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newSchoolWorks.com › VoTechWorks › Building & Construction › Masonry › Masonry Capstone: Integrated Build Project › Lesson 3
BLD-MASO04-11 · Lesson 3 · 72 clock hours · practice

Masonry Wall Construction: Block Backup, Veneer, and Arch

Objective. Students lay the concrete masonry unit backup wythe, apply metal ties, set brick or stone veneer facing, and form and lay a rowlock or jack arch to NCCER plumb, level, and alignment tolerances while maintaining a complete daily field log.

⚠ 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.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Masonry Wall Construction: Block Backup, Veneer, and Arch

This capstone practice session brings together every core skill you have built: laying concrete masonry units (CMU), setting a veneer wythe with a proper air space, installing wall ties, and forming and laying an arch. Work carefully, document everything, and hold NCCER tolerances on every course.

The CMU Backup Wythe

The backup wythe is the structural spine of a cavity wall. Begin at the footing by snapping chalk lines to establish the wall face. Mix Type S mortar to a stiff, workable consistency — bed joints should support a unit without slumping. Set a full mortar bed for the first course, furrow it lightly with the trowel tip to ensure full coverage, and lay 8×8×16 CMU units to the line.

Use your story pole to govern every course. The story pole is a straight rod marked at every course height (for standard 8-in. CMU, each mark is 8 in., accounting for a 3/8-in. bed joint and 7-5/8-in. unit). Hold the pole plumb against the wall face; the top of each course must align within 1/8 in. of its mark. Check plumb with a 4-ft level every three courses — do not wait until the wall is tall to find a lean. NCCER tolerance is 1/4 in. per 10 ft of height.

Bed and head joints must be 3/8 in. ± 1/8 in. Use a margin trowel to butter head joints fully before placing each unit. Tap units level and plumb with the handle of your brick trowel. Remove excess mortar with the trowel and return it to the board.

Installing Corrugated Metal Wall Ties

Wall ties transfer lateral loads between the backup and veneer wythes and keep the two together if the wall shifts. Install corrugated metal ties at the spacing specified in the project design. Stagger tie courses so ties in one course do not align vertically with ties in the next. Embed ties at least 1-1/2 in. into both bed joints — backup and veneer. Never bend a tie sharply; a gentle drip-leg slope toward the outer wythe allows any moisture that enters the cavity to drain away from the backup.

The Brick or Stone Veneer Wythe

The veneer carries no floor load; its job is weather protection and appearance. A 1-in. clear air space between the back face of the veneer and the front face of the backup is required. Use a story pole spacer block cut to exactly 1 in. to check the air space at each tie course. Never allow mortar droppings to bridge the air space — bridge mortar creates a moisture path. Keep the cavity clean by dragging a board on edge through the cavity as you go up, or use a foam rope cavity protector.

Match coursing marks on the story pole. Modular brick courses at 2-2/3 in. per course (three courses = 8 in.), which ties to CMU coursing neatly. Tool all exposed joints with a jointer when the mortar reaches thumbprint hardness — you can press your thumb into the surface and leave a clean print without mortar sticking to your skin. Tooling too early smears the unit face; tooling too late tears the joint. A concave jointer is standard unless the design calls for a different profile.

Photograph each completed lift before starting the next. Note the course number and date in the photo caption and in your field log.

Forming and Laying the Arch

An arch transfers load around an opening by converting it to compression in each unit. The two main types you will work with here are the rowlock arch (brick laid on edge in a curved course) and the jack arch (a flat or nearly flat arch using tapered units or tapered joints).

Centering is the temporary plywood formwork that supports arch units while mortar cures. Cut the centering to the specified rise-to-span ratio and verify symmetry before any mortar is mixed. Do a dry bond — lay all arch units on the centering without mortar to check joint taper and unit spacing. Joint taper must be consistent from springer to keystone; adjust unit spacing to achieve even taper on both sides.

When dry bond is correct, remove and mortar from one springer, work both sides simultaneously toward the center, and set the keystone last. The keystone is the top-center unit. Tap it lightly with the trowel handle to seat it; heavy blows crack mortar in the adjacent joints. Allow mortar to reach initial set before striking the centering. Inspect the soffit — the underside of the arch — with a straightedge. NCCER tolerance is flush within 1/4 in. across the span.

