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newSchoolWorks.com › VoTechWorks › Building & Construction › Masonry › Brick Masonry: Materials, Bonds, and Coursed Wall Construction › Lesson 3
BLD-MASO04-02 · Lesson 3 · 12 clock hours · lab

Mortar Mixing, Consistency, and Joint Profiles for Brick

Objective. The learner will batch and hand-mix a Type S mortar to correct proportions, assess workability by slump, and produce at least three specified joint profiles (concave, struck, weathered) on a cured sample panel.

⚠ 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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Mortar Mixing, Consistency, and Joint Profiles for Brick

Why Mortar Quality Matters

Mortar is the binding element that holds a masonry wall together and transfers loads evenly from unit to unit. A batch that is too stiff will not bond properly; one that is too wet loses strength and bleeds. Getting the mix right—and then finishing the joint correctly—determines how long the wall lasts and how well it sheds water.

ASTM C270 and Type S Mortar

ASTM C270 is the standard specification that governs mortar for unit masonry. It defines four mix types: M, S, N, and O. Type S is the workhorse mix for below-grade work, exterior walls, and any application where higher bond strength is needed. Under the proportion specification in ASTM C270, a Type S mortar using Portland cement and hydrated lime combines:

If masonry cement labeled Type S is used instead, no additional lime is added; the bag is pre-blended to ASTM C91 requirements. Always check the bag label before batching.

Water is not given a fixed proportion in the standard. You add just enough clean water to reach the correct workability for the conditions of the day—hot, dry weather demands a slightly wetter mix; cool, humid weather needs less.

Volume vs. Weight Batching

Shovel-count (volume) batching is the most common field method. A flat shovel of packed material is not consistent, so the shovel count only works if every loader fills and levels the shovel the same way each batch. It is fast but introduces variation.

Weight batching uses a scale to measure each ingredient in pounds or kilograms. It is more precise and is the preferred method when matching a design mix or troubleshooting strength problems. In today's lab you will compare both methods side-by-side so you can see the difference in consistency.

Testing Workability

Two quick field checks confirm workability:

1. Thumbprint test – Press your thumb firmly into the surface of a fresh trowel load. Correct mortar leaves a clean thumbprint with sharp edges. Mortar that collapses or smears is too wet; mortar that crumbles is too dry.

2. Slump observation – Load the mortar board and observe how it sits. Properly mixed Type S mortar holds a mounded shape on the hawk or board without slumping flat. Some published guides reference a 2½–3½ inch cone slump when tested with a small truncated-cone tool, but the thumbprint test is the most practical daily check on the job.

Mortar that has been sitting more than about 2.5 hours in warm conditions, or has begun to stiffen from hydration (not from evaporation), must be discarded. Retempering (adding water to restore workability) is acceptable only once, and only if the mortar has stiffened due to evaporation—never if it has already begun to set.

Joint Profiles and Their Tools

After the mortar has stiffened enough to hold its shape (thumb-press leaves an impression but does not sink in), you tool the joint. Tooling compresses the mortar against the brick face, improving weathertightness and creating a finished appearance.

| Profile | Tool | Weather Performance |

|---|---|---|

| Concave | Jointing iron (curved) | Excellent – water sheds away from the joint |

| Struck | Margin trowel | Moderate – lower edge is undercut; can trap water |

| Weathered | Flat jointer or margin trowel | Good – upper edge projects slightly, shedding water |

Concave is the most commonly specified profile for exterior work because the compression and shape both resist moisture entry. Struck is a decorative choice, used on interior or sheltered surfaces. Weathered is a traditional profile that still performs well outdoors when executed correctly.

Tool head joints before bed joints. Work in a consistent direction so the tool does not smear mortar back onto a finished surface.

Safety in the Mortar Lab

Key terms10

ASTM C270The standard specification for mortar for unit masonry, published by ASTM International; defines mix types M, S, N, and O by both proportion and property specifications.
Type S mortarAn ASTM C270 mortar type offering high bond strength; proportioned at 1 part Portland cement, ½ part hydrated lime, and 4½ parts masonry sand; used for exterior and below-grade masonry.
WorkabilityThe ease with which fresh mortar can be spread, cut, and bonded to masonry units; affected by water content, mix proportions, and temperature.
Thumbprint testA field check for mortar consistency in which a thumb pressed firmly into fresh mortar should leave a clean, sharp-edged impression; indicates correct water content.
RetemperingAdding water to mortar that has stiffened due to evaporation in order to restore workability; acceptable only once and only when stiffening is caused by water loss, not by hydration setting.
Concave jointA tooled mortar joint with a curved, recessed profile formed by a rounded jointing iron; the preferred exterior joint profile because it sheds water and compresses mortar tightly against the brick.
Struck jointA mortar joint finished with the lower edge cut back and the upper edge flush with the brick face, formed with a margin trowel; can trap water and is better suited to interior or sheltered surfaces.
Weathered jointA mortar joint in which the upper portion is recessed and the lower edge projects slightly, directing water away from the wall face; formed with a flat jointer or margin trowel.
Hydrated limeCalcium hydroxide added to Portland cement mortar to improve plasticity and water retention; used in controlled amounts per ASTM C270.
Volume batchingMeasuring mortar ingredients by shovel count or bucket volume rather than weight; fast but less precise than weight batching.

