While you want your polished concrete to look attractive and smooth for as long as possible, accidents happen, especially in high-traffic areas or commercial work spaces. When working with muriatic acid or other acidic materials, spills can damage your polished concrete, creating unsightly, unattractive spots. Fortunately, just like we can repair and remove scratches and gouges, we can also remove acid stains from polished concrete.

Check out the video below or read on to learn the steps to restore the damaged area to a like-new appearance and blend in with the concrete around it.

Why Does Acid Stain Polished Concrete?

When acids, such as muriatic acid, battery acid, or even acidic materials like red wine or vinegar, hit polished concrete, it creates a chemical reaction. In fact, because concrete has a high pH, acids are often used to clean concrete slurry and remove where wet concrete has splashed on surfaces and dried.

With polished concrete, the acid reacts and erodes the cement from the sand particles. The stains revert the concrete back to a white-gray color and are etched and rough, standing out against the smooth, darker, finished concrete.

Repairing Acid Stains on Concrete

Grinding and Smoothing the Damaged Area

Because the concrete was reverted back to its more natural state, we basically begin the polishing process from the beginning. First we use a 100-grit diamond pad to cut through the existing polish and damage in the area, and flatten the area, though it’s important to not extend past the damaged area. Otherwise, that is more work that goes into blending and polishing during the next steps.


Once the concrete has been etched, we want to make it harder and more resistant to damage in the future. To do this, we add a concrete densifier that reacts with the concrete, creating more crystalization, filling in gaps, and increasing the surface area.

The densifier is applied and rubbed in to the concrete, then the excess is wiped away.

Finer Grinding

Once the densifier is applied, we tape off the area to keep a visual cue of where we’re working so we don’t grind through the non-damaged area and making our work harder! Then, we take a 200/400 grit to do a finer grind.

Make sure you look for an even color to make sure the area you’re repairing is all the same – a whiter shade on the outside of the repaired section means the repair won’t blend in with the current polished concrete.

After that, we move to an 800-grit diamond for the fine grinding, and we extend outside our visual circle (removing the tape of course) in order to prevent a harsh line of repaired polished concrete to existing concrete.

Burnishing and Blending the Stain

Using a 3500-grit diamond will create a section that is too highly shined in comparison to the existing space, so we use a burnisher or swing machine to polish and get it to match as closely as possible.

It will most likely look lighter than the floor around it, solely because the concrete has been opened and newly polished. Over time, it should darken to match the existing slab.

Contact Us for Concrete Grinding Supplies

We carry everything you need to repair concrete, including chemical densifiers, floor grinders, and floor grinding accessories, including diamond pads. To learn more about our products and get the best possible price, speak with a product expert today by calling  815-472-9754.