How to Sand Acrylic and Plexiglass (And Polish It Clear Again)

Acrylic — sold as Plexiglas, Perspex, Lucite or just “plexiglass” — is genuinely lovely to work with once you understand two things about it.

It scratches very easily. A dry cloth on a dusty sheet is enough. That is why acrylic panels, display cases and machine guards look tired so quickly.

It also polishes back completely. Unlike glass, acrylic is soft enough that you can sand scratches out and restore full optical clarity. A badly scuffed sheet can be made to look new, which is remarkable when you first see it happen.

The enemy in both directions is heat. Friction softens acrylic, and softened acrylic smears, gums up abrasive and clouds. That is why almost all acrylic sanding is done wet. 💡

Acrylic vs Polycarbonate — Know Which You Have

These get sold side by side and treated as interchangeable. They are not, and it matters here.

Why it matters: this guide works for acrylic. Polycarbonate often carries a factory hard coating for scratch resistance, and sanding straight through that coating leaves an area that will never match — it stays hazier than the surrounding sheet, and polishing does not recover it. If you have coated polycarbonate, replacing the panel is often the honest answer.

How to tell them apart: acrylic has a slightly higher-pitched ring when tapped and snaps cleanly if you break an offcut. Polycarbonate flexes and resists breaking. Sheet is also usually marked on the protective film.

Acrylic forgives you because it can be polished. Coated polycarbonate does not, because you cannot polish a coating back once it is gone.

Why Heat Ruins Acrylic

Acrylic is a thermoplastic. It softens when warm, and it does not need much.

Friction from sanding generates heat locally at the abrasive. On acrylic that means:

• The surface softens and smears instead of being cut cleanly.
• The abrasive clogs with melted material, which increases friction, which creates more heat — a loop that gets worse fast.
• The surface clouds in a way that is far harder to polish out than ordinary scratches.
• Thin sheet can distort permanently.

The controls are simple:

1. Wet sand. Water carries heat away continuously. This alone solves most of it.
2. Low speed if using any powered tool.
3. Light pressure. Pressure equals friction equals heat.
4. Keep moving. Never dwell in one spot.
5. Touch test. If the acrylic feels warm, stop and let it cool.

Crazing, and the Products That Cause It

This is the failure mode people cause accidentally, often before they even start sanding.

Crazing is a network of fine cracks that appears in the surface of acrylic. It looks like frost or a spider’s web, it scatters light badly, and — importantly — it cannot be polished out. The cracks go into the material, not just across the surface.

What causes it: chemical attack, usually combined with stress in the material.

• Ammonia-based glass cleaners — the classic mistake. Never use standard window cleaner on acrylic.
• Solvents — acetone, alcohols, many degreasers and brake cleaners.
• Some adhesives and tapes, especially their solvent carriers.
• Stress from over-tightened fixings, which makes chemical crazing far more likely.

Does the Scratch Need Sanding at All?

Work through this before reaching for abrasive — the same escalation logic as with scratches in wood.

1. Clean it properly first. A lot of “scratched” acrylic is actually dirty or hazed with residue. Mild soap, soft microfibre, no pressure.
2. Fingernail test. Run a nail across. If it glides over, the mark is shallow and polish alone will remove it. If it catches, you will need abrasive.
3. Try polish first. A plastic polish with a mild cutting action removes light scratches without any sanding.
4. Only then sand, starting with the finest grit that will touch the scratch.

The golden rule: start finer than you think. Every grit you use creates scratches you then have to remove, so beginning at 400 when 800 would have worked doubles your work for no benefit.

The Grit Ladder

Acrylic needs a long, fine ladder and you genuinely cannot skip steps — every remaining scratch shows because the material is transparent.

The milky stage is normal. At 600 to 1000 grit the acrylic will look completely opaque and you will be certain you have ruined it. Keep going. The transparency comes back between 2000 grit and the polish — exactly as with epoxy resin.

Step by Step, Start to Finish

Step 1 — Clean the sheet properly

Mild soapy water and a soft microfibre. No glass cleaner, no solvents. Rinse and let it dry. Any grit left on the surface will be dragged across it.

Step 2 — Assess the damage

Fingernail test each scratch. Decide the finest grit that will actually touch the deepest one.

Step 3 — Support the sheet

Acrylic flexes. Lay it on a flat, clean, padded surface so it cannot bow while you work — flexing while sanding gives an uneven result and can crack thin sheet.

Step 4 — Set up wet sanding

Bucket of clean water with a drop of dish soap, waterproof wet-and-dry paper soaked beforehand, a rubber or foam backing block, and a spray bottle.

Step 5 — Start at your chosen grit

Keep the surface flooded. Work in straight strokes in one direction with light, even pressure.

Step 6 — Change direction 90 degrees at each grit

This is how you know a grit is finished — when no scratches remain running the previous direction. On transparent material this is the only reliable check.

Step 7 — Wipe and inspect constantly

Squeegee the slurry and look through the sheet against a light. Rinse the paper often and change the water when it clouds.

Step 8 — Work up through every grit

No skipping. Each pass is quick because you are only removing the previous scratches.

Step 9 — Dry and assess

The surface should have an even satin haze. Any remaining deeper scratch means going back a grit — polish will not hide it.

