Why Is My Concrete Stained?

If you have bare concrete in your basement or garage, or even outside, and you have started to notice stains appearing from seemingly nowhere, it is normal to be concerned. After all, these stains are unsightly and can be symptoms of unseen damage in your home. Broadly speaking, there are two main causes of concrete staining: 

Defects in the Mix 

If concrete is to perform to its full potential, it must be mixed properly and to the right proportions. If the mix is measured or applied in a wildly inappropriate manner it can quickly break down and crumble. This is highly uncommon, however, as there are many safety checks in place in the construction process these days. A minor imbalance, however, can cause concrete to deteriorate in a superficial or cosmetic way over time. 

Staining, pitting, flaking, crazing, and bubbling are good examples of this kind of cosmetic damage. These issues can be caused by an improper water-to-cement ratio at the surface levels, inadequate or inappropriate curing, and cement alkalis, among other things. In many cases, purely cosmetic staining can be removed with a power washer or chemical cleaning mix, but it is likely to reoccur over time. 

Environmental Factors 

If the concrete in your home was properly mixed, laid, and cured but is still starting to stain, it is likely a result of damage or adverse environmental conditions. In these cases, the staining is likely to remain localized to one area, or certain areas. Meanwhile, staining as a result of defects tends to span the whole surface in varying levels of severity. 

The environmental factors that are most likely to cause concrete damage are dampness and pressure. If your basement is incredibly damp, for example, you are more likely to see surface-level staining, pitting, and bubbling in the concrete. However, if pressure is the cause of the damage—for example, pressure from foundation subsidence—you are far more likely to see cracks forming. Of course, this can cause dampness and stains too.