Cracks need to be treated only when they are a potential threat to the durability of the reinforcement or are causing unacceptable leaks. Injection should not be used for cracks that are the result of corrosion of reinforcement. There is a lower limit of about 0.1 mm on the width of crack that can be successfully injected, depending on the injection resin. Polymers used in injection of cracks include epoxies, acrylics, polyesters and polyurethanes. Each has different properties and is used for different circumstances.
The surface of the concrete is first cleaned alongside the crack to remove loose friable material and contaminants. The crack itself is blown off with clean dry air so that resin can flow freely into and along the cracks. Resin is then injected under pressure either into inlet ports that have been stuck to the concrete surface over the crack or through holes drilled to intersect the crack. Resin injection is a skilled process and should only be undertaken by specialists.
Injection is undertaken using a pump to apply pressure. On larger jobs the pump may incorporate measuring and mixing equipment to deliver the resin thoroughly mixed together in the correct proportions of its components. On small jobs, injection may be undertaken using a hand pressure gun. A variation to this process uses vacuum rather than positive pressure. This is said to give better control over the injection process.