What a sheet is made of
Klingspor describes every coated abrasive as grains held to a backing by two layers of adhesive: a maker coat that bonds the grain to the backing and a size coat that locks the grains together and resists heat. Resin bonds, it says, are heat-resistant and last longer than the older animal-glue bonds. Some sheets add a top coat of stearate, which Klingspor describes as an additive that deters loading — clogging — on soft, resinous woods and on sealer coats.
The grain
| Grain | What Klingspor says | On wood |
|---|---|---|
| Aluminium oxide | Blocky and hard; wears gradually finer in use | The general-purpose grain, from removal to intermediate sanding |
| Garnet | Very sharp, cuts fast when new, fractures to stay sharp | End grain and final-finish sanding |
| Silicon carbide | Sharp, complex and brittle; shorter-lived | Mostly finishing work, and non-wood materials |
| Alumina zirconia | Tough and sharp; needs pressure to fracture | Dimensioning wood, on machines |
| Ceramic | Porous grain; best value in removal grits 24–60 | Heavy stock removal |
From Klingspor's 'Coated abrasives basics'. Grit numbers and the difference between CAMI and P-grades are on the grit chart.
The backing
- Paper, graded by weight from A (lightest) to F. Klingspor puts A to C on sheets and light discs, D on sheets and discs, and E and F on belts. Light paper folds and conforms for hand sanding; heavy paper holds up on a machine.
- Cloth, J (light, slightly conformable cotton), X (heavy all-purpose cotton) and Y (polyester, inherently waterproof). Klingspor describes X as its all-purpose cloth for belting.
- Film and latex, which Klingspor describes as combining paper's finish with cloth-like strength, suited to wet-or-dry finishing.
Which abrasives and formats to stock, and how many grits are worth buying, is covered in choosing sandpaper.
Grit, and where to stop
Klingspor defines grit as the size of the grain, by the number of openings per linear inch in the screen it passes through: the higher the number, the finer the grain. US CAMI grades are printed as a plain number and European FEPA grades with a P; above about 220 the two systems diverge, as the grit chart shows. Which grit to stop at depends on the finish going on, and makers disagree — the figures are set out in how to sand wood. Finer is not automatically better: General Finishes warns that sanding too smoothly can reduce adhesion.
Between coats
Sanding a finish is lighter work than sanding wood. Minwax specifies #220 paper between coats of its polyurethanes, and fine steel wool as an alternative on its Wipe-On Poly; General Finishes specifies fine 220–320 foam sanding pads between coats of its water-based High Performance, and maroon non-woven pads to scuff a surface that is already finished. Stearate-coated paper resists clogging on finish, Klingspor notes. Follow the finish maker's instruction for the product being sanded.
Safety— Dust
OSHA links wood dust to respiratory illness and cancer. Sand with dust collection where you can, and wear respiratory protection; old finishes may contain lead — see refinishing furniture first.
Choosing sandpaper
- The grain for the job: removal, general sanding or final passes
- A backing weight that suits the tool — light for hand sheets, heavy for belts
- Stearate-coated paper for resinous woods and sanding between coats
- The grit sequence the work and the finish call for
- CAMI or P-grade marked on the back, and not mixed by number
- Dust collection and a respirator
Sources
Grain, backing and coating definitions are Klingspor's. Grit grading (CAMI and FEPA) is on the sandpaper grit chart and is not repeated here. No abrasive was tested for this page and no brand is ranked.
- 1.
Coated Abrasives Basics. Klingspor.
Used for: Aluminium oxide, silicon carbide, alumina zirconia, ceramic and garnet grains and what each suits; paper backings A–F, cloth J, X and Y, fibre and film; stearate as an additive that deters loading on resinous woods and sealer coats; maker and size coats, and resin bonds' heat resistance.
- 2.
Minwax Product Guide. Minwax.
Used for: #220 paper between coats of Minwax polyurethanes, and fine steel wool as an alternative between coats of Wipe-On Poly.
- 3.
Technical Data Sheet, High Performance Topcoat. General Finishes, 2019.
Used for: Fine (220–320) foam sanding pads between coats, and maroon non-woven pads for cleaning and scuffing a prefinished surface.
- 4.
Technical Data Sheet, Arm-R-Seal. General Finishes, 2020.
Used for: Sanding a surface too smoothly reducing adhesion.
- 5.
Wood Dust: Hazard Recognition. U.S. Department of Labor, Occupational Safety and Health Administration.
Used for: Wood dust's health effects.
About this guide
Written by BenchRoot Editorial. How BenchRoot sources, checks and corrects its pages is set out in the Editorial Policy. If something here is wrong or unclear, the contact page explains how to tell us.