We use moveable joints to protect brick and mortar from movement and stress.
All building materials change in volume in response to variations in temperature or moisture content. All structural members deform under load; some also experience time-dependent and/or permanent deformations.
Brick and Mortar has little elasticity. If brick and mortar moves, if the building structure moves and stresses brick masonry, it will crack. We use expansion and control joints to isolate movement in bricks in these moveable joints, and, thereby, reduce the stress in the brick and mortar.
In this section we describe control and expansion joints in greater detail. If you missed our information on the forces which cause building materials, including brick and mortar- you will find that information here.
A brief explanation for clarity – the Difference between Expansion joints & Control Joints
As we have mentioned elsewhere, expansion joints and control joints are built exactly the same, the name can change for the type of brick and mortar cracking stress involved.
Settlement cracks caused by elastic deformation in the structure are dealt with where they are needed with a control joint, and expansion joints are put around cracks caused by moisture absorption where differential expansion rates and constraint of the brick expansion has created brick and mortar cracks.
A system of movement joints can reduce the potential for cracks and the problems they cause.
Restraint of these movements of building materials can cause stresses within brick and mortar that result in cracks. To avoid cracks, masonry elements should be designed to minimize movement or accommodate differential movement between materials and assemblies. In brick masonry, this is accomplished by designing and inserting expansion joints. Estimating the magnitude of the different movements that occur in masonry and other building materials is useful in determining the size and spacing of expansion joints needed to accommodate movement.
In a separate document, we discuss, in depth, the proper design of masonry structures to accommodate brick and mortar movement. But your home is built and you and Brick Doctor as your chosen brick repair contractor, have to live with the existing design of your home and deal practically with how your home is dealing with brick and mortar movement.
Anatomy of Creating an Effective Expansion Joint
Proper elasticity of the elastomeric sealant placed in the control joint demands careful attention to the placement of the backer rod- a non bonding surface which provides an hourglass shape and acts as a bond breaker. Let’s explore these issues in the diagram below.
If your mason does not work with precision and care with the dimensions while making your expansion joint, you could experience early failure and frustration.
Brick Doctor Sees Many Errors in Expansion and Control Joint Preparation.
This expansion joint was poorly sealed with the improper selection of a sealant and the poor application of that sealant. Other images show the cleaning of the joint, the application of the backer rod, the priming of the brick and the final application of elastomeric sealant.
If the joint is not properly cut out and evacuated of mortar and brick material, the two wall sections will still be connected and the expansion in the wall will continue to accumulate along its length and continue concentrating stress which can create potential new cracking problems.
In a “healthy” expansion joint which is more than five years old, the caulk should appear to be compressed or extruded. A pristine expansion joint of this age may indicate the bricklayer did not clean all of the mortar droppings and extrusions out of the joint prior to its being caulked. This is most prevalent at window sills, where the joint was not left open all the way up to the window frame.
The precise fit of the back rod, and the careful preparation of the brick surface on either side of the bond, ensures that proper adhesion of the sealant to the brick is achieved.
The narrow section of cured sealant over the backer rod is where brick movement is absorbed. This center section needs to be optimally flexible. As the wall moves, the elastomeric over the backer rod absorbs movement and the bond to either brick face stays securely adhered.
This composite image of the construction of a expansion joint shows the original crack, cutting out the broken brick and mortar and the finished expansion joint. Please pardon the scaffolding in the picture. These images were caught during the construction process, obviously. 
Proper tooling of the elastomeric is also critical. Make sure your brick repair contractor has years of experience and expertise and patience to make sure this is done right. The quality is built in.
This effort is non trivial and the depth of the backer rod and the proper fit in the cut brick channel properly match up to create this long lasting hourglass shape.
Related:
The Fundamentals of Brick and Mortar Repair
What causes Brick and Mortar to Crack and What Can You do about It?
Brick Doctor is Ready to Help with your Questions and Concerns about installing Flexible Joints in Brick
Over the years, Brick Doctor has done just about everything when it comes to relieving stress in brick and mortar with flexible joints. We know what we are doing. Let us know if we can help you.
Don’t take our word for it. (Check out our testimonials and reviews). And, even better, ask a neighbor for a recommendation. We have done tens of thousands of projects all over the DFW Metroplex since 1986, including for some of your neighbors.
Have any particular questions or concerns about stress and cracking of brick and mortar at your home? We can help.
If you need help to understand what is happening with your brick, or what makes the best sense for you, or maybe just need reassurance where you stand with brick maintenance investment in the future; feel free to call on our team of masonry experts. And we are always ready to answer questions or provide a free estimate.
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