How to prep fascia board for painting

Latex paint takes about 24-36 hours to cure in normal/optimal (50%) humidity environments, and longer to dry if your humidity is higher. The easiest way to bring down household humidity in the summer is to leave your A/C cranked down. Your air conditioner will remove humidity from the air.

First, ensure that any patching you do has dried thoroughly. Prime the day before you paint. Put a fan on it and make sure that you don't use the shower for about six to 12 hours after priming.

Don't use the shower for at least 12 hours after you paint. Then keep the room ventilated (which might mean showering with the door open and a fan blowing drier air in), and keep your A/C turned down so that your relative humidity stays lower.

Painting over older existing paint, especially gloss finish, requires preparation. The two things that most interfere are surface contaminants (such as grease, dust, other deposits) and lack of tooth (too smooth a surface).

On your new sections, cleaning the painted surface with soap and water or with a solvent cleaner (like mineral spirits) will generally solve the first problem. Light sanding (usually about 120 grit), followed by cleaning with mineral spirits or wiping with a tack rag will generally solve both. There is also a mild chemical stripper called a deglosser that roughens the surface somewhat like sandpaper.

Just painting over an older glossy paint will often lead to poor adhesion. The section already done is not easily fixed except by sanding and cleaning to remove any of the new paint that is still loose and to roughen up the exposed old paint. Then follow with a new coat of fresh paint.