Rust makes noticeable and ugly stains on concrete surfaces, annoying homeowners to no end. Most people respond by dumping gallons of bleach on the unsightly stains, hoping to clean them away. But can bleach remove rust stains from concrete?
Bleach will not remove rust from concrete because it doesn’t penetrate below the surface. Since concrete is highly porous, rust stains penetrate deep below the surface. Bleach reacts with the rust stain on the surface, turning them colorless, exposing the rust stains in the layers below.
A quick look into how bleach works can explain why it’s ineffective in removing rust stains from concrete.
How Does Bleach Work?
Household bleach comprises water, a small salt content, and sodium hypochlorite – the main active ingredient. Sodium hypochlorite is liquid chlorine, and bleach contains 5 to 6% chlorine.
Some insights into how color works is necessary to understand how bleach removes stains or turns colors white.
Light comprises particles called photons that travel in waves. Light waves fall into three categories, grouped by their wavelengths, and some are not visible to the human eye.
The infrared light and ultraviolet wavelengths are invisible to the naked eye. The human eyes perceive wavelengths between 400 and 700 nanometers as colors. For instance, you’ll see a wavelength that’s 475 nanometers as blue and one that’s 650 nanometers as red.
Like most other substances, rust comprises molecules held together by chemical bonds. Some of these molecules are called chromophores and give the rust stain its characteristic reddish-brown color.
Since rust is a compound of iron, it comprises a complex network of double bonds between carbon atoms and the chromophores. These chemical bonds make the rust stains visible to the human eye.
Chlorine bleach releases oxygen molecules through oxidation and breaks up the chemical bonds in the chromophores.
Damaging a chromophore’s structure interferes with its ability to reflect colors. It either stops reflecting color or reflects colors beyond the visible spectrum.
The human eye perceives the absence of color as white.
Why Bleach Does Not Remove Rust Stain From Concrete
When you apply household bleach on a rust-stained concrete patch, it only reacts with rust stain on the surface. It breaks up the color pigments on the surface layers, turning them colorless.
However, since concrete is a highly porous material, rust stains penetrate deep into the surface.
Chlorine beach proves ineffective in removing rust stains from concrete because it only breaks down the stains on the surface. The stains etched deep into the concrete surface remain untouched and visible through the whitened upper layers.
Household bleach doesn’t remove rust stains from concrete because it doesn’t penetrate below the surface. Rust stains tend to be deep-seated because concrete is a highly porous material.
Acids break down and dissolve the rust, while water-based rust removers lift the rust away from the concrete surface.
Strong acids such as phosphoric, hydrochloric, and sulfuric acids remove rust but are highly corrosive in high concentrations.
Weaker acids such as oxalic, citric, and muriatic acid are less caustic and won’t discolor a concrete surface.