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How to Properly Repair Concrete

Concrete is a great material for many different types of structures but it will show wear-and-tear over time. It’s important to repair any damage as soon as possible to prevent further deterioration.

Concrete

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Concrete repair can be structural or decorative, but the best results come from thorough preparation of both the surface and the concrete itself. The right mix, application, and curing of the repair product is also important. Structural repair focuses on strengthening the existing concrete and preventing future damage. Decorative repair is usually for aesthetic enhancements such as staining or painting.

The first step in any concrete repair project is to prepare the surface for the application of a new coating or topping. This includes thorough cleaning to remove dust, dirt, debris, oil, and other contaminants. It also includes repairing any cracks and holes in the concrete. It is also a good idea to grind the concrete to give it an open surface profile and to make sure there are no areas where the concrete is soft or loose.

A good contractor will have experience with a variety of concrete repair methods and materials. This helps them diagnose current problems and anticipate potential problems that may occur during the repair process. They will know how to properly use the equipment and tools needed for the job and will be able to recommend the best method for each particular situation.

During the concrete placement process, interior concrete surfaces are typically hard-trowelled and exterior concrete is lightly broomed to impart a nonslip surface. This surface profile may interfere with the bond of certain topical repair materials. The contractor should evaluate the surface to determine if it is ready for repair.

If the concrete is spongy, sagged, or has soft spots, it will need to be reinforced before any repairs can be made. This is especially true if the cracks in the concrete are forming near the surface. The contractor should determine the type of cracking that is occurring and the extent of the soft or sagged area.

Some contractors choose to use a liquid bonding agent as part of the concrete repair process. This is generally applied with a brush or rag, although it can be sprayed if needed. The bonding agent is designed to help ensure that the new topcoat will adhere to the concrete. The contractor should make sure the bonding agent is saturated with water to prevent off-gassing.

Materials

Concrete repair materials can range from basic vinyl patching compound to high-performance epoxy resins and hydraulic cements. They must be compatible with the existing concrete and designed to perform under the required load conditions of the repair. Preparing the old concrete surface for the application of the repair material is critical to its durability. It is important to clean the area to be repaired and remove all loose debris. This step is often ignored by contractors and can result in premature failure of the repair.

Once the preparation of the concrete has been completed, it is time to choose the best material for the job. It is a good idea to talk with a concrete supply professional about the repairs that are necessary and what type of repair material would work best. Different types of repair materials are available for various installation techniques and different repairs. Repair materials are classified based on their fresh state properties, such as pumpability, slump, flow and hang/stickiness. They can also be adapted to different placement methods, such as form-and-pour repairs, hand or machine-applied aggregate, tremie concrete repairs and dry-sprayed shotcrete.

The fresh state properties of a repair material can be modified to improve their performance by using admixtures, mineral and polymeric additives, waste materials and nanomaterials. The addition of these constituents can also give repair mortars and concretes signature properties, such as self-consolidating capabilities, low permeability and autogenous, self-healing characteristics [6].

Some repair methods use precast or pre-cast products, such as prestressed steel cables or rods that add compressive forces to cracks, making them more stable than standard concrete. Others include injecting epoxy into the cracks or applying a concrete patch. A drilling and plugging method also is used to make small vertical crack repairs.

A simple patching mix is available from many manufacturers, such as Sakrete(r) concrete crack filler (BOM #120026) or Tenon(r) partial depth concrete patching mix (BOM #100472). These mixes contain a combination of Portland cement and oven dried aggregate that can be mixed with water to create a patching mixture. They are ideal for repairing and patching concrete surfaces, leveling concrete floors, adhering pavers to concrete steps or sidewalks, repairing concrete pavements and industrial flooring and restoring cores in structural concrete.

Application

Concrete repairs must be done correctly to help ensure that they last. It is important to follow the steps of preparation, application, curing, and maintenance for the best results. These steps will depend on the size of the repair and type of concrete being repaired. For large concrete projects, a professional engineer experienced in concrete construction should be consulted.

The first step in any concrete repair is to clean the damaged surface. This can be achieved by a variety of methods, including physical or mechanical techniques like power washing, shotblasting, and grinding. The concrete must be free of dust, debris, oil, and existing paint to allow the repair materials to bond well with the substrate.

Once the concrete surface has been cleaned, it is vital to profile it. This process involves scraping the concrete to remove the deteriorated material. This should be done with a light touch, as the integrity of the sound concrete beneath should not be compromised. A concrete profiler can be used to achieve the proper profile for the repair.

Next, the concrete must be saturated. This will be done by spraying the concrete with water to fill the pores. This will prepare the concrete to accept a new repair, and will also help prevent the repair material from prematurely drying out.

After the concrete has been saturated, a primer or bonding agent can be applied. Products like SpecChem’s Strong Bond and SpecWeld serve as the glue that helps cement repair materials adhere to the concrete surface. These products should be applied while still tacky to ensure that they bond well with the concrete.

If the concrete is being patched to repair cracks, it is important to use a concrete patch that can withstand shear and tensile stresses. This will help to reduce deflection and make the structure safer under service loads.

Keeping your concrete in good condition is a great way to reduce the cost of future repairs and extend its lifespan. However, it is important to remember that even with the most thorough preparation and application of concrete repair materials, there will come a time when full replacement may be necessary. If the cracks are deep and extensive, or if the concrete is sinking more than 8”, it might be worth considering replacing the entire slab of concrete instead of trying to repair it.

Curing

Curing is a critical stage in the development of concrete strength. It involves maintaining the desired temperature and moisture conditions, both at depth and near the surface, for extended periods of time. Concrete that is properly cured achieves sufficient strength to resist shrinkage cracking, abrasion and scaling. It also has an adequate density to withstand traffic and other loads. Concrete that is not cured adequately or at all develops weaker strengths and may have other unfavorable characteristics such as excessive cracking or low durability.

There are many ways to cure concrete. The method that is best for your repair depends on the size and location of the damaged area, the type of repair, and its environmental exposure. In all cases, it is important to give the concrete enough time to set.

If the concrete is exposed to too much sunlight or other heat it can dry out too quickly, which decreases the strength and durability of the repaired section. It is also important to seal the concrete to prevent water vapor and other contaminants from penetrating the concrete and causing further damage.

It is also possible to use curing compounds or other materials to help keep the concrete damp. These materials can be applied to the surface or placed inside a plastic sheet or blanket that is hung over the concrete. This method is particularly useful for structures that are exposed to a large surface area in relation to the depth, such as road slabs or canal linings.

There are other methods of repairing deteriorated concrete, such as epoxy injections or carbon fiber wraps. These methods can be used for shallower repairs that cannot be done with a scratch coat, but they still require the concrete to be dry and free of contamination prior to application. These techniques can also be effective in repairing seismic or other structural damage to existing concrete. In these cases, it is advisable to perform a visual examination, delamination survey and potential mapping of the structure before the repairs are initiated. This will help to identify the extent of the deterioration and determine the appropriate repairs.