How to Mix Mortar Correctly

Why Proper Mortar Mixing Matters

Mortar has to hold the wall together and stay workable long enough to use. Too wet or too weak and the joints suffer. Pick the right mix, then dial in the consistency.

Understanding Mortar Types

ASTM Mortar Classifications

Type	Strength (PSI)	Best Uses
M	2,500+	Below-grade, foundations, retaining walls
S	1,800+	Structural walls, high wind/seismic areas
N	750+	General purpose, above-grade walls
O	350+	Non-load-bearing, interior walls
K	75+	Historic restoration, soft brick

When to Use Each Type

Type N (Most Common)

• Residential brick veneer
• Chimneys above roofline
• Interior partitions
• Moderate load applications

Type S (Strong)

• Foundation walls
• Below-grade masonry
• High-wind regions
• Structural reinforced walls

Type M (Maximum)

• Retaining walls
• Below-grade applications
• Severe frost exposure
• Heavy load-bearing

Pro tip: When in doubt, use Type S. It’s overkill for most residential but won’t cause problems. Using too weak a mortar is the real mistake.

Mortar Components

Portland Cement

• Provides strength
• Type I or II for most applications
• Never use “plastic cement” (has additives)

Lime

• Improves workability
• Increases bond strength
• Adds flexibility (reduces cracking)
• Helps retain water during curing

Sand

• Provides bulk and texture
• Must be clean, well-graded
• Masonry sand (fine) preferred
• Never use beach sand (salt content)

Water

• Clean, potable water only
• Temperature affects set time
• Most critical variable in mixing

Pre-Mixed vs. Job-Mixed Mortar

Pre-Mixed Bags (Type S, N)

Pros:

• Consistent proportions
• Convenient for small jobs
• No measuring required

Cons:

• More expensive per unit
• Less control over workability
• May have additives

Best for: DIYers, small projects, repairs

Job-Mixed (Custom Proportions)

Pros:

• Lower material cost
• Adjustable for conditions
• Better for large quantities

Cons:

• Requires accurate measuring
• More knowledge needed
• Potential for errors

Best for: Professionals, large projects

Standard Mix Proportions

Type N (General Purpose)

1 part Portland cement
1 part lime
6 parts sand

Type S (Structural)

1 part Portland cement
1/2 part lime
4.5 parts sand

Type M (Heavy Duty)

1 part Portland cement
1/4 part lime
3.5 parts sand

Measuring: Use consistent containers. A 5-gallon bucket works well.

Step-by-Step Mixing Process

Equipment Needed

• Mortar mixer (rental) or wheelbarrow
• Mixing hoe or drill with paddle
• 5-gallon buckets for measuring
• Water source with hose
• Mortar board or hawk
• Clean sponge

Method 1: Mortar Mixer (Best for Large Jobs)

1. Add most of the water (about 2/3 of total)
2. Add half the sand while mixer runs
3. Add all cement and lime
4. Add remaining sand
5. Mix 3-5 minutes - no dry pockets
6. Add remaining water gradually
7. Mix until proper consistency (2-3 more minutes)

Method 2: Wheelbarrow/Hand Mixing

1. Dry mix first - Blend cement, lime, sand
2. Form a crater in center of dry mix
3. Add half the water to crater
4. Fold dry material into water from edges
5. Continue adding water gradually
6. Mix thoroughly - 10+ minutes by hand
7. Check consistency before using

Method 3: Pre-Mixed Bags

1. Empty bag into mixer or wheelbarrow
2. Add water gradually (see package directions)
3. Mix until uniform consistency
4. Let stand 5 minutes (slaking)
5. Remix briefly before use

The Perfect Consistency

Visual Indicators

• Smooth, creamy texture (like peanut butter)
• No dry lumps or pockets
• Holds shape when peaked with trowel
• Slides off trowel when shaken gently

The “Thumb” Test

1. Press thumb into mortar
2. Lift straight up
3. Mortar should stick briefly, then release
4. Impression should hold shape

The “Trowel” Test

1. Load trowel with mortar
2. Turn trowel upside down
3. Mortar should stick for 2-3 seconds
4. Should fall cleanly when shaken

