How to Treat Discoloured Concrete Surface

Concrete discoloration is simply the change of the designated color of concrete. This could be due to the presence of calcium chloride in concrete, cement and additives, improper curing, environmental conditions, and faulty finishing works.

Discoloration can be minimized by reducing the effect of the factors mentioned above.?However, if a contractor encounters dark spots, strips, and blotchy concrete, certain remedies can be undertaken to lessen the effects.

The treatment technique can be selected based on the cause of discoloration, and it should be applied when the concrete is fully cured.

How to Treat Discolored Concrete Surface?

Several remedies are available to mitigate?concrete surface?discoloration. The right strategy is to begin with the easiest and simplest technique:

1. Cleansing

For mild discoloration, flush the hardened surface with hot water and scrub with a stiff brush to even out some of the variability in the concrete’s moisture and mineral build-up. It may be necessary to carry out this process until the discoloration disappears.

After the concrete dries and discoloration disappears, it should be sealed with a new, light coat of concrete sealer to protect the work that has been done.

2. Use of Acid Solution

If discoloration is severe, use mild acid solution, for instance, 1% to 3% muriatic acid. The right amount of acid should be used as a high concentration of muriatic acid creates blemishes and weakens the concrete.

The depth of acid ingression into concrete can be controlled by flooding the concrete surface, letting it dry, and then applying the acid solution. The longer the concrete stays dry, the deeper the acid solution can penetrate. Therefore, it is advisable work on a manageable concrete surface and control acid penetration based on the drying time after flooding.

After applying the acid solution, wash the area thoroughly with clean water within 15 minutes.

3. Tinted Color Sealer

A tinted color sealer is another option to hide discoloration if concrete washing fails to remove discoloration and the use of an acid solution is undesirable. Unlike acid solution and acrylic sealer, a sealer will not change the look of concrete if it penetrates the surface.

The acid creates a marble-like finish, whereas acrylic sealer darkens the surface and leaves behind a low-to-high gloss finish. If using an acrylic sealer, apply a solvent-based acrylic and initially apply the product to a test area to check whether it provides a consistent finish. It is possible to add color to acrylic sealer to completely conceal the discoloration on the concrete surface.

4. Special Coating

A thin polymer-modified coating can be used to cover the discoloration and stain. This type of coating is commonly utilized to cover graffiti.

5. Diammonium Citrate

Another method to remove discoloration is the application of diammonium citrate which is used for severe discoloration. Diammonium citrate is a salt compound utilized for a buff.?

The substance is prepared with water and left on a concrete surface for around 15 minutes, then brushed thoroughly and rinsed.?This material is expensive, so it should be considered only after trying the other less costly methods.

6. Concrete Resurfacing

If the discoloration and stain issue is severe and cannot be fixed properly, applying a concrete overlay over the entire area to cover the distorted color can solve the problem.

Some of the treatment methods used to treat discolored concrete are:

1. Cleansing

2. Acid Solution

3. Tinted Color Sealer

4. Specialty Coating

5. Diammonium Citrate

6. Concrete Resurfacing

Causes of Concrete Discoloration

Concrete discoloration is a change of designated color due to calcium chloride in concrete, cement and additives, improper curing, environmental conditions, and faulty finishing works.

The drawbacks of a high concentration acid solution on concrete

A high concentration of muriatic acid creates blemishes and weakens the concrete.

When concrete resurfacing should be selected for discoloration treatment

If the discoloration and stain issue is severe and cannot be fixed properly, applying a concrete overlay over the entire area to cover the distorted color is a suitable solution.

How to control the penetration of the acid solution into concrete during discoloration treatment

The depth of acid ingression into concrete can be controlled by flooding the concrete surface, letting it dry, and then applying the acid solution. The longer the concrete is dry, the deeper the acid solution can penetrate. Therefore, it is advisable to work on a manageable concrete surface and control acid penetration based on the drying time after flooding.

Credit: The Constructor