How to Fix Scratched Acrylic Windows

Acrylic scratches. It is softer than glass, and a dry cloth with a grain of grit in it will leave a line you can see against the light. The consolation is that acrylic, unlike glass and unlike polycarbonate, can be sanded and polished back to optical clarity. A scratch in a glass window is permanent. A scratch in an acrylic storm window, boat hatch, RV pane, or aquarium panel is a half-hour job with the right abrasive.

This guide covers how to judge the damage, what to use for each level, the wet-sanding method that works, and the products that will leave the window worse than you found it.

First: is the panel coated?

Stop here if the acrylic has a hard coat. Abrasion-resistant marine sheet, "AR" or "mar-resistant" grades, UV-filtering greenhouse panels, and anything with a no-drip coating carry a thin surface layer. Polishing cuts through it and leaves a dull patch that cannot be fixed. NOVUS prints this warning on the bottle. If you are not sure, test a corner that does not matter, or check the product name against the manufacturer. Coated panels get cleaned, not polished; a deep scratch means a new panel.

Step 1: Judge the scratch

Wash the area with water and a soft cloth so you are not dragging grit through the test. Then run a fingernail across the scratch, perpendicular to it.

The deeper the scratch, the more material you have to remove around it to level the surface, and the larger the area you will end up working. A deep scratch on a small panel is a candidate for replacement rather than repair if the panel is cheap.

Step 2: Gather the kit

Three products cover everything. Our scratch repair kit roundup reviews them; the short version:

• NOVUS Plastic Polish 1-2-3. Number 2 is the fine scratch remover, number 3 the heavy one, number 1 the finishing cleaner. About $10 to $25; the 8-ounce kit is on Amazon.
• Micro-Mesh Acrylic Restoral Kit. Six cushioned abrasive cloths from 1500 to 6000 grit, a foam block, flannel cloths, and Micro-Gloss polish. $36.85 from aircraft suppliers, covers 30 square feet; the same kit (Micro-Mesh KR-70) is on Amazon.
• Meguiar's PlastX. A one-step gel for haze and the finest scratches. About $12 at any auto parts store or on Amazon.

Plus: a spray bottle of water, several clean microfiber or flannel cloths, masking tape to protect surrounding trim, and good light. For a gouge, a sheet of 400-grit wet-and-dry sandpaper.

Step 3: Polish-only repair (haze and lines you cannot feel)

1. Wash the panel. Grit under the cloth makes new scratches.
2. Apply a small amount of NOVUS 2 or PlastX to a clean cloth, not to the window.
3. Rub in straight strokes along the scratch, then across it, with moderate pressure. PlastX can be worked in gentle circles.
4. Wipe clean with a fresh cloth and check against the light.
5. Repeat two or three times if it is improving. If it is not improving after three passes, move up to the scratch method.
6. Finish with NOVUS 1 for an antistatic, fog-resistant surface.

Step 4: Scratch repair (nail catches)

1. Wash and dry the panel. Tape off adjacent trim.
2. Apply NOVUS 3 to a cloth and work the scratch firmly in straight strokes, alternating direction. Number 3 is a real abrasive; it will leave its own fine haze, which is expected.
3. Wipe clean. Follow with NOVUS 2 over the whole worked area, not just the scratch, until the haze from 3 is gone. Skipping this step is the most common reason people report that NOVUS "didn't work."
4. Finish with NOVUS 1.

If the scratch is still visible after one full 3-then-2 cycle, go to wet sanding rather than repeating; you will remove material faster and more evenly.

Step 5: Wet sanding (deep scratches and gouges)

This is the aircraft-canopy method and it works on any uncoated acrylic. The rules are more important than the grits.

The rules

• Everything stays wet. Water lubricates and cools; a dry abrasive melts the surface and smears it.
• Light pressure. Let the abrasive do the work.
• Alternate stroke direction with every grit change, so you can see when the previous grit's marks are gone.
• Never skip a grit. Each one removes the marks of the one before; skip one and the marks stay.
• Rinse the panel and your hands between grits so you do not carry coarse particles into the fine stages.
• Work an area larger than the scratch, feathering out, so you do not leave a dished spot that distorts the view.

The sequence

1. For a gouge only: wrap 400-grit wet-and-dry around the foam block, wet it, and sand the scratch in straight strokes until the gouge is gone and the whole area is a uniform matte. Do not go further than needed.
2. Start Micro-Mesh at 1500 for deep scratches, 2400 for moderate. Wet the cloth and the panel, wrap the cloth around the block, and sand in light straight strokes in one direction until the previous marks (or the scratch) are gone. For a deep scratch, stay at 1500 as long as it takes; this stage does most of the work.
3. Rinse. Move to the next grit, change stroke direction 90 degrees, sand until the previous grit's lines are gone. Repeat through 1800, 2400, 3600, 4000, and 6000. By 4000 the surface will start to look clear when wet; by 6000 it should be nearly clear dry.
4. Polish with Micro-Gloss or NOVUS 2 on a clean flannel cloth until the last haze is gone.
5. Finish with NOVUS 1 or PlastX.

Expect a single deep scratch on a storm window to take 20 to 40 minutes. A whole boat hatch lens is an hour or more. One pilot's review of the Micro-Mesh kit warns that an entire canopy is too much work by hand, and that rushing leaves micro-scratches. Do one scratch well rather than a whole panel badly.

What not to use

• Brasso or any metal polish. The abrasive is wrong for acrylic and leaves a haze worse than the scratch.
• Toothpaste. A mild abrasive that dulls a small area and then needs a real polish to fix.
• Ammonia glass cleaner. Crazes acrylic over time. It is not a repair product and it should not be your cleaner either.
• A power buffer on high speed. Heat softens acrylic. If you use a drill-mounted pad, keep it slow and wet.
• Any abrasive on coated sheet. See the warning at the top.
• Dry paper towels. The cause of most of the scratches you are fixing.

When to replace instead

Replace the panel when the scratch is deeper than about a third of the sheet thickness, when there are many scratches across a large area, when the sheet is coated, or when the panel is cheap enough that an hour of your time costs more. A 1/8-inch storm-window panel from a cut-to-size supplier is a few dollars a square foot; our suppliers roundup covers where to buy, and our cost guide has the prices. For a boat hatch or an RV window, the lens is the expensive part and repair is nearly always worth trying first.

Keeping it from happening again

• Clean wet, always. Water or a plastic-safe cleaner, never dry.
• Microfiber or flannel, rinsed often. Never paper towel.
• NOVUS 1 or PlastX after cleaning leaves an antistatic film that sheds dust, which is what makes the next scratch.
• On a boat or RV, a coat of polymer wax once a season helps the surface shed grit.
• Where scratching is unavoidable, buy hard-coated sheet next time and accept that it cannot be polished.

Sources

• Moleroda: How to remove scratches from acrylic with Micro-Mesh
• Aircraft Spruce: Micro-Mesh Acrylic Restoral Kit
• NOVUS Plastic Polish: 2 oz kit and International Association of Penturners: Not entirely happy with Novus
• Meguiar's PlastX
• ShunPoly: Can Brasso remove scratches from plastic
• Truck Camper Adventure: Dometic Seitz window review, maintenance tips
• ACRYLITE: Acrylic sheet vs glass, Taber abrasion data