What Wrong Looks Like

Too wet:

• Runny, slumps immediately
• Squishes out of joints
• Weak when cured
• Fix: Add more dry mix sparingly

Too dry:

• Crumbly, falls apart
• Won’t stick to units
• Poor bond strength
• Fix: Add small amounts of water

Not mixed enough:

• Visible dry pockets
• Inconsistent color
• Variable strength
• Fix: Continue mixing 2-3 more minutes

Working Time and Retemper

Working Time (Pot Life)

• Normal conditions: 2-2.5 hours
• Hot weather (above 90°F): 1-1.5 hours
• Cold weather (below 40°F): 3-4 hours

Retempering (Adding Water)

As mortar stiffens from evaporation, you can add small amounts of water:

Acceptable:

• Within first 2.5 hours
• Small water additions only
• Remix thoroughly
• Once or twice maximum

Not acceptable:

• After initial set begins
• Large water additions
• Multiple retemperings
• Mortar that’s been standing 3+ hours

Rule: Never retemper mortar that’s begun to set. Discard it.

Calculating Mortar Quantities

Coverage Per Bag (80 lb)

Application	Coverage
Standard brick	30-35 bricks
Modular brick	40-50 bricks
8” concrete block	12-15 blocks
12” concrete block	8-10 blocks
Stone veneer	8-12 sq ft

Formula for Job-Mixed Mortar

Cubic feet of mortar = (sq ft of wall × joint thickness × 2) ÷ 144

Use our Masonry Calculator for accurate estimates.

Weather Considerations

Hot Weather (above 90°F)

• Mix smaller batches
• Keep materials shaded
• Dampen bricks before laying
• Work faster
• Mist finished joints

Cold Weather (below 40°F)

• Heat mixing water (not over 160°F)
• Use heated sand
• Cover work overnight
• Consider accelerators
• Never lay on frozen surfaces

Rain

• Don’t mix mortar in rain
• Cover fresh work immediately
• Don’t resume until surfaces dry
• Check joints next day

Colored Mortar

Adding Pigments

• Use mortar-specific pigments only
• Maximum 10% of cement weight
• Add pigment to dry mix before water
• Mix thoroughly for uniform color
• Keep batches consistent

Color Matching Tips

• Make test samples first
• Let samples cure 28 days to see true color
• Wet mortar is always darker than cured
• Buy all pigment from same batch

Common Mistakes and Solutions

Mistake	Problem	Solution
Too much water	Weak, porous joints	Measure water carefully
Not enough mixing	Inconsistent strength	Mix minimum 5 minutes
Wrong mortar type	Cracks or too hard	Match to application
Dirty sand	Poor bond	Use clean masonry sand
Using old cement	Reduced strength	Check bag date, store dry
Retempering set mortar	Joint failure	Discard after 2.5 hours

Troubleshooting Mortar Problems

Joints Cracking

Causes:

• Mortar too strong for brick
• Insufficient curing
• Structure settling

Fix: Use softer mortar type, ensure proper curing

Efflorescence (White Staining)

Causes:

• Water migration through masonry
• Salt content in materials

Fix: Improve drainage, use low-alkali cement

Poor Bond (Bricks Falling Off)

Causes:

• Dusty brick surfaces
• Mortar too dry
• Temperature extremes

Fix: Dampen bricks, proper consistency, weather protection

Discoloration

Causes:

• Inconsistent batches
• Varying water content
• Different sand sources

Fix: Consistent measuring, same material sources

Mortar Storage Tips

Unopened Bags

• Store off ground on pallets
• Keep dry - no moisture exposure
• Use within 6 months
• First in, first out

Mixed Mortar

• Use within 2.5 hours
• Don’t store overnight
• Cover with damp burlap while working
• Never freeze

Calculate Your Masonry Materials

Need exact material numbers? Use these calculators:

• Masonry Calculator - For brick and block walls
• Concrete Block Calculator - For CMU walls

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Pro Tip: Keep a simple mixing log for each job. Note the water amount, weather, and result. That makes it easier to repeat a good batch and avoid the same mistake twice.