Scrape off all the loose and peeling paint on the wall or ceiling with a stiff putty knife.
Apply chemical stripper to the area with a paintbrush. Allow sufficient time to pass while the chemical agent reacts with the paint. Scrape off the remaining paint, until the underlying surface can be seen.
Soak a sponge in water and sponge off all chemical residue. Allow the area to dry thoroughly. Spray the prepared area with stain-blocking primer until the entire surface is sealed. Allow the primer to dry thoroughly.
Pour 1 gallon of semigloss paint into a 5-gallon bucket. Hang the paint-roller screen from the inner lip of the bucket.
Paint all of the wall and ceiling corners with a paintbrush 4 inches out from the corners.
Load the 3/8-inch roller nap with paint by dipping it repeatedly into the bucket, then rolling off all excess on the roller screen. Roll the walls and ceiling of the bathroom in an up and down fashion. Apply a second coat if needed.