Blue Stains on Tile


Nick Valenti

 October 11, 2022. 8:51 PM

blog-blue-stains-on-tile-discolorationAre the tiles in your bath, shower, shower head, or faucets turning blue? What causes this discoloration and where does it come from? In most cases, blue/green stains are caused by the water flowing through your copper piping having a low (acidic) pH. Chances are your plumbing fixtures are connected to copper pipe, and the blue / green water stains are the result of the insides of the copper pipes being attacked by the aggressive low pH (acidic) water.

The Chemistry Behind Blue / Green Stains on Tiles

To better understand, pH is the measure of acidity in water. Below is the pH scale which ranges from 0 to 14, with 7 being absolute neutral. Any measurement below 7 is acidic, any measurement above 7 is alkaline. If the pH of your water supply is 6.8, it is considered “aggressive,” which can lead to copper corrosion and can damage metal pipes, faucets and fixtures. Blue stains begin to appear when the pH of the water is 6.8. To further add insult to injury, each 0.10 of a point is exponentially more aggressive, causing significantly greater metal corrosion, than the number before it. Determining pH can be done by simply performing an on-site pH test, which can be purchased from most local hardware stores or online.

Water Hardness - Table of Classifications

grains per gallon (gpg)milligrams per liter (mg/L) parts per million (ppm)U.S. Geological Survey ClassificationWater Quality Association Classification
< 1.0< 17.1softsoft
1 to 3.517.1 to 60softslightly hard
3.5 to 7.060 - 120moderately hardmoderately hard
7.0 to 10.5120 - 180hardhard
10.5 +180 and oververy hardvery hard

For instance, if your water tests show a pH level of 6.5, you may not be too alarmed because it’s only a few points away from 6.8. Right? Unfortunately, this is a big mistake. Water with a measured pH of 6.5 can cause considerable damage over time, eventually causing serious problems with metal plumbing in your home, and other household appliances, like water heaters, dish washers and ice makers.

Although acidic pH water is the most common cause of blue / green tiles, the opposite effect, or too much alkalinity, can also have damaging effects, such as clogged pipes and fixtures, or slow running faucets. Blue or green stains can be removed from tiles but only temporarily, unless the source cause is determined and repaired.

Removing Blue or Green Stains on Tile with Ease

blog-blue-stains-on-tile-copper-pipesTo remove blue stains from tile, we recommend applying a heavy-duty cleaner specifically designed to remove cleanly without damaging your surrounding tile, such as MAPEI’s UltraCare Acidic Tile & Grout Cleaner. Mix with equal parts water and apply the solution to the affected area. Allow it to stand for 5-10 minutes. Once complete, apply UltraCare Abrasive Surface Cleaner to the area and scrub using a white scrub pad or soft, nylon bristle brush. Rinse with clean water and dry with a clean towel. Do not apply this solution to acid sensitive natural stones such as marble, travertine or limestone. Always test first in an inconspicuous area.

For natural stone use MAPEI’s UltraCare Heavy Duty Stone, Tile & Grout Cleaner and UltraCare Abrasive Surface Cleaner.

These are general instructions; be sure to follow the application instructions on the respective products’ Technical Data Sheets and Safety Data Sheets carefully. Reach out to our Technical Services department at 1-800-361-9309 if you have any questions.

Products mentioned in the article

UltraCare Abrasive Surface Cleaner
UltraCare Abrasive Surface Cleaner
Abrasive Surface Cleaner UltraCare Abrasive Surface Cleaner is a powerful, abrasive cleaner that is safe for use on a variety of ceramic,…
UltraCare Heavy-Duty Stone, Tile & Grout Cleaner
UltraCare Heavy-Duty Stone, Tile & Grout Cleaner
UltraCare Heavy-Duty Stone, Tile & Grout Cleaner is a highly concentrated and high-alkaline cleaner and degreaser. This product is…
UltraCare Acidic Tile & Grout Cleaner
UltraCare Acidic Tile & Grout Cleaner
UltraCare Acidic Tile & Grout Cleaner is a highly concentrated acidic cleaner formulated to remove cement grout haze, mortar residue,…


Nick Valenti

Nick Valenti

Nick joined MAPEI in 2012 as the technical expert for the UltraCare line. He has more than 25 years of experience in the sealers and cleaners product line. While his experience includes an in-depth knowledge of products, Nick also understands the major issues and problems that can arise with the surfaces to be protected and has solutions for these challenges. In charge of training MAPEI’s Sales and Technical Service teams, Nick is even more importantly the in-the-field resource for MAPEI’s customers and end users.


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