Removing scratches from acrylic glass

Plastic glasses (such as acrylic glass ) are superior to real glass in many respects. They are easily deformed, lighter in weight and do not break as easily as glass. But the surfaces can scratch . Luckily you can polish the material.

depth of the scratches

You see a scratch because it forms an interface that is not in the same plane as the rest of the surface. The light breaks differently on this than on the rest and the reflection is also different. Polishing means that you remove the disruptive interface. You achieve this by removing the surrounding material. So you adjust the surface to the indentation of the scratch .

Above a certain depth, you would have to remove a lot of material to make the scratch invisible. There is also a risk of polishing a dent in the material . Although this unevenness is less clearly visible than a scratch, the wavy surface is very annoying. This is especially true when the acrylic glass surface covers an image or writing. There is a magnifying glass effect in some places, so the letters appear irregular.

There is no guide value for how deep a scratch can be, which you can easily polish out. Run your fingernail gently over the surface. If you can feel the scratch, it's too deep to polish.

Replenishment is sometimes possible

Light-curing acrylic-based adhesives are perfect for filling deep scratches . The agents have an almost identical refractive index and do not attack acrylic glass. There is therefore no risk of the material becoming cloudy, as can happen with solvent-based adhesives. But to be on the safe side, you should always do a test in a hidden spot.

The adhesives require UV light to cure and should be covered with offset foil or foils for laser printers during curing. If you cannot expose the part to the sun, you will need a UV lamp.

Adhesives with a very low viscosity are perfect so that they can flow well into the damage.

1. Put a drop on the repair area and cover with a piece of foil.
2. Cure the glue with UV light for a few minutes.
3. Peel off the foil.
4. Carefully run a scraper blade over the repair area.

Now you need to polish the entire disc.

Toothpaste or special polish?

You will always find instructions on the Internet on how to polish an acrylic glass pane with toothpaste . This method is certainly cheap, but the result is rarely satisfactory. It usually makes professional polishing more difficult because additional scratches can occur.

The art of polishing is the correct removal of material . Coarse abrasive particles remove a lot of material, but they leave marks. Very fine abrasives will hardly remove any material, but they are good at removing the marks left by the coarser abrasive.

There are three arguments against toothpaste:
- The hardness of the grinding particles is matched to teeth, not to plastic.
- You don't know how coarse the abrasive particles are.
- You cannot polish gradually from coarse to fine.

Abrasive pastes in block form , which are available in different grades, are perfect for acrylic glass.

What to polish acrylic glass with

You can polish by hand or with an electric grinder . Do not use belt grinders, angle grinders or rotating grinding machines, but a so-called random orbital polishing machine . The polishing wheel moves in an elliptical path instead of rotating. This prevents you from leaving circular polishing marks.

When choosing the polishing disc, follow the instructions provided by the polishing agent manufacturer. In tests, he has determined which material you can use to achieve the best result.

The polishing process

Machine polishing

Important: Hold the sanding pad straight so that it does not tilt.

1. Start with coarse polishing paste .
2. Put some on the buffing wheel.
3. Set a low speed to spread the paste on the acrylic glass without applying pressure.
4. Increase the speed. Move the polishing pad in horizontal tracks with light pressure. The tracks should overlap about halfway.
5. Repeat step 4 but now ride vertical lanes .
6. Switch to a finer polishing paste and start with step 1.

Hand polishing

The processes are identical to polishing with the machine. Use a soft cloth instead of a buff.

Perform circular movements along the tracks. Avoid circling in one spot multiple times.

Whether polishing by hand or with a machine, never apply excessive pressure and always work in trajectories across the entire wheel . Do not try to apply special treatment to the areas with the scratch.