Maintenance
Scratches, chips and cracks: what can be repaired and what cannot
Some damage is a ten-minute polish and some is a new part. The distinction is depth and location, not the size of the mark.
Maintenance
Some damage is a ten-minute polish and some is a new part. The distinction is depth and location, not the size of the mark.
A damaged acrylic part is either a surface problem or a structural one. Surface problems are cosmetic and can be polished. Structural problems — chips, cracks, crazing, anything at a fixing point — cannot be repaired to the original strength, and for a guard or a barrier that means replacement regardless of how it looks.
| Damage | Repairable? | Method or verdict |
|---|---|---|
| Scratch not felt with a fingernail | Yes | Wet-sand 800 → 1500 → 3000, polish with cerium oxide |
| Scratch felt with a fingernail | Partly | Can be polished out but leaves a slight lens; acceptable on a non-critical face |
| Deep gouge | No | Polishing removes too much material; the surface becomes visibly dished |
| Scuff or haze over a large area | Usually | Machine polish at low speed; risk of distortion on thin sheet |
| Chip on a hidden edge | Cosmetically | Can be dressed back; the part loses a little dimension |
| Chip on a visible edge | No | Re-cut and re-polish, or remake — a dressed edge on a polished panel shows |
| Crack from a fixing hole | No | Replace, and change the fixing detail or it will recur |
| Crazing (fine white network) | No | Material damage below the surface; replace |
| Broken corner | No | The corner cannot be rebuilt invisibly |
| Delamination in a bonded joint | No | Cut apart and re-bond, which usually means remaking the parts |
The mistake people make is starting with a polish. Polishing removes material very slowly, so on anything deeper than a haze it takes hours and leaves an uneven surface. Start with the finest grit that removes the scratch, and work down.
Do not use a dry machine polisher on acrylic. Friction heat softens the surface and the pad drives the softened material, producing a wavy distortion that is far more visible than the original scratch. If a machine is used, keep it slow, keep the pad wet, and keep it moving.
A chip is a stress concentration. On a panel held in a frame, or one that sees thermal cycling, a chip on the edge is where a crack will start, and the crack will travel across the part. This is why a chipped edge on a machine guard is a replacement, even if the chip is small and on the back.
On a display piece that sits on a shelf and is never loaded, a small chip on a hidden edge can be dressed back and used. The judgement is not about the size of the chip; it is about whether the part carries any load or sees any movement.
A crack in acrylic does not stop. The tip of the crack concentrates stress, so every temperature cycle, every knock and every load pushes it further. Repairing a crack with solvent or adhesive closes the visible line but does not restore the material, and the crack continues from the tip or restarts alongside the repair.
On a non-structural, non-safety part a crack can be stabilised — a small hole drilled at the crack tip stops it travelling — but this is a holding measure to keep a display in service, not a repair. On a guard, a barrier or anything structural, the part is replaced.
Polishing labour is skilled and slow. On a small simple part, remaking is usually cheaper than an hour of hand polishing, and the result is a new part rather than a repaired one. Polishing makes economic sense on a large panel, a part with machining on it, or a part where the alternative is a long lead time.
Ask for both prices. We quote a repair and a remake on the same drawing whenever a customer sends a damaged part, because the answer is not always the one they expected.
It is a mild abrasive and will polish a very light haze on soft acrylic, but it is inconsistent and leaves a patch if the area is not worked evenly. A proper 3000-grit paper followed by cerium oxide gives a predictable result for a few pounds of material.
No. A heat gun softens the surface and can close very fine surface marks, but it also distorts the panel, re-introduces stress and can leave a visible gloss patch. It is not a repair technique on a visible face.
It stops the crack travelling, which is a valid holding measure on a non-structural part. It does not restore strength and the hole is visible. On a guard or a barrier this is not an acceptable repair.
It is labour, so it scales with area and access. A small local repair is a fraction of the part cost; polishing a whole 1,200 mm panel is often more than remaking it. We quote both so the comparison is explicit.
It can be bonded, but the joint will be visible, the corner will be weak, and on a clear panel the bond line shows. For a display or a guard, the part is remade.
A photo under raking light plus a note on where the part sits is usually enough to give a straight answer and both prices.