The speed with which a painter can complete the job will determine its final cost, but time is difficult to estimate. Some painters have more experience and cover a wall faster, but some are more methodical and take more time. Most painters should be able to cover about 100 to 120 square feet of flat surface in an hour, unless they are working on a very large wall. Wood or plaster might reduce that amount to 80 to 100 square feet. You should also consider the time required for a first coat to dry before a second coat may be applied. This will add time as well -- anywhere from one to 48 hours depending on the paint.
Thorough preparation is essential to ensure a good finish. Contractors might have to fill cracks or holes and remove old paint if it is badly worn, peeling or flaking. They remove all paint and apply a suitable primer to the bare surface. If the existing paint is in reasonable condition, they clean it and rub it with abrasive material to provide a key for the new paint. On new surfaces, such as bare wood or fresh plaster, they apply a suitable seal, followed by a primer coat.