Vehicle Water Spots: Why Ceramic & Graphene Coatings CAN’T Prevent Them

Proof that Ceramic or Graphene Coatings cannot prevent hard water spotting from sprinklers with heavy mineral water.

By Christopher Brown of

Most automotive ceramic or ‘graphene’ ceramic coatings feature hydrophobic water behavior. This is the ability of a surface to quickly and effectively shed water. Extreme water behavior is great feature of ceramic coatings and has become a huge auto detailing and car care industry selling point due to the positive benefits of the ‘self-cleaning effects’ and ease of washing aspects coatings provide.

While ccoatings are a valuable and helpful protective ally in the fight against topical contamination and hard water damage– they are by no means a magical savior.

This is because paint is engineered as a Thermal Elastic Structure. The elastic nature of paint allows it to expand and contract with the demands of varying temperatures- most importantly heat. Heat sources include both environmental & mechanical. If automotive paint was not thermally elastic then it would be brittle, break, and create micro fractures which would lead to failure and delamination over time.

A characteristic of this thermal elasticity is a porous structure. Therefore, it is automotive paint’s extremely porous structure that causes it to be vulnerable to contamination or damage from the minerals contained within, or transported by, water or other liquids.

The resin system (the binder and backbone) of any ceramic, or graphene oxide (rGO) ceramic, coating is the main mechanism providing additional ‘protection’ vs. mineral deposits. However, these generally do not act as a spackle and plug up the porous paint structure. Instead, quality coating formulas work within the paint’s matrix and add enhanced protection. However, they are so small (nano scale) that they cannot (nor should they) fully take over the characteristics of automotive paint.

Remember Ceramic or Graphene Coatings are designed to work WITH a Paint System’s Characteristics — NOT in their place.

The Problem with Many Ceramic or Graphene Coating Marketing Claims

The main issue with some automotive coating marketing are the claims. These claims are either direct stated and or implied. Generally,the claim, promise, or inference is that ceramic or graphene coatings will prevent mineral deposits on paint from liquids.

Regardless of:

  • marketing claims
  • advertising campaigns put forth by detailing chemical companies and or detailers:

Automotive Ceramic or ‘Graphene’ Coating formulations, including hydrophobic properties, cannot guarantee full protection against vehicle surface water spotting.

Because, well…. NO-THING Can.


One Word: Science

The scientific fact is this:

The minerals (mostly calcium & magnesium) contained within water will deposit themselves into automotive paint, if allowed to sit on paint long enough.

This is because the primary factors that most influence:

  • the creation of 
  • and vulnerability of vehicle surfaces to

water spotting are much greater contributing factors than what a surface’s topical protection is.

It’s simple uncomplicated science, yet the information is seldom discussed. This is because many manufacturers and businesses prefer to market coatings as a surface solve-all type of solution– WHICH THEY ARE NOT.

Hydrophobics Help Protect Against Hard Water Spots– THEY DON’T PREVENT THEM 

Hydrophobic properties allow automotive ceramic coatings the ability to:

  • help keep vehicles clean for longer
  • allow them to quick and easily shed water
  • enable very quick and simple car washing

These beneficial attributes aid in vehicle enhancement and functional lifestyle benefits. For deeper information into the science behind hydrophobics, please reference the article: How Ceramic Coatings Work: Detailing Hydrophobic Science Explained.

The positive attributes of a ceramic coating’s hydrophobic properties (contact angle and slide angle) primarily occur when a vehicle is in motion–air moving water. Essentially, hydrophobics assist in moving water or contamination off surfaces as fast as possible to help eliminate damage from occurring.

But, even the best coating, featuring the most insane water behavior, cannot combat mineral deposits if the vehicle sits still and water dries on surfaces.

Gravity greatly enhances the chance of water falling off vertical panels. However, horizontal panels, those parallel to the ground – which are often flat or concave – are not so fortunate. Horizontal panels, especially on a stationary vehicle, are immune to gravity and have no means of shedding water. This leaves them much more susceptible to water drying on the surface and depositing minerals.

Therefore, it is CRICITCAL to NEVER allow standing water to sit and dry on vehicle surfaces.

