Edge sanding is the part of a floor sanding job most likely to show its mistakes after coating. Halo marks — the visible circular shadow around the perimeter of a floor — and swirl patterns from the edger disc are two of the most common complaints after a coat goes on. Both are preventable with the right technique and abrasive sequence.
Why Edges Are Different
The edge of a floor gets treated differently to the field in almost every way — different machine, different scratch pattern, different grit sequence, different operator pressure and speed. The result is a zone that can absorb finish differently, show a different scratch profile under raking light, and appear as a darker or lighter band at the perimeter once coated.
Add to this the fact that edge sanding is physically harder, done at awkward angles, and often rushed toward the end of a long day — and the conditions for halo marks are set up.
The Most Common Causes
1. Grit Mismatch Between Field and Edge
If the field finishes at P80 and the edge finishes at P60, the coarser edge scratch absorbs more finish and shows darker. If the edge finishes at P100 and the field at P80, the finer edge may absorb less and show lighter. The final grit must be consistent across the entire floor.
Always finish the edge at the same grit as the field's final pass. Work through the same sequence — just adjusted for the edger tool rather than the main machine.
2. Swirl Marks from the Edger Disc Not Being Worked Out
Rotary edger discs leave circular scratch patterns by nature. If these aren't worked out before final prep, they're visible under coating — especially under raking or low-angle light.
After edger work, the circular scratches must be hand-scraped or worked with a random orbital detail sander to break them up and blend the scratch into the field pattern. This step gets skipped when jobs are rushed — and it shows.
3. Operator Speed and Pressure
An edger pressed hard and moved slowly cuts deep and leaves heavy circular marks. Keep the machine moving. Let the abrasive do the work at consistent pressure rather than forcing it with body weight.
4. Wrong Grit Sequence on the Edger
Jumping too far between grits — for example, going from P40 straight to P80 on the edger without a P60 pass — leaves deep scratches that the finer grit can't fully remove. The scratch from the coarser grit shows through. Work through the sequence without large jumps.
The Right Abrasives for Edge Work
Quality edger discs make a significant difference to how cleanly you can work through a grit sequence at the edge. Cheap discs cut inconsistently, load up quickly, and leave uneven scratch patterns that are hard to work out.
Sand-Aid stocks a range of edger disc options — including SIA and Hermes discs in multiple sizes and grits — suited to different edger machines and floor conditions. The right disc for the job is one that:
- Cuts consistently across the full face of the disc
- Doesn't load up quickly on dusty or pitchy timbers
- Holds its cut rate through a full floor rather than dropping off partway through
If you're getting inconsistent results at the edge, the abrasive quality is often the first thing worth reviewing.
Pre-Coat Check
Before applying any primer or finish coat, check the edge zone specifically:
- Use a strong raking light — torch held at a low angle along the floor surface — to reveal any remaining swirl marks or grit inconsistencies
- Run your hand across the edge zone. It should feel the same as the field — consistent scratch, no raised grain
- Check where the edger zone meets the field pass. This transition line should be invisible — if it's visible as a line or shadow, more blending is required
Spending an extra 20 minutes on the edge check before coating is faster and cheaper than a recoat or a dispute with a client over visible halos.
After Coating: When Halos Appear Anyway
If a halo appears after the first coat, the options are limited:
- If it's a primer coat, it may be possible to lightly screen and reapply primer at the affected area before top coating — but this only works if the halo is from absorption difference, not scratch mismatch
- If it's after the finish coats, the floor needs to cure fully and then be assessed for spot correction or full recoat
For abrasives, edger discs and all the consumables for a floor sanding job, Sand-Aid stocks a full range from our Toronto NSW warehouse. Get in touch for trade pricing.