Good question ‘how to clean walls before painting’! You need to wipe of several things from your walls before painting commences!
Washing Your Walls
The fact that surface dirt can lead to very poor adhesion makes using a light soap to wash off soiled surfaces very necessary. These surfaces include those that are often touched, or has some oily deposits from cooking. Make sure the soap does not leave any residue behind.
Wash all trims and doors, especially where they are often handled. Wipe all surfaces using a damp cloth once the surfaces are clean enough. Make sure the wall dries before painting commences.
Getting Rid of Pen, Water Stains, and Crayon
Preparing a wall for painting requires using liquid soap to get rid of all marks made by crayons, pens, water stains, etc. Use a neat wet cloth for wiping. If any mark remains after the wiping exercise, use Fresh Start or Moore's QD 30 to stop the finished coatings from bleeding.
Dull Glossy Areas
To make sure there is effective adhesion, use sandpaper and sand all glossy surfaces. Remove all sanding dust. Clean all surfaces using vacuum cleaning and wipe using a tack piece of cloth.
Examine the floors, walls, and all ceiling surfaces for traces of nail holes, cracks, or any such surface flaws. Rake out all large plaster opening or hanging particles in your ceilings and walls using a putty knife.
Press some spackling compounds firmly into all crevices using the putty knife and smoothen it out until the spackling compound and the surfaces are of the same flush.
To fill up mitered open connections and window or door trim that is separate from your walls, press the compound firmly into all crevices, and smoothen it using your finger. Leave it to dry before sanding lightly.
Apply the patching compound twice for the best results since patching compounds shrink when they dry.
Getting Rid Of Loose Paint
Remove scaling or loose paint using a putty knife. When you get rid of paints from ceilings and walls, fill the paint edges to make sure surfaces are smooth. This will blend the two paint levels to make the edges unnoticeable after re-coating. When getting rid of paint from doors, trim, or sash, make use of a fine sandpaper for sanding the whole surface.
So above are how to clean walls before painting and what you should remove from your walls. Hope everything goes on well with your repainting!