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Using a rain repellent

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A rain repellent is a special product that is designed to be applied on glass. The product leaves a very hydrophobic layer on top of the glass. Water won’t be able to form any wetting, and the round beads are more easily blown off the glass.

Why use a rain repellent

A rain repellent creates a safe situation. When there is so much water on the screen that your wipers hardly do the trick anymore, the rain repellent will create a hydrophobic layer that prevents the water from creating one big sheet. Because of this, it is easier to look through the window. When driving above a certain speed the wind will actually blow those drops off the windscreen. Some people have reported saying that they hardly needed their wipers anymore. However, when wipers need to be used, it is safer to just use them. Rain repellent or not.

The effect

Effect of a rain repellent
Effect of a rain repellent

A rain repellent has a hydrophobic effect. This simply means that the water molecules pull harder on themselves then that the surface underneath pulls on them. This gives the impression that the water is being pushed away. This effect causes the water to not being able to form big sheets of water. Instead it forms individual round drops of water. These drops are more easily affected by wind because they are higher with a much smaller contact area. If the vehicle reaches a certain speed, the waterdroplets are simply blown off the surface.

Application

Application varies from product to product. But in most cases this general guide will give a good idea on the most common way of application.

  • Clean the window as best as you can
  • Polishing/claying can help you to clean the glass more thoroughly
  • Wipe the glass off with an IPA based glass cleaner
  • Apply the glass sealant either to an application pad or a MF towel
  • Apply the product to the glass. The key is to apply it evenly on the surface
  • If you put a few small dots in several places, and then go over that area criss-cross, you are more likely to get an even coverage
  • Leave the product to dry (check the label or ask your manufacturer on the recommended time)
  • Buff off the residue, in many cases this will take a fair bit of effort
  • A glass sealant doesn’t really need any maintenance, just a regular wash is enough
  • Check the finished result in different light, there might be smear that are difficult to see

Ups and downs

There are a few upsides and downsides on using a rain repellent.

  • It won’t fix worn wipers
  • It can make the wipers skip a bit
  • The drops of water can dry up and leave little round spots of sand/dust
  • Not everybody likes the look of raindrops flying over the windscreen
  • Application can sometimes require a fair bit of effort (product dependent)
  • The cheaper sealant will only last months, the more expensive coatings can last years
  • Cleaning thoroughly can have a big effect on performance
  • In very rare cases people have reported seeing a very slight funhouse-mirror effect (others couldn’t replicate it)
  • The product can have a negative effect on the MF towel used, it’s best to use an old MF towel
  • Certain product are known to dissolve foam applicator pads

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