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newSchoolWorks.com › VoTechWorks › Building & Construction › Masonry › Stone Masonry: Selection, Layout, and Construction › Lesson 6
BLD-MASO04-04 · Lesson 6 · 18 clock hours · lab

Building a Stone Wall Panel: Coursed Ashlar and Random Rubble Applications

Objective. Students will build a freestanding single-wythe stone wall panel at least 3 feet long and 4 courses high, selecting units, cutting as needed, setting in mortar, and finishing joints to produce a wall plumb within 1/4 inch, level within 1/8 inch per 4-foot run, and free of open joints.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional engineer or master tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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Building a Stone Wall Panel: Coursed Ashlar and Random Rubble Applications

Stone masonry is one of the oldest building trades, yet its standards for plumb, level, and bond are as demanding today as ever. This lab brings together everything you have learned about stone selection, mortar, layout, and jointing into a single freestanding panel that must meet measurable quality standards.

Choosing Your Pattern

Coursed ashlar uses stones cut or selected so their bed joints run in continuous horizontal lines across the wall. Stones within a course need not be the same length, but all share the same height. The result looks orderly and regular. You must maintain consistent joint width—typically 3/8 inch to 1/2 inch—and stagger vertical (head) joints by at least one-quarter of the stone length above and below.

Random rubble uses undressed or minimally dressed stone of irregular shape and size. There are no continuous horizontal courses. The mason must still control bond, placing larger units at the base and corners, fitting smaller units into voids, and ensuring no vertical joint runs through more than two successive layers. Random rubble looks informal but demands careful unit selection so the wall locks together structurally.

Whichever pattern you are assigned, sketch your layout on paper before mixing mortar. A layout sketch saves material, catches fit problems early, and keeps your bond pattern honest.

Stone Selection and Preparation

At the supply yard, sort stones by size and shape. For coursed ashlar, group units by height first. For random rubble, set aside large anchor stones for corners and bond stones. Reject units with through-cracks or spalling faces that could split under load or freeze-thaw cycling.

Cutting is done with a wet saw for precision or a chisel and mason's hammer for rough shaping. The wet saw blade must stay continuously wet during the cut—never run it dry. Wear safety glasses or a face shield, hearing protection, and cut-resistant gloves when using either the wet saw or hand tools. Secure the stone firmly before each cut; a shifting unit can bind the blade or deflect the chisel unpredictably.

Setting the Foundation Course

The first course is the most critical. Dry-lay it completely before applying any mortar. Check for fit, confirm your bond pattern, and mark unit positions lightly with chalk. Spread a full mortar bed of Type S mortar—appropriate for exterior and structural stone applications—approximately 3/4 inch thick. Set each stone with a slight rocking motion and tap with a rubber mallet to seat it. Check level in both directions after each unit. Head joints must be fully buttered on at least one face of adjacent stones so the joint is filled solid with no voids.

Building Up: Bond and Bond Stones

As you build higher, maintain the stagger rule: no head joint should align with a head joint in the course directly below or above it. Every 2 to 3 feet of wall length—and at each corner—set a bond stone (also called a through stone or tie stone) that runs from the face toward the back of the wall, locking the wythe together. Bond stones prevent the wythe from splitting apart as a single plane of weakness.

At corners, alternate which stone overlaps: course one has the left-side stone running to the corner face; course two has the right-side stone doing the same. This alternating overlap is the corner bond, and it is essential for structural integrity.

Check plumb and level every two courses. Do not wait until you finish the panel to discover a 1/2-inch error—it is nearly impossible to correct without tearing down. Use a 4-foot level held against the face and a plumb bob dropped from the top edge. The specification for this lab is plumb within 1/4 inch over the full panel height and level within 1/8 inch per 4-foot run.

