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CMU Control Joint Guide

CMU Control Joint Guide

CMU walls are strong and durable, but concrete masonry structures can still experience:

  • Expansion
  • Contraction
  • Structural movement
  • Temperature stress

Without proper movement control:
masonry walls may develop:

  • Cracks
  • Structural stress
  • Water infiltration problems

This is why:

CMU control joints

are extremely important in masonry construction.

What Is a CMU Control Joint?

A:

CMU control joint

is a vertical separation designed to control cracking in concrete masonry walls.

Control joints allow masonry walls to:

  • Move slightly
  • Relieve stress
  • Reduce cracking
  • Handle thermal movement

These joints help direct cracking into controlled locations instead of random wall areas.

Control joints are commonly used in:

  • Commercial buildings
  • Residential walls
  • Retaining walls
  • Long masonry walls
  • Structural masonry systems

Purpose of Control Joints in CMU Walls

The main purpose of:

control joints

is to reduce stress caused by:

  • Temperature changes
  • Moisture movement
  • Concrete shrinkage
  • Structural movement

Concrete masonry naturally expands and contracts over time.

Without movement joints:
pressure may build inside the wall, leading to:

  • Cracking
  • Masonry separation
  • Structural damage

How CMU Control Joints Work

Control joints create intentional separation points inside masonry walls.

These joints:

  • Allow controlled movement
  • Reduce stress concentration
  • Prevent random cracking

Special joint materials are usually installed to:

  • Seal the opening
  • Prevent water infiltration
  • Maintain flexibility

Where Are CMU Control Joints Installed?

Control joints are commonly installed:

  • At wall intervals
  • Near corners
  • Around openings
  • At changes in wall height
  • Near structural transitions

They are especially important in:

  • Long masonry walls
  • Exterior walls
  • Reinforced masonry systems

Recommended Control Joint Spacing

Control joint spacing depends on:

  • Wall length
  • Wall height
  • Reinforcement
  • Climate conditions
  • Building design

Typical spacing recommendations include:

Wall TypeTypical Joint Spacing
Exterior CMU walls20–25 feet
Interior CMU walls25–30 feet
Reinforced masonry wallsBased on engineering design

Actual spacing should follow:

  • Structural engineering requirements
  • Local building codes
  • Masonry standards

CMU Control Joint vs Expansion Joint

Many people confuse:

control joints

with:

expansion joints

However:
they serve different purposes.

FeatureControl JointExpansion Joint
Main PurposeControl crackingAllow expansion
Common UseCMU masonry wallsLarge structures
Movement TypeShrinkage controlExpansion movement
Typical DirectionVerticalVertical or horizontal

Control joints mainly help manage:

shrinkage cracking

while expansion joints allow larger structural movement.

Why CMU Walls Crack

Concrete masonry walls may crack because of:

  • Temperature changes
  • Drying shrinkage
  • Foundation movement
  • Structural loads
  • Wind pressure
  • Seismic activity

Properly designed control joints help minimize visible cracking.

Control Joint Materials

Control joints often include:

  • Flexible sealants
  • Backer rods
  • Joint fillers
  • Waterproof materials

These materials help:

  • Maintain flexibility
  • Prevent moisture penetration
  • Improve wall durability

Reinforced Masonry and Control Joints

Reinforced masonry systems may still require:

control joints

even when:

  • Rebar reinforcement
  • Bond beam systems
  • Grouted cells

are used.

Reinforcement improves structural strength, but movement control remains important.

You can also read:

What Is a Bond Beam Block?

Control Joints and Wall Height

Tall masonry walls usually require:

  • More movement control
  • Proper reinforcement
  • Engineered joint spacing

You can also read:

How Tall Can a CMU Wall Be?

CMU Wall Thickness and Control Joints

Wall thickness may affect:

  • Joint spacing
  • Reinforcement requirements
  • Structural movement

Common CMU wall thicknesses include:

  • 4 inch
  • 6 inch
  • 8 inch
  • 12 inch

You can also read:

<a href="/cmu-wall-thickness-guide/">CMU Wall Thickness Guide</a>

Common Uses of Control Joints

CMU control joints are commonly used in:

  • Commercial masonry walls
  • Residential block walls
  • Retaining walls
  • School buildings
  • Warehouses
  • Industrial masonry systems

They are especially important for:

  • Long wall spans
  • Exterior walls
  • Reinforced masonry construction

Advantages of CMU Control Joints

1. Reduces Cracking

Control joints help reduce:

  • Random cracking
  • Stress fractures
  • Masonry separation

2. Improves Wall Durability

Movement control improves:

  • Long-term wall performance
  • Structural stability
  • Masonry lifespan

3. Improves Moisture Protection

Proper joint sealing helps reduce:

  • Water infiltration
  • Moisture damage
  • Freeze-thaw deterioration

4. Improves Structural Performance

Control joints help masonry walls better handle:

  • Thermal movement
  • Structural stress
  • Wind pressure

CMU Control Joints and Building Codes

Many building codes require:

control joints

for certain masonry wall applications.

Structural engineers determine:

  • Joint placement
  • Spacing requirements
  • Reinforcement details

based on:

  • Wall design
  • Climate conditions
  • Structural loads

Use a CMU Block Calculator

Before building a masonry wall, accurate material estimation is important.

Our:

CMU Block Calculator

helps estimate:

  • Concrete block quantities
  • Mortar requirements
  • Material costs
  • Wall dimensions

You can also use:

for additional construction estimation.

Frequently Asked Questions

What is a CMU control joint?

A CMU control joint is a vertical separation designed to:

  • Control cracking
  • Relieve stress
  • Allow wall movement

in masonry walls.

Why are control joints important?

Control joints help reduce:

  • Random wall cracking
  • Structural stress
  • Moisture damage

caused by masonry movement.

How far apart should control joints be?

Typical spacing ranges from:

20 to 30 feet

depending on:

  • Wall type
  • Reinforcement
  • Structural design
  • Local codes

Are control joints required in reinforced masonry walls?

Yes.
Reinforced masonry walls may still require:

movement control joints

to manage thermal and shrinkage movement.

Related Articles

Final Thoughts

CMU control joints are an essential part of masonry wall construction because they help:

  • Reduce cracking
  • Relieve structural stress
  • Improve wall durability
  • Control masonry movement

Properly designed movement joints improve the long-term performance of:

  • Residential walls
  • Commercial masonry systems
  • Reinforced structural walls

Understanding control joints helps contractors, engineers, builders, and homeowners construct stronger and more durable masonry wall systems.