Hydrophobic coatings are designed to repel water and make the glass more resistant to dirt and grime, but they can also make cleaning more difficult. In this article, we will explain the science behind surface tension and hydrophobic coatings (sometimes referred to as self-cleaning glass), and provide tips and best practices for cleaning windows with a hydrophobic coating.
If you're unaware what this actually means when cleaning a window, you'll notice that some windows (hydrophilic) allow the water to create a sheet of water that nicely cascades down the window, whereas other windows (hydrophobic) cause the water to bead and channel down the window, making it difficult to rinse all of the glass evenly.
First, to work efficiently on hydrophobic glass, it's important to understand the concept of surface tension. Surface tension is a property of liquids that causes them to behave as if they have a thin, invisible skin on the surface. This skin is caused by the cohesive forces between the molecules of the liquid, which pull the molecules closer together on the surface than they are in the bulk of the liquid.
In the case of window cleaning, surface tension can make it difficult to clean the glass because the dirt and grime on the surface of the glass can form a cohesive layer that resists the flow of water. This makes it difficult to remove the dirt and grime when rinsing the glass with water.
Hydrophobic coatings are applied to the surface of the glass when installed and create a barrier that prevents water and other liquids from adhering to the glass. In theory this stops dirt, grime, dust and anything else from accumulating however if enough time passes as we all know - windows will inevitably get dirtier until the point that they need a good scrubbing.
To clean windows with a hydrophobic coating, there are a few things you can do to make your life easier;
Firstly, it's important to avoid using abrasive materials or tools, such as steel wool or scouring pads, as these can scratch the coating and damage the glass. Instead, use a nylon bristled brush head with pure water. If you need a little extra scrubbing power, use walnut wool or similar for it's non-scratch properties - and try it on a small corner of the glass to begin with.
Secondly, using a rinse bar will give you additional jets and coverage when rinsing, to help create that cascading sheet of water that rinses the entirety of the window.
Rinse bars can be bought as part of a brush head or as an add on with selected brush heads. Fan jets offer a similar solution however you may find that pencil jets are too direct for this type of glass.
Another important thing to consider is to clean the windows in the right conditions. This may not always be possible but if you have any flexibility, it is best not to clean windows in direct sunlight as the pure water will dry too quickly - particularly on a hot day. Ideally cleaning should be done on a cloudy day or in the shade. If there's not much you can do to avoid the sunlight, cleaning earlier in the morning might be an option.
Finally, rinsing with the brush head on-the-glass can break the surface tension resulting in the glass momentarily acting hydrophilic. Using an over-the top rinse bar and a swivelling brush head to clean and rinse all with the brush remaining in contact can help create that cascading sheet of water behind the brush as you go.
To the uninitiated, the fact that one window reacts differently than another might seem strange, and many window cleaners use the same tools across the board - working inefficiently, wasting time and wasting water.
Cleaning windows with a hydrophobic coating can be a bit more challenging than cleaning regular windows, but with the right approach and tools, it can be done effectively!