Tooling Joints

Joint tooling serves two purposes: it compresses the mortar surface to resist water penetration, and it gives the wall its finished appearance. Tool joints when the mortar is thumbprint-hard—firm enough to hold a thumbprint without mortar sticking to your thumb, but not so hard that tooling tears rather than compresses. A convex (rodded) jointer is the standard tool for stone work. Draw it along the joint in one smooth pass. Tool bed joints first, then head joints. Wipe any mortar smeared on the stone face with a damp sponge while the mortar is still fresh; cured mortar on face stone requires acid cleaning and risks staining.

Self-Inspection and Quality Control

At completion, use the program quality-control checklist before calling the instructor. Check plumb, level, joint width consistency, bond pattern correctness, joint finish uniformity, and the absence of mortar smears on face stone. If you find a deviation, note it in your written summary along with the corrective action you took or could take. Honest self-assessment is a professional skill that employers value.

Safety Summary

Key terms10

Coursed ashlarA stone wall pattern in which stones are cut or selected so their bed joints form continuous horizontal courses of consistent height across the wall face.
Random rubbleA stone wall pattern using undressed or minimally dressed stones of irregular shape and size, with no continuous horizontal courses but controlled bond.
Bond stoneA stone that runs from the face toward the back of a wall wythe to tie the wythe together and resist splitting; also called a through stone or tie stone.
Type S mortarA mortar mix with high strength and good bond, suitable for exterior, below-grade, and structural masonry applications including stone walls.
Thumbprint-hardThe condition of mortar at which it is firm enough to hold a thumbprint without sticking to the thumb—the correct stage for tooling joints.
Convex jointerA curved metal tool drawn along a mortar joint to compress and finish it with a rounded profile, improving water resistance and appearance.
Head jointThe vertical mortar joint between adjacent masonry units in the same course.
Single-wythe wallA wall that is only one masonry unit thick from face to back.
PlumbPerfectly vertical, as verified with a level or plumb bob; this lab requires plumb within 1/4 inch over the full panel height.
Corner bondThe alternating overlap of stones at a wall corner from course to course, ensuring structural continuity and preventing a straight vertical joint at the corner.

Worked examples4

1. Your coursed ashlar panel is 4 feet (48 inches) long. Your stones are 4 inches tall and you want 1/2-inch bed joints. How many courses do you need to reach at least 4 courses high, and what is the total panel height?
  1. Step 1 – Identify one course height: stone height + one bed joint = 4 in + 0.5 in = 4.5 in.
  2. Step 2 – The first course sits on a mortar bed but the top of the last course has no joint above it in the panel height calculation for this lab, so height = (number of courses × stone height) + (number of bed joints × joint thickness). For 4 courses: bed joints between courses = 3 (between courses 1–2, 2–3, 3–4), plus 1 bed joint under course 1 = 4 bed joints total.
  3. Step 3 – Total height = (4 × 4 in) + (4 × 0.5 in) = 16 in + 2 in = 18 in.
  4. Step 4 – Confirm the lab minimum: 4 courses high is required; 18 inches satisfies that requirement.
Answer: 4 courses produces a panel 18 inches tall, which meets the lab minimum of 4 courses.
2. You are checking level on a 4-foot run of your panel. One end reads 1/4 inch higher than the other end on your 4-foot level. Does the panel pass or fail the lab specification?
  1. Step 1 – State the specification: level within 1/8 inch per 4-foot run.
  2. Step 2 – Compare the measured deviation: 1/4 inch = 0.25 inch.
  3. Step 3 – Compare to tolerance: 0.25 in > 0.125 in (1/8 in).
  4. Step 4 – The deviation exceeds the allowed tolerance.
Answer: The panel fails the level specification. The deviation of 1/4 inch is twice the allowed 1/8 inch tolerance; the course must be corrected before proceeding.
3. Your random rubble wall is 36 inches (3 feet) long. The specification calls for bond stones at least every 3 feet of wall length. How many bond stones are required at minimum along this 36-inch run?
  1. Step 1 – Convert wall length to feet: 36 in ÷ 12 = 3 ft.
  2. Step 2 – Divide wall length by maximum bond stone spacing: 3 ft ÷ 3 ft = 1 interval.
  3. Step 3 – One interval means bond stones are needed at the start and end of that interval. For a 3-foot wall with bond stones at every 3 feet, at minimum one bond stone is required within the span (not counting corner stones, which serve a separate function).
  4. Step 4 – Placing one bond stone at or near mid-wall (approximately 18 inches from each end) satisfies the every-3-foot requirement for this panel.
Answer: At minimum, one bond stone is required along the 36-inch run, placed so no section of wall exceeds 3 feet without a bond stone.
4. You have 10 head joints on a coursed ashlar panel face. After tooling, you measure their widths: eight measure 1/2 inch and two measure 3/4 inch. What is the average head joint width, and are the two wide joints a concern for consistency?
  1. Step 1 – Sum all joint widths: (8 × 0.5 in) + (2 × 0.75 in) = 4.0 in + 1.5 in = 5.5 in.
  2. Step 2 – Calculate the average: 5.5 in ÷ 10 = 0.55 in.
  3. Step 3 – The target joint width is 1/2 inch (0.5 in). The two joints at 3/4 inch are 1/4 inch wider than target—50% over the intended width.
  4. Step 4 – While the average (0.55 in) is close to target, the two outlier joints represent a consistency failure visible on the wall face and must be noted in the self-inspection summary.
Answer: Average joint width is 0.55 inch. The two 3/4-inch joints deviate significantly from the 1/2-inch target and must be documented as inconsistencies in the quality-control summary.

