A patchy paint job on the ceiling is an eyesore and a waste of time.The presence of an uneven coat of paint means that there is more work ahead. Here are some possible reasons why your ceiling is not looking up to par.
One possibility is that you used a paint that was way too thin. Perhaps you purchased the cheapest grade of ceiling paint on the market or maybe you painted from a previously opened can of paint that had been watered down, thus making the paint difficult to apply.
It is also possible that your means of application was inadequate. Ceiling paint needs to be applied with a 9-inch paint roller. During this process it is vital that you have ample paint on the roller pad, when you apply the paint, and that you evenly spread the paint around the entire ceiling.
Lack of a Primer Coat
In many instances when painting over a previous paint job, a primer-sealer needs to be spread across the ceiling first. This is especially true in old houses and if don't use a sealer, then the ceiling might appear patchy afterwords.
Wrong Type of Sealer
It is possible that you used a sealer that was not designed to cover old walls or old paint. Check your product carefully before you begin and buying top of the line brands helps insure a better-looking final result.
If you are using an old roller pad, make sure that is thoroughly clean and that there is no dried paint on the roller. This may create a patchy appearance, when your task is complete.
Forgot To Wash Surface
Before painting over old paint, it is vital to wash the walls with soap and water and rinse thoroughly to remove all soap residues. Excess grease can cause a patchy finish, as can a surface that is washed with soap but not rinsed.