Written by Angie List and published on https://www.angieslist.com/.
Before you can repair anything you have to know what caused the problem in the first place and you have to understand how it is supposed to work. Only then can you make an intelligent decision on how to do the repair.
With any concrete repair, take that lesson to heart and you’re off to a great start. First figure out what caused the damage, do the necessary preparation of removing any unsound concrete and contamination, then install a repair designed to solve the problem. The worst thing you can do is make a repair that doesn’t last. Someone once told me that over 50% of concrete repairs fail again within two years. That is not a track record that inspires confidence.
What You Need to Know about Concrete Repair
Before hiring a contractor to replace concrete in and around your home, one highly rated provider explains how to diagnose when replacement is actually needed.
On this ever shifting piece of the earth’s crust we all live on, there are two unequivocal facts about our concrete: it is gray and it cracks. The information below will specifically address crack repair on surfaces where an overlay will be installed. Overlays considered include, but are not limited to: polymer modified concrete overlays, tile, stone, epoxy and other hard surface products that will be bonded to the repaired surface.
When most of us see a crack in our concrete, we immediately assume that the concrete is damaged beyond repair or that we have some type of structural problem that can only be fixed by removal and replacement. It is this uninformed thought process of the consumer that keeps many concrete removal and replacement companies in business.
How to Prevent Concrete Cracks
Over time, your concrete is susceptible to cracking. Here’s what you can do to prevent it and protect the look of your sidewalk or driveway.
What causes concrete cracks
Cracks in concrete can be the result of a multitude of conditions related directly or indirectly to the soil substrate or existing site conditions, mix design, over hydration of the surface during placement, improper steel placement or reinforcement, insufficient grade preparation and inadequate joint design. Other more complicated and complex causes for cracking in concrete are possible, and in most cases can be diagnosed by a knowledgeable concrete professional.
Before we get into the meat of the discussion, let us first discuss the fact that the homogenous prescription to repair a crack should not overshadow the underlying cause of the crack. Therefore, the cause should be considered and when possible, addressed prior to prescribing the appropriate repair method.
Different types of concrete cracking
There are several different types of cracks in concrete. This is important because each type of crack requires a different repair. Below are listed the types of cracks and the appropriate repair for each.
The first type of crack is a “check crack” or shrinkage crack. Shrinkage cracks are easily identified and recognizable as they usually appear to be discontinuous and are typically in the surface of the concrete only. Most shrinkage cracks are approximately one sixteenth of an inch wide and are not typically considered to be a defect in the concrete, as all concrete shrinks a bit during the initial hydration period.
Repairing of this type of crack prior to the installation of an overlay is typically not required, although I do recommend an anti-fracture membrane be installed as a safety precaution to protect the overlay from potential reflective transfer through the overlay.
The second type of crack in concrete is called a “structural crack.” Structural cracks are also known as settlement cracks, shift cracks and load cracks depending on the area of the country. The cause of settlement cracks can vary but are typically related to pour grade preparation or shifting soil.
Structural cracks are typically continuous and travel from one side of the concrete to the other. It is very important to note that though the result is not guaranteed, this type of crack typically requires injection of a structural epoxy.
The layperson is often mislead into believing that this process is intended to bond the concrete back together. Though it would seem that the injection of the epoxy bonds the concrete back together, this is not the primary initiative. The epoxy (when hardened) acts as a liquid shim which binds or prevents the inward movement of the crack, effectively preventing the crack to close due to any additional movement. After the crack has been injected, an anti-fracture membrane should be installed over the repair area to prevent reflective energy transfer.
The third type of crack, which is the least responsive to the aforementioned repair method, is the “off-set structural crack.” An off-set structural crack is when the crack exhibits a raised area on either side of the crack itself.
Also referred to as a twisted crack, the off-set crack does not move only in and out, but also moves up and down. In this case, shimming of the crack will not work due to the up and down movement and shear load caused by the movement, thereby rendering the use of an anti-fracture membrane useless. Instead, local removal and replacement of the affected area is the only effective repair method recommended.
Before you make the decision to endure the extortionate costs and seemingly inestimable downtime of removal and replacement, you should have the defective areas evaluated by a competent concrete professional who knows the facts on how to address cracks and how to evaluate the concrete’s condition.
Original post here https://www.angieslist.com/articles/what-you-need-know-about-concrete-repair.htm.