The math in this lesson2

Learners count 4-1/2 in courses to reach 48 in, place bond stones per 3 ft, and average ten head-joint widths.
N-Q.1S-ID.2
Brush up in the math halls at newSchoolWorks.com:
In class: Each student selects stone units from the supply yard, sorting for size and shape compatibility with their assigned pattern (half the class builds coursed ashlar; the other half builds random rubble); students prepare a unit layout sketch before mortar is mixed. · Students construct the full panel in sessions across multiple class days, alternating bond patterns at corners and bond stones at regular intervals, cutting units to fit with wet saw or hand tools as needed, and tooling joints when mortar is thumbprint-hard with a convex jointer. · At completion, students conduct a self-inspection using a program quality-control checklist (plumb, level, joint width consistency, bond pattern, joint finish, absence of mud smears on face stone) and submit a written summary of any deviations from specification and how they were corrected.
Materials: Assorted natural and manufactured stone units, Type S mortar materials, mixing trough, brick and margin trowels, rubber mallet, wet saw, chisel set, mason's hammer, 4-foot level, plumb bob, line blocks and line, convex jointer, sponge, quality-control checklist, student layout sketch paper
Check: Instructor inspection with quality-control checklist: wall plumb within 1/4 inch over full height, level within 1/8 inch per 4-foot run, no open joints, bond stones present at specified intervals, joints tooled uniformly—student must pass all five checklist categories to receive credit for the lab.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NCCER Masonry – Masonry Units and Installation
1. In a coursed ashlar wall, which rule must be followed for head joints in adjacent courses?
NCCER Masonry – Wall Systems and Structural Principles
2. What is the purpose of a bond stone (through stone) in a single-wythe stone wall?
NCCER Masonry – Mortar and Joint Finishing
3. A mason tools joints before the mortar is thumbprint-hard. What is the most likely result?
NCCER Masonry – Mortar Materials and Selection
4. Which mortar type is specified for this lab, and why is it appropriate for an exterior stone wall?
NCCER Masonry – Quality Control and Inspection
5. According to this lab's quality-control specification, a plumb check on a panel 18 inches tall shows the top is 3/8 inch out of plumb. How should the student document this finding?
OSHA 10 – Personal Protective Equipment
6. When using a wet saw to cut stone, which combination of personal protective equipment is required?
NCCER Masonry – Wall Systems and Structural Principles
7. In a random rubble wall, which of the following practices best prevents a structural weakness called a 'continuous vertical joint'?
NCCER Masonry – Masonry Units and Installation
8. A student finishes setting the last course and notices dried mortar smeared on several face stones. What is the preferred time to have removed those smears?
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