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Difficulty: MediumConcrete and Masonry Materials

A mason is constructing a standard concrete masonry unit (CMU) block wall on a cured concrete footing. Arrange the following construction steps in their correct chronological order from first to last.

  1. 1Spread a full mortar bed joint along the chalk line on the concrete footing.
  2. 2Set, level, and plumb the corner lead blocks at each end of the wall.
  3. 3Fasten and tension a mason's line between the corner leads.
  4. 4Butter head joints and lay intermediate stretcher blocks to the guide line.
  5. 5Strike and compact the mortar joints with a jointer once thumbprint hard.

Answer

The correct sequence is: (1) Spread a full mortar bed joint on the footing, (2) Set, level, and plumb corner lead blocks, (3) Fasten and tension a mason's line between the corner leads, (4) Butter head joints and lay intermediate stretcher blocks, and (5) Strike and compact the mortar joints once thumbprint hard.
Constructing a CMU block wall follows a strict trade sequence: first, spreading the mortar bed on the footing provides the base; second, setting and leveling the corner leads establishes height and vertical plumb; third, pulling a taut mason's line provides the horizontal guide; fourth, buttering and laying stretcher blocks completes the course; and fifth, striking joints when thumbprint hard seals the mortar against moisture.

Step-by-Step Solution

1
Spread a continuous bed of mortar along the foundation layout line.
Establishes the bonding layer between the concrete footing and the bottom course of CMU blocks.
The mortar bed cushions and bonds the first masonry course while correcting minor variations in the footing elevation.
2
Position, plumb, and level the corner lead blocks at both wall ends.
Creates fixed structural references for course height, alignment, and vertical plumb.
Corner leads anchor the dimensions of the wall; without precise corners, intermediate blocks cannot be aligned accurately.
3
Attach a taut mason's string line between the corner blocks.
Provides a continuous visual guide for the top outer edge of all intermediate blocks.
The line allows rapid, consistent placement of filler blocks without needing a spirit level on every single unit.
4
Apply mortar to unit flanges (head joints) and set intermediate stretcher blocks to the line.
Completes the solid masonry course with uniform vertical and horizontal joint thickness.
Aligning stretchers directly to the line maintains a straight, true wall plane.
5
Compress and finish the exposed joints using a jointing tool when the mortar reaches thumbprint hardness.
Creates a dense, concave, weather-tight mortar seal that resists water penetration.
Tooling at thumbprint hardness properly compacts the mortar paste against the block edges without smearing wet mix.

Key Concept

Concrete Masonry Unit (CMU) Wall Construction Sequence
Estimated Time:1m 0s
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Topics

Concrete and Masonry Materials

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