The short answer
The rule of thumb is simple: the higher the grit number, the finer the paper. Coarse paper is used for removal, fine paper for smoothing and matting. For most interior work, you work from coarse to fine, and you do not jump straight from very coarse to very fine. So choose the grit based on two things: what your material is and at what stage of the work you are.
The grits in a row
A handy overview of the grit ranges and what you use them for:
- Coarse, approximately P40 to P80: removing old, thick or loose paintwork, sanding wood firmly, working out rough imperfections. This is heavy sanding and it leaves scratches, so always follow up with finer.
- Medium, approximately P100 to P150: leveling filler and imperfections, smoothing wood for the primer, preparing a rough surface.
- Fine, approximately P180 to P240: matting a glossy layer, light intermediate sanding, and smoothing just before the finish layer.
- Very fine, approximately P280 to P400: fine intermediate sanding for paint and varnish, lightly roughening a smooth surface.
- Ultra fine, P400 and higher, often wet sanded: beautifully finishing high gloss and varnish and making very fine corrections.
Why the right grit is important
Sanding is a balance. If you use too coarse a paper for a fine phase, you will create scratches that you will later see under your paint or varnish, because a thin finish layer does not mask those grooves. If you use too fine a paper for coarse work, you will sand yourself silly without results, because the paper removes nothing.
That is why you work in steps. You start with a grit that is coarse enough for the job, and you work up to finer until the surface is ready for what comes next. Do not skip too many steps, as the scratches from the coarse grit will remain visible. Jumping from P80 straight to P240 leaves marks; working from P80 via P120 to P180 does not.
The grit also depends on your material and your goal. Removing old paint requires something different than preparing a wooden door for varnish or matting a wall for a new coat of emulsion paint. So first determine what exactly you want to achieve, and choose the grit accordingly.
Step by step
- First determine your task and your material. Do you want to remove something, level it, mat it, or finish it, and is it about plaster, filler, wood, old paint, or varnish? That together determines your starting grit.
- Then choose a starting grit that matches the heaviness of the work. Heavy removal starts coarse, light matting or finishing starts fine. If in doubt, you prefer to start a bit finer and go coarser if it is too slow, as this avoids unnecessary scratches.
- Then work up to finer in reasonable steps. Each subsequent grit removes the grooves of the previous one until the surface is smooth enough for your finish.
- Use a sanding block or a sander for flat areas, so you remain flat and do not sand in dips. For profiles, mouldings, and round shapes, work with a flexible sanding sponge that follows the shape.
- Dust off between the steps and especially at the end. Sanding dust that remains disrupts your next grit and later the adhesion of your paint.
- Stop at a grit that matches what is going on top. For a matte wall paint, you don't need to go as fine as for a high-gloss varnish. Then you prime or paint.
The mistake you should avoid
The biggest blunder is using too coarse paper in the fine phase. The scratches you make then do not disappear under a layer of paint or varnish, but show through, especially with gloss and side light. Always work fine enough for the finish.
A second pitfall is skipping too many steps to finish faster. Jumping from very coarse straight to very fine seems like a time saver, but the coarse scratches remain visible and you end up spending longer on touch-ups. A few grits in between really makes a difference.
What you need for this at PrepKing
Good sanding starts with having the right grit at hand, and preparation is what PrepKing is all about. With us, you will find sandpaper in a complete range of grits, from coarse for removal to fine for finishing, a sanding block for flat surfaces, a flexible sanding sponge for profiles and mouldings, and a dust mask for safe working.
No sales talk, just the right paper for the job at hand. Every surface, every time.
Related: how to sand a wall before you start painting, how to sand filler flat neatly, and for the professional how to keep dust nuisance manageable when sanding in a lived-in renovation.
