Dynamic Cracks versus Static Cracks – What’s The Difference?

Written by Steve Maxwell of BaileyLineRoad.com

While it’s obvious that cracks in concrete can be a problem because they can let water and harmful soil gases into foundations, they can also be a sign of failing structural integrity of other concrete structures, too.  All this is why you need to answer one big question before you set out to repair any kind of concrete crack.  Is the crack dynamic and continually getting worse, or is it static, stable and more or less unchanging over time?  This is a fundamental issue and figuring out what’s happening is the first step to fixing any concrete crack properly. You need to determine the status of the crack because this affects how repairs happen.

Dynamic means “changing” and dynamic cracks in concrete are always the most serious because they’re probably getting bigger and possibly heading towards some kind of structural failure.  Whether a particular dynamic crack ever progresses that far can’t be known ahead of time, but that’s where they’re headed.  Structures are sometimes constructed on unstable ground and this is the leading cause of dynamic crack formation.  The good news is that most concrete cracks are static – not moving – and not enlarging, though this doesn’t necessarily mean they don’t expand and contract seasonally.  While static cracks may not be getting larger over time, that’s not to say that they don’t get wider and narrower seasonally from summer to winter, needing stabilization if you want to maintain an effective seal against water and radon gas.

Observations over six months or more is the only way to determine for sure if a small crack is static or dynamic, and this is especially worth doing if the crack is horizontal.  You’ll find that non-structural static cracks are usually vertical or diagonal in orientation, and typically never get bigger than ¼-inch wide.  And while it’s true that dynamic cracks all begin as narrow hairline fractures, one sign they’ll probably get wider over time is a horizontal orientation.  Dynamic cracks are one sign of a failing foundation and this almost always shows up as horizontal cracks.

Monitoring Cracks

If your client allows you the time, observation is the best way to begin a foundation repair that you suspect involves dynamic cracks.  Try your best to get permission for this to happen.  Use a Sharpie marker and a ruler to draw straight lines across the crack at 4-inch intervals, as close as possible to 90-degrees to the crack.  Carefully measure the width of the crack at each marker line down to 1/32-inch, then mark this dimension and the date on the wall next to the line it applies to.  Check back every few months, then measure and record details again right on the wall before comparing them.  If the crack is getting larger over time, then the issue is dynamic and structural.  You’ll definitely need to design a repair strategy that includes both strength and sealing capabilities.

The dirty little secret of the concrete crack injection industry is that injection alone of dynamic cracks is a risky fix that’s likely to fail in the future.  This is especially true because injection alone has little to no ability to stop new crack expansion.  Legitimate repair of dynamic cracks always involves some kind of structural reinforcement as well as sealing, and carbon fiber systems offer the best strength of all options.  When it comes to static cracks, injection alone offers a better chance for a permanent repair, and this is the industry standard.  That said, injection alone is still no guarantee, even with static cracks. The reason is because static cracks aren’t always entirely static.  They can expand and contract seasonally, as you’ll see.

Don’t Trust Static Cracks

While it’s true that an actual dynamic crack is definitely getting bigger over time, that doesn’t mean that a static crack doesn’t change over the course of a year without necessarily growing larger over those years.  Changes in temperature can cause an otherwise static crack to open and close enough seasonally to break the seal of an injection-only repair.  Even a narrow new crack appearing alongside the seal can be enough to let in water and radon.  This is the argument for using carbon fiber reinforcement over both dynamic and static cracks after injection has been used and it makes sense.  Not only will the carbon fiber encasement stabilize and halt any seasonal expansion and contraction of crack width, but it also creates a waterproof/gas-proof seal on the face of the wall.

Rhino Carbon Fiber concrete repair systems uses woven carbon fiber fabric and epoxy resin to halt the movement of dynamic cracks and to cover and seal static cracks.  When applied correctly to clean and prepped concrete, the resulting repair is stronger than the underlying concrete.  The key to an optimum repair is the use of the right kind of carbon fiber fabric.  This is another reason it makes sense to monitor concrete cracks before you attempt a repair, if you can.  It’s useful to know which way the sides of the crack are moving.

Dynamic cracks are always more of a concern than static cracks, but both should be taken seriously. Always educate your clients about the nature of their concrete cracks and why you recommend certain repair strategies before you begin work.  Education is essential for getting client buy-in when it comes to designing a proper repair approach, especially when that repair involves more than just basic steps. If in doubt, err on the side of both sealing and carbon fiber reinforcement and you’ll be building a reputation for reliable concrete repair that crack filling alone can’t deliver.

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About the Author

Steve Maxwell is founder and publisher of BaileyLineRoad.com with 30 years experience explaining building technology for professional audiences. Visit rhinocarbonfiber.com for more information about carbon fiber structural repair systems.