Ask Jeff: What’s the Difference Between Hydrophobic and Hydrophilic Glass?

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Many times when you’re happily waterpoling along with the water sheeting right off the glass you’ll run into a pane that for some reason or other beads up. Beads up like your work truck after a Saturday afternoon wax job. I mean the water just runs off in thousands of little droplets and the pencil jets just cannot get any sort of coverage on that glass. No way to get a good rinse. When confronted with this glass, called hydrophobic glass, the solution is to switch over to your fanjets, and use them for your rinse. The spray pattern of the fans will allow for more coverage, and let you complete the job on these hydrophobic panes and continue working.

What Causes Glass to be Hydrophobic or Hydrophilic?

No one knows for sure what causes hydrophobic versus hydrophilic properties on glass to occur naturally. Speculation ranges from installation of tin side in or out, different levels of soil, different types of soil, pyrolytic coatings, goblins, bad luck, and voodoo curses. Reality is no on knows for sure.

Sometimes changing the surface tension of the glass helps. I have talked to window cleaners who have scrubbed hydrophobic glass with bronze wool and turned it into hydrophilic glass. Same results have been achieved by sprinkling a common cleaner like Bon-Ami powder onto their Waterfed ® pole brush, scrubbing, then rinsing well. Sometimes that seems to work as well. Always check for pyrolytic coatings and possible damage when using anything that might mar them before taking steps like this.

Hydrophobic and hydrophilic properties can be intentionally caused on glass by a number of methods, however. One way is aftermarket glass treatments. Most aftermarket treatments are applied to the glass to help minimize hard water deposits and will cause hydrophobic action, or water to bead up and roll off the glass. Some hard water mitigation treatments will cause hydrophilic properties, and the glass will sheet water.

Some glass manufacturers, most notably Pilkington, Cardinal, PPG, SGG & Nippon have used coatings mostly comprised of Titanium Dioxide on their self-cleaning glass lines to instill hydrophilic properties to the surface. The Titanium Dioxide coating uses UV rays to break down contaminants on the glass and then rain (or pure water) to rinse off soiling agents. These families of self-cleaning glass lines were supposed to take the industry by storm when Pilkington introduced them in 2001, but as yet have not really caught on – which is good news for us window cleaners.

We have a video up on YouTube of a well taken care of First Klass Window Cleaning customer that has some great examples of both types of glass – right next to each other:

Video not displaying for you? Watch it on Youtube.

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