Sandpaper-What grain size for the sandpaper?

Sandpaper-What-grain-size-for-the-sandpaper

Sanding wooden surfaces – what grain size for the sandpaper?

Sandpaper is available with different grit sizes: from very coarse with 40 grit to very fine with 320 grit. There is a suitable grit for every application. Below you will find out what grit the sandpaper should have when sanding wooden surfaces and how to achieve an even surface.

Different grits

Abrasive grains are industrially manufactured. The individual grain sizes are screened out with the help of sieves. A coarse grit should sand away a lot of wood and not wear out too quickly. A fine grain, on the other hand, should ensure an even sanding pattern.

Good sanding performance can only be achieved if the abrasive grains on the sandpaper are all the same size. With fine sandpaper, even one grain of sand that is too large would cause many ugly scratches. This is an important reason to only buy high-quality sandpaper. Irregularities in the granulation are virtually impossible here.

 

Scuff marks from 40 grit paper next to scuff marks from 80 grit paper

Scuff-marks-from-40-grit-paper-next-to-scuff-marks-from-80-grit-paper
Scuff-marks-from-40-grit-paper-next-to-scuff-marks-from-80-grit-paper

Gradually from coarse to fine grit

In the beginning, traces of processing such as bumps, material tears, pencil marks, and glue residue are removed with an 80 grit. (You can learn how to remove edit marks here.)

The coarse sandpaper leaves scratches, which are ground out with finer sandpaper. You work your way from the rough to the fine. A sensible sequence is, for example,

Types-of-Grit-sandpaper
Types-of-Grit-sandpaper
  • 60 Grit – Coarse
  • 80 Grit – Coarse
  • 100 Grit – Medium
  • 120 Grit – Medium
  • 150 Grit – Medium
  • 180 Grit – Fine
  • 220 Grit – Fine
  • 520 Grit – Ultra-Fine

One should keep the distance from one grit to the next rather small. For example, jumping from 80 grit paper straight away to 150 grit paper takes more time than adding one or two grit sizes (100 and 120) in between.

Sand with little pressure and change the sandpaper immediately when it becomes dull. Sandpaper is dull when the removal noticeably decreases. Applying pressure now to get something out of it doesn’t make sense. You only press the wood fibers into the surface and thus create an uneven sanding pattern.

Material tears, glue residue, and pencil marks are sanded away with 80 grit sandpaper.

On the back of the sandpaper, you will find an imprint that refers to the abrasive grain size. Shown here is an 80 grit. The number 80 is preceded by a ā€œPā€. The “P” indicates that the number refers to the abrasive grit size.

Uniform surface

Especially at the end of the sanding, you should make sure that you have sanded every spot with the corresponding grit. If you have sanded one area with a coarser grit than the rest of the area, the wood sucks differently there. If the wood is stained later, clearly visible color differences are the result. Change the sandpaper in good time, especially for fine sanding with 150, 180, and 220 grit. If you have used blunt sandpaper in some areas and sharp sandpaper in other areas, this will also lead to color differences. Different grain accentuation effects also occur when painting and oiling the surface if sanding is irregular.

How finely does a wooden surface have to be sanded?

At the end of the grinding, the question arises as to which grit you should stop with. For example, if you stop with 150 or 180 grit, you’ll finish faster and save sandpaper at the same time. This is possible when sanding by hand. However, one should finally check whether the surface feels sufficiently smooth.

With orbital sanders and random orbit sanders, you should always use up to 220 grit to avoid “sanding rings”. Coarser grits leave hardly any visible squiggles when machine sanded, but these become visible after the surface treatment.

If a surface is to be waxed or oiled, it is advisable to sand it particularly finely. The natural surfaces are so thin that you can feel every rough spot. Here you grind both with the machine and by hand up to 220 grit.

If the first application has dried on oiled surfaces, you should sand finely in between. 320 grit is recommended if the surface is to be particularly fine. For simpler surfaces, 220 grit is sufficient.

Tip:

If you are not sure how finely you should sand, make a surface sample. This is particularly useful for larger projects or when using particularly valuable materials. This minimizes the risk of a major loss of time or material.

Grinding disc for an eccentric grinder with a 125 mm grinding disc diameter. The grit is very fine with P 320.

Eccentric-grinder-with-a-125 mm
Eccentric-grinder-with-a-125 mm

For oiled surfaces, an intermediate sanding with 320 grit ensures a smooth surface that is very pleasant to the touch.

Section old paintwork

320-grit-ensures-a-smooth-surface
320-grit-ensures-a-smooth-surface

Coarser sandpaper-like 40 grit is only needed if you want to sand off old paintwork. It is often necessary to sand off several layers of paint, as old furniture has been painted over again and again. To do this, you enter with 40 papers. The layer of lacquer is sanded down until wood can be seen. Then sand it down with 80-grade paper. The 40-grade paper would cause deep scratches on the wood.

When sanding off old paintwork, work at a reduced speed. This avoids the generation of excessive frictional heat. Too much heat will cause the sandpaper to clog prematurely.

My advice:

make sure you have good dust extraction too. Dust reduces the grinding performance. In addition, old paint often contains heavy metals. Better not to inhale these.

40 grit sandpaper is good for sanding down old paintwork.

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