Three Most Common Concrete Stains

Although concrete is a fairly low maintenance product, it can still have issues with staining.  Understanding how different materials can affect your concrete can help…

1. Rusting Pop-outs


Have you ever seen rust spots on a driveway where it looks like some type of metal is sticking though the concrete causing it to rust?  Although this could be possible, the usual cause of rust spots on driveways are due to iron stone or coal within the concrete. 

Concrete suppliers are allowed a certain amount of this type of stone within their batches as it is found in the same areas as the other stone used to make concrete. These iron and coal are considered “soft rock.”  The reason it’s called “soft” is because they can absorb more water than other types of stone.  That water absorption can pop the concrete above the stone causing a “popout.”

Once the stone is exposed the chemical reaction between the rock, water and air causes the stone to rust until it fully degrades.  These can leave bleeding rust marks on a driveway for months.

Although they are unsightly they are not considered an unacceptable condition by industry standards.  That is unless they cover a large portion of the driveway.  These soft rocks will not impair the usability of your driveway and can be easily cleaned with some CLR.  If you would like to reduce the chances of stones like this creating popouts you can seal your driveway, and even if a popout and rusting has occurred, cleaning the area and resealing can reduce the chances of continual rusting.   

Alternatively the stones can be removed and the areas patched by a concrete contractor, noting that any concrete repairs may not match the original color of concrete exactly.

For any further questions regarding iron ore staining on driveways please consult the Alberta Government Performance Guide 2.22.

2. Concrete and Fertilizers

Flowers and plants are a simple and easy way to decorate any outdoor space and make it look attractive. While some plants require minimal maintenance and care, others require fertilizers to help replenish nutrients and promote plant growth.

Fertilizers and plant foods contain metals and minerals, such as magnesium, iron, copper and zinc. When minerals come into contact with water while on a concrete surface, the chemical reaction between them and the water can causes rust looking stains. Unfortunately fertilizer stains cannot be removed with water due to the minerals’ non water-solubility. 

Many hardware stores sell solutions that claim to remove the stains, however the chemicals in the solutions might harm concrete’s structure and cause spalling or deterioration. To ensure the concrete doesn’t get stained, avoid preparing the fertilizer solution on any concrete areas and spray around any concrete edges very carefully.



3. Oil Stains


Oil stains are the most common type of stains found on driveways and garages. Contrary to popular belief concrete is not a solid material, it is in fact porous. When oil or any other fluid hits the surface of the concrete, it begins to slowly penetrate deep into the concrete layers, leaving a stain that is very difficult to remove. In order to prevent a stain, it is crucial to use an absorbent immediately after the leak occurs on the concrete surface.

Protect the look of your concrete investment and avoid accidental spills in addition to sealing all outdoor concrete surfaces annually to prolong the look and quality of your concrete.