Step 10 — Polish through the stages

Heavy cut, then fine, then final shine. See below.

Step 11 — Protect it

A plastic-safe protectant or anti-static polish helps resist the next round of scratches and reduces dust attraction.

Polishing Back to Clear

Polishing is not optional and it is where the transformation happens.

Plastic polishes come in graded stages, and using them in order matters:

1. Heavy cut — removes fine sanding scratches and light scuffing. This is the stage that does the work.
2. Fine cut — refines what the heavy stage left, removing its own finer marks.
3. Clean and shine — final gloss, and usually adds a light anti-static protection.

By hand: apply a small amount to a clean soft cloth and work in small circles with firm pressure. Buff off with a fresh cloth. Repeat with the next stage. Hand polishing works well on small pieces — picture glazing, display boxes, instrument covers.

By machine: a polisher with a foam pad is much faster on large sheets. Use a low speed, keep the pad moving, and check temperature constantly. A polisher can heat and haze acrylic faster than sanding can.

Use a fresh cloth for each stage. Carrying heavy-cut compound into your final polish just puts the scratches back.

Edges and Flame Polishing

Cut acrylic edges are usually rough and opaque from the saw. There are three ways to deal with them.

Sanding and polishing — the same ladder as a face, working along the edge. Slow but completely controllable, and it gives an excellent result. Keep the block flat so the edge stays square.

Scraping — drawing a sharp blade or scraper along the edge at a shallow angle shears off the saw marks quickly. A traditional technique that gets you to a near-polished edge fast.

Flame polishing — briefly passing a flame along the edge melts the surface smooth and makes it transparent. It gives a beautiful result in skilled hands and it is easy to get badly wrong: too slow and the edge distorts and bubbles, and the process introduces internal stress that makes the edge more prone to crazing later, especially near solvents or adhesives. Practise on offcuts before trying it on anything that matters.

What not to do: do not try to polish an edge with a power buffer at speed. The concentrated contact area heats up almost instantly.

Common Mistakes (and How to Fix Them)

Mistake 1 — Cleaning with glass cleaner

What happens: ammonia crazes the surface permanently, and crazing cannot be polished out.
The fix: use a dedicated plastic cleaner or mild soapy water only.

Mistake 2 — Dry sanding

What happens: heat softens the acrylic, it smears and clouds, and the paper clogs.
The fix: wet sand everything, keeping the surface flooded.

Mistake 3 — Starting too coarse

What happens: you create deep scratches you then have to remove through six more grits.
The fix: start with the finest grit that touches the damage. Often 800 is enough.

Mistake 4 — Stopping at 1000 grit

What happens: a permanently milky panel and the belief it is ruined.
The fix: continue to 2500 or 3000, then polish. Clarity comes at the end.

Mistake 5 — Skipping grits

What happens: deeper scratches survive and show clearly after polishing.
The fix: no skipping, and change direction 90 degrees so you can see progress.

Mistake 6 — Sanding with bare fingers

What happens: finger-shaped dips, very visible in a transparent sheet.
The fix: always use a backing block.

Mistake 7 — Overheating with a polisher

What happens: the surface hazes or distorts.
The fix: low speed, constant movement, frequent temperature checks.

Mistake 8 — Sanding coated polycarbonate

What happens: you remove the factory hard coat and the area never matches again.
The fix: identify the material first. Coated polycarbonate usually means replacing the panel.

Pro Tips Worth Knowing

Leave the protective film on as long as possible

Acrylic ships with a peel-off film for good reason. Cut, drill and fit with it in place, and remove it only at the very end.

Test on an offcut

Run your whole process on a scrap first. You learn how the material responds and how long each stage takes.

Work with light behind the sheet

Holding acrylic up against a light source shows remaining scratches far more clearly than looking at it face-on.

Use two buckets

One for soaking clean paper, one for rinsing, so coarse grit never contaminates your fine sheets.

Anti-static polish reduces future work

Acrylic attracts dust electrostatically, and dust plus wiping is what causes most scratching. A protectant genuinely reduces the cycle.

Do not over-tighten fixings

Stress in the sheet makes chemical crazing far more likely later. Use oversized holes and let acrylic expand and contract.

The Polish I Recommend

Since polishing is what actually restores clarity, a graded plastic polish system is the product worth having.

Frequently Asked Questions

Your Final Checklist

• Material identified — acrylic, or coated polycarbonate
• Sheet cleaned with plastic cleaner or mild soapy water, never glass cleaner
• Fingernail test used to judge scratch depth
• Polish tried before any abrasive
• Sheet supported flat so it cannot flex
• Waterproof wet-and-dry paper soaked in advance
• Rubber or foam backing block used — never bare fingers
• Surface kept flooded throughout
• Started with the finest grit that touches the damage
• Direction changed 90 degrees at every grit
• No grits skipped through to 2500 or 3000
• Acrylic checked by hand and kept cool
• Paper rinsed often, water changed when cloudy
• Inspected with light behind the sheet
• Polished through heavy, fine and shine stages
• Fresh cloth used for each polish stage
• Machine polishing kept at low speed and constantly moving
• Anti-static protectant applied at the end
• Protective film left on until the job is finished

Related reading: how to sand epoxy resin, wet sanding vs dry sanding, and the complete sandpaper grit chart.