Textured paint should be used as a design element and not as a technique to cover up sloppy workmanship or imperfections in the wall. The ability of a textured paint to hide flaws in the wall surface is minimal. The value of textured paint comes with the coarse appearance of the final product along with the ability of the uneven surface to diffuse artificial light and soften acoustics.
Inspect the wall surface for any depressions or cracks in the surface. Fill any holes with spackling paste and cracks with white silicone caulk.
Sand any rough spots including spackling paste applied in Step 1 with medium-grit sandpaper. Fully complete and sand any new sheetrock before beginning to paint.
Wash old walls with a sponge, soap and water, and then rinse with cold, clear water. Be sure the walls are completely dry before you apply the primer-sealer.
Put down a dropcloth and then cover the walls and sheetrock with a water-resistant latex primer-sealer. Check the manufacturer's specifications to ensure the primer-sealer is compatible with the textured paint.
Let the primer-sealer dry for at least 24 hours.
Apply the textured paint with a heavy roller pad and an extension pole. Use a paint brush to cut in around the edges. Since textured paint is very thick, it is best to apply a little bit at a time; when you do apply the paint, spread the paint out so it doesn't build up. With texture already added to the paint, build-up can be a problem.
Check the manufacturer's specifications (for the textured paint) to see if a topcoat is needed; add a top coat (if necessary) of non-textured semigloss latex paint to cover the texture.
Add texture to latex wall paint or purchase textured paint with the texture already added. You can paint just the ceiling with textured paint, or paint the whole room. If mould is present on the old walls, remove it with bleach and water. Unfinished sheetrock requires a special primer for sheetrock. Texture paint does not hide many mistakes, but it does break up the light a bit, so they aren't as noticeable.
Don't take any shortcuts with the sheetrock finishing, if you plan to cover the area with textured paint. Sheetrock plaster can be applied to bathroom walls with a roller or trowel after the walls are primed to create texture. Once the plaster dries, another coat of paint is added. This is an advanced technique that has some benefits and drawbacks.