The Dangers of Hard Water Spotting to Vehicle Surfaces

Sure, water spots are unsightly blemishes upon finishes, particularly on darker colored vehicles. However, the potential chemical hazards of water spotting are of far greater concern than displeasing white markings.

If water contains a high concentration of minerals and harsh chemical contaminants it may inflict great harm upon vehicle surfaces. Combined with automotive paint that is on the vulnerable end of the spectrum, and issues such as deep etch markings, discoloration, and precursors to rust (oxide contamination) may occur.

This happens because the water acts a transport mechanism, moving contamination into porous automotive paint systems.

If water spots occur and the vehicle’s paint repeatedly heat cycles (heats up and cools over many days, weeks, or months), the water spotting may seep further down into the paint. Because, when the matrix of paint is fully swelled open by heat — at its most vulnerable point– any minerals contacting the paint have the greatest likelihood to sink further down into the paint. The minerals may also fuse themselves into the heart the paint’s chemical matrix.

This is why, upon first detection of water spots, it is critical to IMMEDIATELY wash the vehicle.

This will likely remove any new minerals sitting on top of a paint system, which haven’t had enough time to fully fuse into the paint.

Scientific Explanation of How Vehicle Water Spots Form

Hard water spots occur when water dries on a surface. When the water evaporates, mineral deposits are left behind. Seems simple enough—but there’s a bit more to it.

If a vehicle remains stationary, and water partially or fully dries on the surface, nothing can be done to prevent the minerals from penetrating into the paint.

Sometimes the panel is hot before water contact, and other times the panel heats with water already on top. If a vehicle panel’s temperature is cool during water contact, then water spotting may not occur. However, if the surface temperature is HOT at the time of water contact, then the likelihood of spotting drastically increases.

This is because, on a hot panel, the water evaporates quickly and automotive paint’s porous structure is swollen open and reaches maximum vulnerability. Either way, if the vehicle panel is cold or hot, there is always the potential of minerals seeping DEEP into the paint porous structure, often past fully cured ceramic coatings.

When the paint’s pores are open fully, minerals and other chemical contamination can very easily stick to and embed themselves within the vehicle finish. So, when water evaporates from a hot panel, the minerals are left behind and embed themselves into the paint. Sometimes lightly, other times moderately, and sometimes DEEPLY into the paint. This all depends on the type of minerals, concentration levels, along with other chemical agents present (within the water or on the surface) at time of water contact. These points are discussed in more detail later on.

Some common minerals contained within water, such as calcium and magnesium, are extremely alkaline. A high concentration of calcium in water may cause etching to some paint systems. The depth of the etching depends on the type of minerals, the overall concentration levels of these minerals, and the length of time those corrosive mineral agents dwell on top and within the paint.

Defining ‘Hard Water’ Mineral Measurements

The term “hard” or “soft” water refers to the level of minerals concentrated in water. Typically the minerals that harm automotive surfaces are Calcium and Magnesium. 

The concentration of minerals in water is measured in milligrams per liter (mg/L) or PPM – parts per million. Often these numbers are publicly available for reference from local water utility officials. Otherwise, a simple water hardness test strip kit will quickly reveal the approximate level of dissolved minerals contained in any water source.

The classifications of water types are as follows:

  • Soft: 0-17mg/L (ppm)
  • Slightly Hard: 17.1-60mg/L (ppm)
  • Moderately Hard: 61-121mg/L (ppm)
  • Hard: 121-180mg/L (ppm)
  • Extremely Hard: 180mg/L (ppm) and Higher.
  • RIDCULOUSLY HARD: Las Vegas, NV is 270 ppm. Some Cities in Arizona and the Rocky Mountains regularly read 450-550 ppm +!

3 Automotive Water Spot Creation Variables

Vehicle Paint Chemical Formulation

The FIRST variable majorly influencing whether a vehicle is more or less prone to the formation of hard water spots is the paint’s chemical formulation.

Think of it like spaghetti sauce staining a linen shirt. IF the color of a cotton shirt has low pigmentation, say white, then it is already vulnerable. The chances of removing the stain completely depend on the amount of time the densely pigmented red sauce is allowed to dwell and bond to the cotton fabric of the shirt.

