The "Interlock" in Interlocking Brick Pavers

High Density Concrete Paving Stones were developed to achieve proper Interlock

Brick pavers made from high density concrete have been a popular paving option for almost 35 years in the United States.  Pavers were first widely used as walkways or paths.  They quickly evolved into functional and aesthetically pleasing patios.  As pavers have matured in the market place, the use of residential driveways and municipal city scapes & parks have grown exponentially.

Today, I am still amazed how many homeowners and even contractors, do not understand how interlocking brick pavers work.  Often I go on estimates where homeowners do not believe they actually have interlocking brick pavers, when in fact they do.

 Most homeowners believe that the only interlocking brick paver is the one that are key shaped or has several angled sides.  They believe that they lock together like a jig saw puzzle piece. The most popular shape for brick paver installations is the traditional 4" by 8" rectangle shape.  Laid in a herringbone pattern offers the best performing interlock or lock-up.

The simple truth is that the "Interlocking"of brick pavers is achieved by the method they are installed.  Below is a definition of "Interlock" described by the Intelocking Concrete Pavement Institute (ICPI):

"Frictional forces between paving units that prevent them from rotating, or moving horizontally or vertically in relation to each other, also defined as the inability of a concrete paver to move independently of it neighbors.  The friction forces enable load transfer among the paving units." 

 "The three kinds of load transfer are vertical interlock, horizontal interlock, and rotational interlock.  Vertical interlock is achieved by shear transfer of loads to surrounding units through sand in the joints. Horizontal interlock is primarily achieved through the use of laying patterns that disperse forces from braking and accelerating vehicles.  Rotational interlock  is maintained by the pavers being of sufficient thickness & density, placed closely together, and being restrained by a stationary edge restraint on the borders."

  To achieve the above  interlock or lock-up needed for a high performing paving stone pavement, the method of installing brick pavers is essential. It is the installation process that achieves interlock. Without boring you with all the minor installation details, below explains how we accomplish the three "Interlock" load transfers with brick pavers.

First you install a compacted crushed stone base to the proper specifications recommended  for the particular paver installation  (patio, walk, driveway, etc..).  A strong base will aid in Vertical interlock by transfering "load" back to the paver units.  A strong base will keep the paver units from settling or sinking into the ground and allow the paver units to spread the load between them.

Second you install a sand bedding or leveling course by spreading it over the compacted base approx. 1-1.5" thick.  You will then "screed" (level) the bedding course with the proper heights & pitch that is needed for the final product. You will then lay the paver units over the bedding course in the design & laying pattern determined. After all cut ins are complete and the edge restraint is installed, joint sand will be swept into the joints.

Then the most important step in installing brick pavers will be performed.  You will run the power plate compactor over the paver units in several passes and angles.  Here is where Horizontal interlock occurs.  As the power plate compactor runs over the pavers units, if vibrates several pavers down at the same time.  As the paver units are pushed down into the bedding course..."Jet up" or lock-up of the pavers will occur.  This locks the brick pavers horizontally keeping them from shifting side-to-side.


The final step is to finish sweep all the paver joints with more joint sand.  Rotational interlock is accomplished by butting pavers up to each other, not leaving an excessive gap between each paver units.  This will avoid any "rocking" back and forth of an individual paver unit.  It is also accomplished in the planning stage of selecting the proper thickness, laying pattern, and density of pavers. Specifying the proper paver unit , design, & laying pattern for the particular application is essential.

In summary, the shape of your brick paver unit does not exclude it from the interlocking brick paver application.  The methods of installation will allow any shape or composition (clay, concrete, rubber, asphalt) of pavers to "interlock" into place.

Brick Pavers gaining recognition by Pavement Industry

Interlocking pavers were once seen as a luxury item but now are a viable pavement solution

Interlocking brick pavers are becoming an increasingly viable & economical solution for residential, commercial, and municipal applications.  When properly designed & installed, interlocking concrete pavers will not only offer aesthetically pleasing appearance but offer substantially reduced long-term maintenance & replacement costs compared to poured concrete & asphalt.

These advantages that brick pavers offer have gained recognition throughout the pavement industry in the United States.  With almost 60 years of experience & feedback from Europe, Australia, & Canada, the interlocking paving stone's structural integrity, shapes, colors, textures, and permeability have greatly improved.  Education for architects, engineers, manufacturers, contractors, and the general public have contributed to the proper applications, designs, and installation techniques that best offers long-term success & performance.

The Interlocking Concrete Pavement Institue (ICPI) released an article in their February 2012 magazine that states the American Society for Testing and Materials (ASTM) International has approved a new standard practice for rating the condition of interlocking concrete pavements.  The ASTM International develops international standards for materials, products, systems and services used in construction, manufacturing, and transportation.  Their guidelines are strictly used by the brick paver industry to insure maximum performance.


ASTM E2840-11 was added to an existing rating method known as the Pavement Condition Index (PCI) used for evaluating existing concrete & asphalt pavement conditions.  The ICPI was the driving force that proposed including interlocking concrete pavers for pavement management & data.  

ASTM E2840-11 provides private & commercial project owners and municipalities specific guidance for required maintenance needs & costs and rating severity of current conditions & distresses.  It is amazing how over the last 30 years, so many city street scape projects extensively used interlocking brick pavers but have left them for dead due to lack of maintenance & neglect.


One of the best advantages of including interlocking brick pavers into the PCI rating system with poured concrete & asphalt is that now a more accurate comparison can be made between these alternative pavements.  Evaluating long-term performance &  maintenance costs will especially help municipalities for future projects.  It will also help guide in setting maintenance budgets and schedules.


It is very important that the public is aware that there are standards set in the brick paver & modular retaining wall industry.  There needs to be minimum requirements for products, designs, base materials, and installation techniques to insure long-term success and satisfaction for any paving stone project.  Too often, inexperienced or uneducated contractors install paver patios, walkways, driveways, etc... that only result in failure and client frustration.

Interlocking brick pavers are gaining more and more momentum in the pavement industry.  In the past it was considered a luxury item because of the upfront higher cost versus  poured concrete & asphalt.  Stamped concrete cost is usually the same or more than interlocking brick pavers.  But when you factor in long-term maintenance & replacement costs, interlocking brick pavers are the most economical solution by far. When you factor in the flexibility of designs, colors, textures, and function, there is no comparison either!