On The Surface

How do you get rid of scratches on a windshield?

September 1, 2005

Q:
My boat has a Plexiglas windshield that has become scratched. Is there any way to remove these scratches? ' Sandy Crispin, Beaufort, N.C.

A:
Clear plastic glazing materials are subject to scratching, because they are 'soft' materials compared to safety glass. It is possible to make scratches disappear by restoring the optical properties of the surface of the plastic material. Sometimes, a coat of paste wax will fill the scratches sufficiently to make them almost invisible. It's not a permanent repair, but may be sufficient in some cases.

Deeper scratches or large areas of scratched surface require more aggressive treatment ' but not too aggressive. The idea is to physically remove the scratches and restore the original optical properties. This is done by using extremely fine wet sandpaper and buffing compounds. The job is not too hard if you can find the right materials.

A word of warning: Practice on an out-of-the-way spot first. That way if things aren't working, you won't ruin the whole windshield.

Start by sanding across the scratches with 1200-grit wet abrasive paper. Extremely fine wet 'sandpaper' is available through stores catering to auto refinishing. Use a pliable sanding block to support the abrasive, never your fingers. 3M's No. 5526 Wet/Dry sanding block is suitable. Wet the surface with sufficient water (some people like to add a drop of dish detergent) to act as a lubricant.

Always sand in a straight line, never in circles. Apply only enough pressure to the sanding pad to see results. Work up through the grits from 1200 to at least 2000 abrasive. Take your time!

Those familiar with woodworking consider 200-grit paper as 'fine.' The wet sanding abrasives identified by grit numbers in the thousands don't feel 'gritty' to the touch. That's the key to not doing more damage. Even 400-grit woodworking sandpaper would add scratches to the soft plastic glazing.

The final step is to buff the sanded area with a finishing compound similar to 3M's 06011 Imperial Microfinishing liquid. Apply with a new buffing pad on a low-speed buffing machine. Read and follow the instructions. Follow it up with a thorough wash and rinse.

Creative people have used a surprising variety of materials to remove scratches from plastic glazing. Old-fashioned toothpaste (not today's gel products) has proven effective. Some people have found a paste made of baking soda works. Experimentation may provide some other solution. Keep in mind, however, to always test any method on a small area first. Sometimes experiments do more harm than good.

Also, plastic glazing materials often develop a condition known as 'crazing.' The whole surface is covered with a myriad of micro-cracks that look almost like spider webs. This condition usually cannot be sanded or buffed away. An application of paste wax may reduce the appearance of the crazing, but will not eliminate it.