Hydrophobic Coating
A hydrophobic coating is a chemical treatment applied to a surface that causes water to bead and roll off rather than spreading and sheeting across it. The term derives from the Greek for "water-fearing." In exterior cleaning, hydrophobic coatings are most commonly applied to glass (where they are called glass coats, nano-coatings, or ceramic glass treatments) and to concrete and masonry (where they are called water repellents or penetrating sealers).
In depth
On glass, a hydrophobic coating functions by creating a surface energy so low that water droplets maintain a high contact angle (typically above 90 degrees) and roll off before they can deposit minerals or dry as spots. Rain cleans the glass passively instead of spotting it. The technology varies from basic silicone coatings (durable for 3-6 months) to nano-ceramic treatments (1-3 years). On concrete, hydrophobic penetrating sealers work in the pore structure, repelling water and the road salt and oil it carries, which is the primary mechanism of concrete durability protection in Wisconsin's salt climate.
How this shows up on our jobs
Our Quarterly Protective Coating Program for window cleaning customers applies a hydrophobic glass nano-coating after every clean. Customers see visibly cleaner glass between visits — rain literally polishes the windows instead of spotting them.
Services where this matters
Related terms
Polymer Sealer
A polymer sealer is a protective coating applied to a cleaned and dried surface — glass, concrete, wood, metal, brick — that forms a long-molecule chain on the surface to repel water, dirt, and staining. In window cleaning, glass-specific polymer sealers (often silicon-dioxide based, sometimes called "glass coats" or "hydrophobic treatments") cause rain to bead and sheet off, which keeps windows cleaner 2-3x longer between professional cleanings. On concrete, acrylic or urethane sealers protect against oil, rust, and de-icing salt.
Concrete Sealer
A concrete sealer is a penetrating or film-forming coating applied to cleaned, dry concrete to reduce its absorption of oil, road salt, staining agents, and water. Penetrating sealers (silane, siloxane, or silane-siloxane blends) chemically bond below the surface to repel liquid without changing the appearance or traction of the concrete. Film-forming sealers (acrylic, epoxy, polyurethane) create a surface coating that is visible as a sheen and provides excellent stain resistance but requires periodic reapplication as it wears.
TDS (Total Dissolved Solids)
TDS stands for Total Dissolved Solids — the concentration of dissolved minerals, salts, and metals in water, measured in parts per million (PPM). A TDS meter is the single most important tool in professional window cleaning because it determines whether rinse water will dry spot-free. Standard Madison tap water measures roughly 250-400 PPM, which leaves visible mineral spots on glass when it dries. For streak-free, squeegee-free results with a water-fed pole, rinse water must be at or below 10 PPM, and ideally 0-2 PPM.
Deionized Water
Deionized water — often shortened to DI water — is water that has had essentially all of its dissolved mineral ions removed by passing it through specialized ion-exchange resin beads. Positive-charge ions (sodium, calcium, magnesium) are swapped for hydrogen ions, and negative-charge ions (chloride, sulfate, bicarbonate) are swapped for hydroxide ions. The result is near-pure H2O with a TDS reading at or near zero.
Hard Water Stain
A hard water stain is the crystalline mineral deposit that forms on glass, metal, and stone when water high in dissolved calcium, magnesium, iron, or silica evaporates and leaves its dissolved minerals behind. The stain starts as a cosmetic film that rinses off easily; over weeks or months, it bonds chemically to the surface and etches into it, becoming progressively harder to remove. On glass, severe hard-water staining is technically etching — the minerals have chemically fused into the silicate surface and cannot be washed off without specialty chemistry or mechanical polishing.