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How to Fix a Bad Concrete Stain Job

In modern construction, concrete pads often incorporate added features like stamping and staining to imitate natural materials. The process involves adding colorants to either new or old concrete to change the color.

This may be done to match an exterior color scheme or to replicate the look of natural stone, like slate. This project often requires a fairly high level of skill and experience, because the inconsistent application can result in an unprofessional-looking job that will likely need to be corrected.

Today, we will discuss a few options commonly used to correct a bad concrete staining job, and how to go about it.

Can I Fix a Bad Concrete Staining Job Myself?

If you are an experienced do-it-yourselfer, you probably have the skill and tools needed to make the repair, however, it really depends on the severity of the problem. Correcting a poorly done concrete staining project is not particularly complex, but the job usually requires the use of abrasive tools and harsh chemicals.

Concrete is a very tough material, so working with it requires an aggressive approach. Therefore, only those DIYers with the appropriate experience and safety gear should attempt the project. 

In most situations, the repair will involve the use of a pressure washer, caustic chemicals (like acid), and/or abrasive machineries like sanders and grinders. Using any of these methods requires a thorough understanding of the process and the use of appropriate safety gear to do the project safely.

These include eye and skin protection, respirator, good ventilation, and any other appropriate equipment to prevent injury. In some situations, all three techniques may be required to make the repair, so here we will describe each method and offer some insight to how a professional might approach the project.

What Is the Best Method For Fixing a Bad Concrete Stain Job?

The answer will often depend on the severity of the project. Some stains are relatively easy to remove, while others are not. The condition of the problem will often dictate if the stain will require mechanical abrasion or a simple cleaning. In modern construction, concrete is typically sealed using a concrete sealer, which prevents dirt, grime, and other contaminants from contacting the surface of the concrete and accumulating. This makes cleaning and maintaining concrete much easier, however, the same process can encapsulate a bad staining job, so if this occurs the sealer must also be removed to correct the color. 

There are several ways to remove a poorly done concrete staining job. These include chemically dissolving the stain, physically removing it, or in many situations, both techniques will be used. Here we will discuss a few concrete stain removal options and why the pros may use one over the other:

Cover the Stain With Concrete Paint

Undoubtedly, the easiest and most common way to solve a botched concrete staining job is to just cover it up. This option will involve preparing the surface to accept a new finish and then applying it. In most cases, concrete stains are petroleum-based, so it is not acceptable to use latex-based paint or stain unless the old finish has been neutralized.

This typically just involves using a primer to prevent any chemical reaction between the old stain and the new paint. In these situations, once the old stain has been primed and sealed, the new finish can be applied by spraying, rolling, or brushing.

Pressure Washing

If the project will require the removal of the stain, professionals will usually use the least invasive method first, which in many cases is pressure washing. Pressure washing involves the use of a machine called a pressure washer.

These machines are often gas-powered to deliver very high water pressures. This concentrated pressure is then used to abrade the concrete as required to remove the stain. Different spray tips are used, depending on how well the stain has bonded to the concrete.

Some tougher areas may require more pressure than others to remove the stain, so pressure washers come equipped with a pressure regulator. This allows the user to adjust the pressure as needed to remove the stain without damaging the concrete.

In some situations, the stain is very hardened and has penetrated deep into the surface. In these instances, often a detergent is added in addition to pressure washing. Most pressure washers include a reservoir for soaps and other detergents that are added to the water as it exits the wand. This method is especially effective on concrete stains because the detergent helps to break down the oils in the stain.

Detergents can be added as needed as long as they are effective, but after the stain is removed, the area should be completely rinsed to remove any soap residue. New stains or paint may struggle to bond with the concrete if any residue remains because the residue will also begin to break down the new finish.

Using Chemicals

Often, if pressure washing doesn’t do the trick, the next step is to use some sort of chemical solvent to break the bond between the stain and the surface. This can be done using petroleum-based solvents like acetone and turpentine, or acidic solutions like muriatic acid to break down the stain.

Most professionals will then use a coarse brush to loosen the stain and lift it. However, care should be taken when using these chemicals, as most of them are caustic and may cause personal injury. As with a detergent solution, the surface must then be thoroughly rinsed and allowed to completely dry before applying a new finish.

Mechanical Abrasion

In some severe cases of staining, pressure washing, detergents, nor chemicals are effective in removing the entire stain. In these situations, professionals will often use a floor sander or grinder to scuff up the surface of the concrete. This is often done with machinery designed for sanding hardwood floors, like barrel sanders and rotary sanders.

These machines are essentially just large versions of common tools like belt sanders and disc sanders we may already be familiar with. Because concrete is much denser and harder than wood, the process typically requires more aggressive sanding to remove the top surface.

This is done by using very coarse sanding pads to abrade the surface and literally remove a layer of concrete. This method works very effectively and is sometimes the last resort when other methods have failed. However, this method is messier than others, because it creates dust that can become airborne. Therefore, all the appropriate safety gear should be used, including a respirator.

What Are My Options After the Stain Has Been Removed?

Pressure Washing

Once the stain has been satisfactorily removed, the surface can be inspected. If the surface was receptive to pressure washing, often the next step is to let it dry thoroughly. After the surface is completely dry, it should accept a finish. 

Rinse the Chemicals

If the surface requires a more aggressive approach using chemicals, the surface will still need to be lightly pressure washed to ensure that any residue from the chemicals is removed.

The pros will often use the detergent feature found on most pressure washers and lightly soap and rinse the pad, and then allow the concrete to dry completely. If the surface is still damp when the new finish is applied, the water can displace the new stain and prevent it from soaking in. 

Mechanical Sanding

When all else fails and mechanical sanding is required, the top layer of concrete is removed. In this situation, often the pad will simply be swept and vacuumed to remove any residual dust instead of pressure washing the pad. For a very smooth finish, the pros will dampen a sponge and lightly wipe away any additional dust or other contaminants.

However, it is important not to mop the concrete, as this will likely add too much water to the surface. This excess water will be absorbed into the concrete and will require additional drying time before any new finishes can be applied.

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