If the sauce is removed within moments, then possible staining it is relatively easy to fully remove.

However, if the sauce is undetected and allowed to fully seep into the cotton and fully dry at the bottom of the laundry basket for a week, then good luck.

Some automotive paint systems are similar to various types shirt materials in terms of their vulnerability.

Some paint systems contain a low amount of solids and therefore are more vulnerable to the effects of heat and chemical contamination. On the other hand, some paint systems contain a high solids content offering far greater protection overall.

Water’s Mineral & Chemical Makeup and Concentration Levels

The SECOND group of factors influencing water spotting are the water’s mineral and chemical composition and their concentration levels.

The ability to create Damage via Water Spotting or Chemical Damage to paint systems is directly linked to:

  • A) The types and combinations of minerals and chemical contaminants contained within the water.
  • B) The concentration levels of those minerals or chemical contaminants within the water.

Heat of Surfaces at Time of Water Contact

The THIRD variable of water spot creation is HEAT.

More specifically, the temperature of vehicle panels and/or the environment’s ambient temp during water evaporation.

Heat acts as a catalyst to the paint system causing more vulnerability– therefore magnifying the impact of the waters mineral concentration. If a panel is already HOT, say 140°F (~ 60°C) or higher before water contact, that is the worst recipe for quick and deep water spotting.

In direct sun exposure, with atmospheric temperatures between 95°F and 110°F (35-43.5°C) panels can routinely reach surface temperatures of 190-212°F (87-100°C).

In these extreme conditions, the paint is most vulnerable. This is because heat has swollen the porous paint structure to a fully open state. Therefore, any water contact to these HOT surfaces results in near instant water evaporation. This essentially injects the minerals and chemicals contained within the water directly into the paint’s porous structure.

Even if a car isn’t in direct sunlight, ambient environmental temperatures of 95°F(35C) or higher will still cause paint swell and heighten the chances of water spot creation with water contact.

Therefore, the combination of:

  • A) a vulnerable paint system
  • B) mineral and chemical heavy water
  • C) HOT vehicle panels

equals a surefire chemical recipe for disastrous hard water spotting.

Some automotive paint systems are so vulnerable to chemical agents that ceramic coating enhancements may only slightly improve the overall chemical protection.

For additional info on Heat & Automotive Paint Systems, Read the OCDCarCare article– Detailing Paint Correction: Paint Swelling & Heat Explained.

Vehicle Water Spot Protection Strategy

No current paint system or paint treatment, including ceramic coatings, may guarantee complete protection against water spotting.

There is no solve all water spot prevention method for automotive surfacesNo Matter What Certain Coating Manufacturers or Detailing Companies Claim.

It’s just a impossibility within the known physical universe we inhabit– as long as Automotive paint remains a dynamic porous structure.

The best ‘prevention’ or protection against vehicle hard water spotting is a STRATEGY.

If water is not allowed to dry on a vehicle’s surface, then water spotting may be avoided completely. Additionally, using mineral free water during car washes (including Waterless and Rinseless wash methods) will ensure vehicle surfaces remain unspotted.

De-ionizing filtration systems remove most all minerals and deposits from water such as calcium, sodium, iron, copper, and sulfates.

11 Tips to Avoid Automotive Hard Water Spots on Automotive Surfaces

1)  DON’T Let Water Dry on Automotive Surfaces: Remove Water from Surfaces as Soon as Possible

2)  Only Wash Vehicles with Cool Surfaces

3)  Avoid Car Washing in Direct Sun. Wash Vehicles in Shaded Areas Only

4)  Immediately Dry Vehicle After Washing

5)  Avoid Parking Near Sprinklers or Irrigation Whenever Possible

6)  If Incidental Water Contact Occurs, Dry Panel ASAP

7) If Vehicle is Dirty and Rain Occurs, Wash Vehicle ASAP

8)  Purchase a Water Softening System or De-Ionizer for Car Washing

9)  For Waterless or Rinseless Car Washing: Mix Solution with Distilled Water

10)  If Hard Water Use is Necessary: Wash Vehicle in Early Morning or Late Evening

11)  In SUPER HARD Water Areas: Apply a Topical Spray Sealant (same Product Line) on Top of Coating for Added Protection

Vehicle Hard Water Spot Removal Techniques:

Upon first detection of water spotting, immediately wash the vehicle to remove the maximum amount of minerals possible from surfaces.

