Ask Jeff: What’s the Difference Between Hydrophobic and Hydrophilic Glass?
Many times when you’re happily water poling along with the water sheeting right off the glass, you’ll run into a pane that for some reason or other beads up. I mean, the water runs off in thousands of little droplets, and the pencil jets just cannot get any coverage on that glass. There’s simply no way to get a good rinse. When confronted with this glass, called hydrophobic glass, the solution is to switch over to fan jets and use those for your rinse. The spray pattern of the fans will allow for more coverage, 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 or hydrophilic properties. 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. The reality is no one 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. The 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 along these lines.
However, hydrophobic and hydrophilic properties can be intentionally caused to glass through various methods. 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 caught on – which is good news for us window cleaners.
We have a video 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:
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