Sandpaper Grit: Selection for Surface Preparation
Quick answer: Grit numbers describe abrasive particle grading. Within a given system, higher numbers generally indicate finer particles. Select the grit to suit the substrate and coating instructions.
What is sandpaper made from?
Abrasive particles are bonded to a backing such as paper, cloth, film or fibre. The abrasive and backing affect flexibility and suitability for the task.
Abrasive materials
Aluminium oxide and silicon carbide are common examples. Garnet, zirconia alumina and specialised abrasives are also supplied for particular applications. Check the abrasive manufacturer’s information rather than choosing by material name alone.
Dry and wet sanding
Use water only with a product approved for wet sanding. Silicon-carbide particles alone do not establish that the backing is waterproof. Before coating, clean and dry the surface to the product requirements.
Grit numbers and grading standards
FEPA P and CAMI are grading systems; do not assume their numbers are equivalent without a reliable comparison. Grit is not simply the number of particles on one square centimetre.
ISO 6344-2:2021 addresses P12–P220, while ISO 6344-3:2021 addresses P240–P5000 within their defined scope for coated abrasives. Grit numbers are not the same as measured surface roughness or a steel cleanliness grade.
Grit ranges in the reference standards
| Reference | Grit range | Scope |
|---|---|---|
| ISO 6344-2:2021 | P12–P220 | Macrogrit grading |
| ISO 6344-3:2021 | P240–P5000 | Microgrit grading |
These ranges do not recommend a particular grit for a job. Select the required grit for the actual substrate and coating. Grit number is not abrasive hardness or measured surface roughness.
Selecting an abrasive before coating
- Identify the substrate and existing coating.
- Choose grit and preparation method to match the coating data sheet.
- Check compatibility of the abrasive, powered tool and intended task.
- Remove residual dust and contamination before application.
Sanding does not replace every preparation method. If the specification requires blast cleaning, hand sanding is not automatically equivalent.
Read the paint data sheet guide and explore marine paints.
Discuss the substrate and project conditions with Armani Fam to select a preparation method compatible with the specified coating.
