The Inevitable Situation: Repairing Cracks Under Resinous Coatings
by Paul Scheidmantel - Sales Director
Although there are few guarantees in life, one guarantee a contractor can always count on is concrete cracks. Despite the quality of the materials and workmanship, cracks happen. The bigger question is how to fix them, especially when that concrete is hidden under a beautiful resinous coating.
Existing cracks and joints in concrete substrates can pose a difficult challenge for aesthetics and functional aspects of seamless coating systems. It all begins with understanding the type of crack or joint. This can help minimize the impact of future movement, as well as determine the appropriate course of action to best alleviate the stress on the crack or joint. As a professional, it’s also very important to understand the customer or end user’s expectations, determine whether their budget meets the method of the recommended repair and fully communicate the worst case potential remediation cost upfront. This will hopefully avoid confusion and manage their expectations since moving and dimensionally unstable substrates are likely to crack again.
Crack and joint remediation can become costly, and in some cases are cost prohibitive to the end user. Accepting the reality that Mother Nature usually wins the crack battle when movement continues means that ultimately some cracks just are not worth paying for twice.
Joints have a purpose and should be honored to the surface. With that in mind, some regulations or desired aesthetic sway the customer to choose a method of construction that delivers the look they want, which isn’t always the best method of construction.
Typically, joints do not behave well under seamless coatings, but can be bridged if properly treated, as with dimensionally stable cracks. Before joints or cracks can be covered or bridged, the contractor must determine what kind of joint is present. There are three distinct types:
- Control – Joint placed to reduce shrinkage stress, as well as provide a weakened point to ideally force the crack to break where desired.
- Construction – Joint placed between two separate pours or batches of concrete, which is called a stop point or “cold joint.” This joint may incorporate a metal strip that protrudes to the bottom of the slab, contain metal dowels between separate concrete pours or a formed and/or pre-molded edge.
- Expansion – Joint placed to promote or allow movement between separate slabs of concrete. Expansion joints are also used to absorb vibration, expansion/contraction movement of the concrete, reduce/isolate movement from ground settlement or earthquakes, and more.
How Cracks Happen
Cracks are caused by either stress from shrinkage or force, such as overloading weight, shrinkage or some form of movement. Regardless of how they occur, cracks were not necessarily intended to appear where they present themselves, which is why contractors tend to create “control joints.”
The Repair Process
When tackling the problem of a crack, it’s a best practice to treat them as if they are still moving and are NOT dormant. Improper crack repair will only cost the customer more in terms of time and money, as the crack will likely reappear. Contractors should always cut out the broken or loose concrete, dirt and debris to ensure proper bond of the repair material.
It is difficult to ensure a crack repair material is fully filled, from top to bottom of the crack or joint. In situations that the void is wide enough for liquid to pass through, contractors may need to use foam backer rod to seal off the void or use sand in irregular cracks. In the latter case, it’s recommended to fill the void until the sand stops sinking, then use a broom to remove the top ½-inch of sand from the crack prior to filling with the desired patching material. This will help reduce waste of the patching material, while also reducing the likelihood of needing to make further repairs for holes that may reappear due to sinkholes within the crack (as shown in the image below).
Once the repairs have cured, the cracks and joint can be ground flush to the surface.
With joints that have been repaired, and the sides need to be narrowed at the width, the contractor should recut the repair material to create a new joint at the desired width, then fill with an appropriate joint filler. Done properly, the outcome looks clean and can last for a long time without significant future cracking. The fill should remain in the crack or joint as the material was properly anchored to the sides of clean concrete.
For any questions or advice on tackling a particularly challenging crack, there are professionals ready to work through any problem situations. Please contact our Technical Department for advice.