Timing is crucial here and is generally the best and easiest line of defense. Often times, a thorough car wash will remove light or freshly made water spots by cleansing the surfaces and of hard mineral deposits before they set up deep inside the paint system.

Stubborn Water Spot Removal Methods After Washing

Upon first detection of water spotting, immediately wash the vehicle to remove the maximum amount of minerals possible from surfaces. If washing does not entirely remove water spots then move to spot treating areas with an acid based solution to loosen and remove mineral deposits. Make sure the solution is safe for the surfaces with water spotting, because many acids can be uber aggressive and ruin plastics, rubber, trim, or even etch glass.

If you do not have a dedicated detailing water spot removal product then you may use distilled white vinegar. The vinegar’s acidity works to break down and loosen a light to medium concentration of common minerals for removal with a microfiber towel.

Apply the vinegar liberally to a microfiber towel and then apply evenly to water spots. Allow vinegar to dwell for 2-4 min. Then gently wipe at the spots with the microfiber towel. If spots are stubborn, apply a second time and allow the vinegar to dwell 6-8 min before wiping.

If Vinegar alone does not work, there is another household trick to boost cleaning power. Try mixing in some fresh juiced and strained lemon juice with the vinegar in a 50/50 ratio. Apply the mixture and allow it to dwell for 2-3 Minutes before wiping with a microfiber towel.

For a heavier concentration of water spots allow the mixture to dwell for 4-6 min, then liberally apply more vinegar mixture to a microfiber towel before wiping the spots with light to medium pressure.

For stubborn or heavier mineral deposit removal, a dedicated automotive water spot removal product may be necessary. The majority of these are heavily acidic in nature, therefore make sure to wear full PPE (personal protective equipment) such as: goggles, gloves, and a respirator during use. Also, take caution to ONLY apply the product to surfaces indicated as safe on the product label.

NOTE: After any acidic surface treatment, make sure to thoroughly flush all panels with water or a waterless wash solution to neutralize the acidic treatment.

Removal Method for Etched and Deep Set Hard Water Spots

Some hard water spots cannot be removed via topical treatments. This is because enough minerals, of a strong type, have penetrated far enough into the paint system to etch the paint system.

Paint Polishing may be the only action for removal of this severe level of hard water spotting. These are identified by their: visibly extremely heavy mineral deposits, ultra deep position within the paint’s structure, or even by mild to severe surface etching.

Often a light paint correction is enough to remove many water spots. However, the more severe and concentrated the spots– the more aggressive the polishing necessary. For best results, seek out a local reputable detailer to perform such services. After the removal of hard water spots, make sure to reapply the topical protection that matches the remainder of the vehicle panels. 

If water spots were detected immediately after ceramic coating application, the problem may be a different sort of water spot issue completely. This removal procedure was explored in a previous OCDCarCare Los Angeles Detailing Article:  Phantom Waterspots Appearing After Ceramic Coating Application.

Wrap Up: Water Spots and Automotive Ceramic Nano Coatings

Automotive Ceramic and Graphene Ceramic Coatings, depending on their chemical composition, offer the best current protection for vehicle surfaces against contamination and water spots. This is due to their increased solids content, chemical protection, and hydrophobic properties.

However, Ceramic Nano Coatings are NOT a solve-all savior of surface protection. And they should not be sold in such a fashion to uneducated vehicle owners.

Sure, some ceramic or ‘graphene’ coating manufacturers may even outright claim their products prevent water spots.

Don’t believe the marketing speak of over-hyped protection.

The proof is in science and in the information explaining the practical aspects of how coatings function to protect paint and vehicle surfaces… Information some coating manufacturers either don’t understand themselves or don’t want you to know, understand, or investigate.

“ALWAYS Keep Learning to Strengthen Your Passion & Your Business.”

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For more auto detailing and car care related topics please browse: OCDCarCare Los Angeles’s – Auto Detailing Article Archive

Christopher Brown
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