How to Sand a Wall Before Painting? (Key Tips)

In many new constructions, including remodels, having a uniformly smooth wall prior to paint application is a must for an aesthetically pleasing appearance. One of the most noticeable aesthetic aspects in a space, in order to project a clean, modern, and tidy environment are the walls, their texture, shape, and color.

To bring an innovative look to the walls, you can completely change the look of the room simply with new paint, to achieve this, however, it is necessary that the surface is smooth and uniform.

Sanding a wall before painting sounds like a super easy and simple task, but if you don’t follow a careful technique it could become a tedious and complicated task, and in the end, you run the risk of doing a bad job.

Sanding is one of the processes in which there are many secrets when it comes to preparing a wall and surfaces in general, whether they are walls, wood, or metal.

For the process of sanding a wall, it is essential to know the different types of sandpaper that will be required to sand the surfaces to be worked.

Basically, sandpaper can be divided into 4 groups:

  • Grinding sandpaper
  • Water-based sandpaper
  • Wood sandpaper
  • Wall sandpaper

Each of these groups of sandpaper can be subdivided into coarse and fine sandpaper, depending on the intensity and type of smooth finish to be given to the surface to be sanded.

Next, I will explain the process of how to sand a wall properly, which sandpaper to choose, and some tips and tricks to do an optimal job, but first I will explain the basic preparations before sanding.

Although they are very basic preparations, on many occasions they are not taken into account.

Is it necessary to sand the wall before painting?

Sanding a wall before painting is not a mandatory process, especially if you have surfaces with a good smooth finish, but, in order to have a professional finish it is always advisable to sand the walls, especially in works where the walls have been spotted or soiled with different materials.

If there is a lot of dust on the walls, there is a risk that it may affect the adhesion of the applied paint.

As a general rule, walls should be sanded before painting if you have one of these defects:

  • Cement spots
  • Arid roughness
  • Irregularity in the plaster
  • Remains of other paints
  • Remains of stickers

Proper preparation before sanding the wall

So that you do not have more work than before after sanding the walls, proper preparation is essential.

First of all, thoroughly clean the room and cover the door and window hinges. Sanding dust is very fine and gets into every crevice, no matter how small.

Door and window frames and sockets should also be taped well, and ceiling lights should be protected. Furniture that cannot be removed should be wrapped in an airtight plastic or something that can be covered to avoid being soiled with dust.

Create a stable base on which you can work safely. Ideally, a platform should consist of two ladder racks, between which you will place a sturdy wooden board on which you can safely stand.

Use support in which you can work comfortably and safely vertically in the highest spaces of the walls, this can be a double support painting ladder.

It is essential to wear protective clothing: protect your eyes and respiratory tract with suitable protective masks and goggles. Wall grinders can also be very noisy during operation, so it is also necessary to wear hearing protection.

Children or pets should not be in the room while sanding. Also, warn all roommates that the room in which you are working should not be entered without protection.

If necessary, use some light source that illuminates the wall at an inclined angle of 25 degrees, this allows a better understanding of the progress of the work thanks to the incidence of light, remember that sanding a wall should be considered detail work.

Which sandpaper to choose for sanding the wall?

To know the type of sandpaper suitable for sanding the wall it is necessary to define the types of sandpaper available, usually, the sandpapers are classified by numbers according to the type of sanding they can provide, the higher the number, the smoother the sanding.

GRAIN TYPE OF SANDPAPER WORK
from 40 to 60 very coarse roughing, removal of paints and varnishes
from 80 to 120 coarse smoothing, removal of very coarse sanding marks
from 150 to 180 medium smoothing removal of marks from coarse sanding
from 220 to 240 fine finishing sanding between coats
from 280 to 320 very fine very fine finish, removal of surface stains
from 360 to 600 super fine super fine finishing, removal of gloss on surfaces
from 800 to 1500 extra fine polishing smoothing of surfaces

 

The most commonly used sandpaper on walls prior to a paint application is the medium-coarse finish, in number classification 80, this type of sandpaper is sufficient to polish the remains of impurities and loose material from the wall prior to painting.

The idea is that after applying the 80 grit sandpaper on the wall and removing all the impurities, you should pass a medium smooth sandpaper, between 120 and 150, to remove any marks left by the medium-coarse sandpaper and leave the surface of the wall much smoother.

Sanding walls by hand without using equipment

Hand sanding is very common and in many cases necessary in situations of awkward corners and spaces, but, on flat surfaces such as walls, the idea is to use a wooden block as a support, it can be a small piece of 2 “x4” that fits comfortably in your hand.

Using a piece of wood as a backing will allow you to hold the sandpaper perfectly and sand effectively. For sanding difficult places (moldings, etc.) it is usual to find a piece of molding that fits in the place to be sanded and proceed as before (fix the sandpaper with staples). A sanding sponge can also be used.

The technique of using a wooden block as a support for the sandpaper is also widely used in carpentry.
The technique of using a wooden block as support for sandpaper is also widely used in carpentry.

When sanding surfaces the correct way to pass the sandpaper is in circular movements, never use vertical and horizontal movements when sanding, if you pass the sandpaper in straight movements the surface runs the risk of being very scratched and marked.

Using the right sanding machine for wall sanding

Choosing the right wall grinder depends on the project and the needs. Many wall grinders are very heavy and noisy.

You work more quietly with a hand sander that is operated with muscle power.

Special models of sanders can be connected to a suitable industrial vacuum cleaner so that the sanding dust is sucked up directly.

The use of machinery is not mandatory, the wall should be sanded by hand, especially if you work on small areas or only want to smooth the wall selectively.

If in addition to the wall you want to sand other surfaces, such as the wooden floor, and you also want to remove adhesive residues from tiles and carpets, it is advisable that you use a device with a wide field of application, such as the Bosch wall sander, that brand is one of the best and personally one of my favorites.

Should you wash the walls before or after sanding?

Although professional painters do not usually wash the walls before painting, washing the walls before painting is recommended, and this is done right after sanding the wall.

The idea is to remove any accumulated dust and dirt, leaving the wall as clean as possible for the application of the paint, most walls can be washed with a sponge and warm water, in case of dirty walls with grease, water, and detergent are required to remove the grease.

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