Worked examples4

1. You need to batch a 4-cubic-foot volume mix of Type S mortar using the Portland cement / hydrated lime / sand proportion specification. How many parts of each ingredient do you need, and what fraction of the total volume does each represent?
  1. Identify the ASTM C270 proportion for Type S: 1 part Portland cement, ½ part hydrated lime, 4½ parts masonry sand.
  2. Add the parts: 1 + 0.5 + 4.5 = 6 total parts.
  3. Each part = 4 cu ft ÷ 6 = 0.667 cu ft.
  4. Portland cement: 1 × 0.667 = 0.667 cu ft.
  5. Hydrated lime: 0.5 × 0.667 = 0.333 cu ft.
  6. Masonry sand: 4.5 × 0.667 = 3.000 cu ft.
  7. Check: 0.667 + 0.333 + 3.000 = 4.000 cu ft ✓
Answer: Portland cement: 0.667 cu ft; hydrated lime: 0.333 cu ft; masonry sand: 3.000 cu ft.
2. Your shovel holds approximately 0.111 cubic feet of material per level scoop. Using the volume amounts from the example above, how many scoops of each ingredient do you need for a 4-cubic-foot Type S batch?
  1. Portland cement needed: 0.667 cu ft. Scoops = 0.667 ÷ 0.111 = 6.0 scoops.
  2. Hydrated lime needed: 0.333 cu ft. Scoops = 0.333 ÷ 0.111 = 3.0 scoops.
  3. Masonry sand needed: 3.000 cu ft. Scoops = 3.000 ÷ 0.111 = 27.0 scoops.
  4. Total scoops: 6 + 3 + 27 = 36 scoops, which equals 36 × 0.111 = 4.0 cu ft ✓
Answer: 6 scoops Portland cement, 3 scoops hydrated lime, 27 scoops masonry sand.
3. A bag of Portland cement weighs 94 lb and has a loose volume of about 1 cubic foot. If you want to batch one part cement by weight for a Type S mix (and one part = 94 lb), what are the target weights for hydrated lime and masonry sand? Assume hydrated lime weighs approximately 40 lb per cubic foot loose and masonry sand weighs approximately 80 lb per cubic foot loose.
  1. One part Portland cement = 94 lb (given).
  2. Hydrated lime ratio = ½ part by volume. Volume of lime needed = 0.5 × 1 cu ft = 0.5 cu ft. Weight = 0.5 × 40 lb = 20 lb.
  3. Masonry sand ratio = 4.5 parts by volume. Volume of sand needed = 4.5 × 1 cu ft = 4.5 cu ft. Weight = 4.5 × 80 lb = 360 lb.
  4. Record: 94 lb cement + 20 lb lime + 360 lb sand = 474 lb total dry ingredients for this batch.
Answer: Hydrated lime: 20 lb; masonry sand: 360 lb; total dry weight: 474 lb.
4. You mixed a batch at 8:00 a.m. on a warm day (85 °F). At what time must you discard the batch if it has not been used, following the common 2.5-hour guideline?
  1. Start time: 8:00 a.m.
  2. Maximum usable life: 2.5 hours.
  3. 2.5 hours = 2 hours 30 minutes.
  4. Discard time: 8:00 a.m. + 2 hours 30 minutes = 10:30 a.m.
Answer: The batch must be discarded by 10:30 a.m.

The math in this lesson2

Learners split a 4 cubic foot Type S batch into parts, convert to shovel scoops, and time a 2.5-hour discard.
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Brush up in the math halls at newSchoolWorks.com:
In class: Instructor demonstration: weigh out Portland cement, masonry cement, hydrated lime, and sand to ASTM C270 Type S proportions; mix in a mechanical mixer, then demonstrate thumbprint workability test and slump consistency; learners record proportions and observations in their lab logs. · Lab rotation: in groups of three, learners batch two 4-cubic-foot mixes—one by volume using a shovel-count method and one by weight—compare consistency, and note differences in their logs. · Practice panel exercise: each learner lays a three-course sample row on a pre-built backing board, then tools joints with a jointing iron (concave), margin trowel (struck), and flat jointer (weathered); instructor evaluates profile depth and uniformity.
Materials: Mechanical mortar mixer, Portland cement, masonry cement Type S, hydrated lime, masonry sand, water, measuring buckets, scale, brick samples (for panel), jointing iron, margin trowel, flat jointer, rubber mallet, level, NCCER Masonry Level 1 module, lab log booklets
Check: Lab log entry checked for correct proportions and recorded observations; joint profiles evaluated by instructor against NCCER rubric—each of three profiles must show uniform depth and smooth finish with no voids; 80% of scored criteria must be met to pass.

Practice check8

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

NCCER Masonry - Materials and Properties
1. According to ASTM C270, which ingredient ratio correctly describes Type S mortar using the proportion specification with Portland cement and hydrated lime?
NCCER Masonry - Tools, Equipment, and Work Practices
2. A mason performs the thumbprint test on fresh mortar and the surface collapses and smears rather than leaving a clean impression. What does this indicate?
NCCER Masonry - Wall Construction
3. Which joint profile provides the best performance on an exterior brick wall exposed to heavy rain, and why?
NCCER Masonry - Materials and Properties
4. When is retempering of mortar acceptable?
OSHA 10 - Personal Protective Equipment
5. Which personal protective equipment is required when dry-handling Portland cement and masonry sand in the mortar lab?
OSHA 10 - Hazard Recognition and Control
6. A mason wants to clear a stone lodged inside a running mortar mixer. What must be done first?
NCCER Masonry - Materials and Properties
7. You batch two Type S mixes: one by shovel count and one by weight. The weight-batched mix is noticeably stiffer. Which explanation is most likely?
NCCER Masonry - Wall Construction
8. In what order should a mason tool joints on a freshly laid brick course?
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