Field Log Requirements

A dated entry is required for every work session. Record: date, session hours, mortar batch weights (cement, lime or masonry cement, sand, water), any adjustments made to the mix, number of courses completed, tie locations, and photo reference numbers. The field log is a pass/fail item — an incomplete log means this lesson is not complete, regardless of how well the wall is built.

Safety

Silica dust from cutting CMU or brick causes silicosis, a permanent lung disease. Wear an N95 or half-face respirator rated for silica any time you cut, grind, or rake masonry. Use a wet-cut angle grinder or one with dust collection; never dry-cut indoors. Connect all power tools to a GFCI-protected circuit. Wear safety glasses, hard hat, steel-toed boots, and gloves at all times. Use hearing protection when cutting. Before any tool service or blade change, follow lockout/tagout procedures: de-energize, lock out, tag out, and verify zero energy before touching the blade or disc.

Key terms10

Backup wytheThe inner, structural leaf of a cavity wall, typically built of CMU, that carries floor and roof loads and anchors the veneer.
Veneer wytheThe outer, non-load-bearing leaf of a cavity wall, usually brick or stone, that provides weather protection and finished appearance.
Story poleA straight rod marked at every course height used to keep all courses at uniform elevation across the full width of a wall.
Corrugated metal wall tieA stamped or corrugated metal strip embedded in bed joints of both wythes to transfer lateral loads and tie them together across the air space.
CenteringTemporary plywood formwork cut to the arch profile that supports arch units until mortar achieves sufficient strength to be self-supporting.
KeystoneThe central unit at the crown of an arch, set last, that locks the arch in compression and completes the structure.
Thumbprint hardnessThe curing stage at which a thumb pressed into the mortar joint leaves a clean impression without mortar sticking — the correct time to tool joints.
Air space (cavity)The clear gap — typically 1 in. minimum — between the back face of the veneer and the front face of the backup wythe that controls moisture infiltration.
SoffitThe exposed underside surface of an arch or beam, inspected for alignment and joint closure after centering is removed.
Dry bondLaying arch or course units without mortar to verify spacing, joint taper, and symmetry before committing to the final mortar placement.

Worked examples4

1. Your story pole is marked for standard modular CMU coursing. Each CMU is 7-5/8 in. tall and the bed joint is 3/8 in. At what height should the top of the 5th course appear on the story pole?
  1. Nominal course height = unit height + bed joint = 7-5/8 in. + 3/8 in. = 8 in. per course.
  2. Height at top of 5th course = 5 × 8 in. = 40 in.
Answer: The top of the 5th CMU course should read 40 in. on the story pole.
2. You measure a bed joint and find it is 5/8 in. thick. Is it within the NCCER tolerance of 3/8 in. ± 1/8 in.? By how much does it deviate?
  1. NCCER tolerance range: 3/8 in. − 1/8 in. = 2/8 in. (1/4 in.) minimum; 3/8 in. + 1/8 in. = 4/8 in. (1/2 in.) maximum.
  2. Measured joint = 5/8 in. = 0.625 in.; maximum allowed = 4/8 in. = 0.500 in.
  3. Deviation above maximum = 5/8 in. − 4/8 in. = 1/8 in. over tolerance.
Answer: The 5/8-in. joint is out of tolerance by 1/8 in. over the maximum allowed 1/2 in. It must be corrected.
3. A jack arch spans 36 in. between springings. You are using 10 brick units plus 1 keystone (11 units total) with a uniform tapered joint. The mortar head joints must taper from a minimum of 1/4 in. at the soffit to a maximum at the extrados. If the units are 3-5/8 in. wide, what total masonry width (units only, no joints) must fit within the 36-in. span?
  1. Total unit width = number of units × unit width = 11 × 3-5/8 in. = 11 × 3.625 in. = 39.875 in.
  2. Space remaining for joints = span − total unit width = 36 in. − 39.875 in. = −3.875 in.
  3. The negative result means 11 full-width units do not fit in a 36-in. span without cutting. You need to either use fewer units, cut some units, or use units with a smaller bed width. This dry-bond check reveals the problem before any mortar is placed.
Answer: Eleven standard 3-5/8-in. units exceed the 36-in. span by about 3-7/8 in. The dry bond shows units must be cut or the unit count reduced — exactly why a dry bond is required before mortaring.
4. You are checking wall plumb on a CMU backup wythe that is 7 ft 6 in. (90 in.) tall. NCCER allows 1/4 in. deviation per 10 ft. What is the maximum allowable out-of-plumb deviation for this wall height?
  1. Convert wall height to feet: 90 in. ÷ 12 = 7.5 ft.
  2. Allowable deviation = (1/4 in. per 10 ft) × 7.5 ft = 0.25 × 0.75 = 0.1875 in.
  3. Round to the nearest practical fraction: 0.1875 in. ≈ 3/16 in.
Answer: The maximum allowable out-of-plumb for a 7 ft 6 in. wall is approximately 3/16 in.

