What Does Acid Wash Do to Concrete?

Concrete is used for many different purposes, from garage floors to restaurant patios to commercial buildings and offices. In addition to being visually attractive, it’s also durable and long-lasting. However, before you can use a concrete stain or epoxy coating on your home or business, you must first prepare the surface properly.

Acid Washing & Etching

There are several methods for preparing concrete to receive an epoxy finish, but acid washing and etching are the two most common. The first method, called acid washing, is a process that removes stains and other surface contaminants from concrete surfaces by using an acidic solution.

The other method is called etching, which is a process that erodes the surface of concrete in order to expose its pores and offer a clean slate for a new coating. It’s not a replacement for grinding a surface before epoxying, but it is a viable option when grinders are not available or the concrete is too tightly troweled to safely remove dirt with a regular power washer.

What Does Acid Wash Do?

A common acid cleaning solution, muriatic acid, is diluted with water in a sprinkling can and then applied to the concrete. It can be applied to concrete in a variety of ways, including by hand or with a power washer.

It is best to apply acid wash in small sections to avoid splashing onto adjacent surfaces. The sprinkling can should be held close to the surface and used with a push broom or long masonry brush, distributing the acid evenly.

After the acid has been applied, rinse the concrete with plenty of water to ensure all the residual chemical is removed from the surface. This will prevent any lingering stain from saturating the concrete and ruining the finish.

The acid wash will eat into the concrete, so it’s important to keep the surface well-dampened throughout the process. This will help the acid not to eat away at the concrete’s structure, which can cause scaling, pitting, and peeling.

Wetting the Concrete

Before you can begin applying the acid stain to your concrete, you must first dampen it so that it absorbs more uniformly. The easiest way to do this is by spraying a light mist from your hose nozzle. If your concrete is particularly porous, you may need to dampen it more thoroughly.

If you’re not sure how to dampen the concrete, consult the manufacturer of your acid stain. Be sure to check the label’s instructions on how much water to use with the acid stain, as different manufacturers recommend different amounts of water for their products.

Step 2: Prep the Concrete

The surface of poured slab concrete should be smooth, but large protrusions and rough patches are not recommended. To get a smooth surface, you can use a grinder (available for rent at construction rental centers) fitted with an abrasive silicon carbide disk to remove hardened tar and paint.

Then, you can stain the concrete as desired. You can choose from a wide range of colors, but be sure to read the directions on your concrete stain and be aware of any existing color that might affect its final appearance. It’s also important to be careful not to stain any areas that are bare or damaged.