove the unit into place to compress it, and tap it down to the line with the trowel handle. Hollow units get face-shell bedding, except where cells will be grouted, where the webs beside the grouted cell are also mortared to confine the grout.

Brick is laid with a full bed, a light furrow at most, and a full head joint buttered on the end before the unit is shoved home. Deep furrows and slushed head joints are the two main water paths through a brick wall. Pull from three or more cubes at once so the color range blends instead of banding.

Closures, cuts, and tooling

The closure, the last unit in a course, gets mortar on both of its ends and on the ends of the units it goes between, then is lowered straight in. A closure dropped in with one dry side is a leak. Cut units on the wet saw where the cut will show, and never set a chipped face out. Tool the joints when the mortar is thumbprint hard: a concave or V joint compresses the mortar against the units and sheds water, and the timing must be consistent across the wall or the joints change color. Brush off the burrs and cut the mortar tags off the back of the wall before they harden in the cavity.

Going Deeper (Intermediate)

Keep the vertical cells aligned as the wall rises so grout can drop through; one unit set a half inch off line blocks the cell. Keep mortar out of cells to be grouted and knock the fins off as you go, because TMS 602 requires protrusions over 1/2 inch to be removed before grouting. At openings, use sash or jamb block so the frame and the control joint have something to key into. Bond beam and lintel courses are set from the pole, not counted up from the floor.

Advanced / Pro-Level

Pros plan the wall in scaffold heights. A mason lays fastest between the knee and the chest, so the crew builds to scaffold height, the tenders raise and restock, and the leads for the next lift are run while the stock comes up. Pros also read the backup before the veneer: on a cavity wall the block, tie, and brick coursing are reconciled on the pole before a single brick is laid, and the flashing lines are marked on the backup.

Practice Challenge

You are laying out a 40-foot CMU wall with a 3-foot door opening 6 feet from one corner. The dry layout leaves a 3-inch sliver at the door jamb. What do you do? (Answer: do not lay the sliver. Check whether the opening can shift by half a unit within the door schedule, or whether the joint width can be adjusted slightly across the run; get the superintendent's agreement, mark the pole and the layout, then build.)

In Practice

A crew that dry-lays the first course, checks the dowels, and builds true leads lays the rest of the wall to the line almost without thinking. A crew that starts laying off the footing edge is cutting slivers at the jambs by noon and chasing plumb all week.

Common Mistakes to Avoid

• Laying the first course before the dowels and the bond are checked
• Spreading bed joints too far ahead so the mortar skins over
• Crowding the line, so every unit down the wall drifts out
• Slushing head joints instead of buttering them full
• Tooling joints at different stiffness, leaving light and dark bands

Takeaway: A wall is built from the corners out, so lay out the coursing on a story pole, build plumb leads, stretch a tight line, and give every unit a full bed and a full head joint.

Educational content only — not design, engineering, or hands-on instruction, and not a substitute for training under a qualified mason or the judgment of a licensed design professional. Follow TMS 402/602 and the building code as adopted in your jurisdiction, the project specifications, the manufacturer's instructions, OSHA 29 CFR 1926, and your employer's procedures for your work.