The math in this lesson2

Learners compute CMU course heights, joint deviation, jack-arch joint spacing, and plumb allowance of 1/4 in per 10 ft.
6.RP.3N-Q.1
Brush up in the math halls at newSchoolWorks.com:
In class: Lay the CMU backup wythe from the footing to full height, using a story pole to maintain consistent coursing, checking plumb every three courses with a 4-ft level, and keeping bed and head joints at 3/8 in. ± 1/8 in.; install corrugated metal wall ties at spacing required by the project design, staggering courses; record mortar batch weights and any adjustments in the field log each session. · Lay the brick or stone veneer wythe with a consistent 1-in. air space maintained by a story pole spacer block, matching the coursing established on the backup wythe; tool all exposed joints with a jointer when mortar reaches thumbprint hardness; photograph each completed lift and annotate photos in the portfolio with course number and date. · Build temporary arch formwork (centering) from plywood to the specified rise-to-span ratio; dry-bond arch units to check joint taper symmetry; lay arch units in mortar from both springings toward the keystone simultaneously, setting the keystone last and lightly tapping to seat; remove centering after mortar achieves initial set and inspect the soffit for alignment and joint closure.
Materials: Concrete masonry units (8x8x16 standard), modular brick or stone units, Type S mortar (bagged or site-batched), mortar box or electric mixer, trowels (brick and margin), story pole, 4-ft and 2-ft levels, plumb bob, line blocks and mason's line, joint raker and jointer, corrugated metal wall ties, plywood for arch centering, arch form template, hammer, bolster chisel, angle grinder with diamond blade (wet-cut or with dust collection), GFCI-protected extension cord, PPE (hard hat, safety glasses, N95 or half-face respirator for silica dust, gloves, steel-toed boots, hearing protection for cutting), field log, camera
Check: Instructor uses a straightedge and level to verify: wall plumb within 1/4 in. per 10 ft of height; coursing height within 1/8 in. of story pole marks across full width; head and bed joints 3/8 in. ± 1/8 in.; arch soffit flush within 1/4 in. across span. Field log must have a dated entry for every work session with mortar batch data and photo numbers. All tolerances must be met and log complete to pass this lesson.

Practice check8

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

NCCER Masonry — Cavity Wall Construction
1. What is the purpose of maintaining a 1-in. air space between the backup wythe and the veneer wythe?
NCCER Masonry — Wall Ties and Anchors
2. When installing corrugated metal wall ties, why should tie courses be staggered rather than aligned vertically?
NCCER Masonry — Mortar Joint Finishing
3. You press your thumb into a mortar joint and mortar sticks to your thumb and smears the brick face. What does this indicate about joint tooling timing?
NCCER Masonry — Quality and Tolerances
4. According to NCCER masonry tolerances, a wall 10 ft tall must be plumb within:
NCCER Masonry — Arch Construction
5. What is the correct sequence for laying arch units once centering is in place and the dry bond is verified?
NCCER Masonry — Documentation and Professionalism
6. A field log entry is missing mortar batch data for one session. Under the pass/fail criteria for this lesson, what happens?
OSHA 10 — Silica and Respiratory Hazards
7. Which respiratory protection is required when cutting CMU with an angle grinder?
OSHA 10 — Lockout/Tagout
8. Before changing the diamond blade on an angle grinder during the arch-cutting phase, what procedure must be followed?
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