Lay arc fiberboard sections together to create a circle on a piece of paper, and trace around the exterior of the circle.
Cut out the circle with scissors.
Position the circle template on the ceiling, and trace around it to create a circle on the ceiling.
Position drop cloth on the floor under the circle, and set up the ladder.
Pour blue paint into a tray. Dip a flat brush into the paint, wipe off the excess on treads and paint the circle on the ceiling. Let dry.
Mix 1 part glaze to 1/4 part white paint in a new paint tray to create a paint wash.
Dampen the sea sponge with water. Dip the sponge into the white glaze, and blot off the excess on a paper towel.
Dab the sponge onto the blue circle to create clouds. Vary the pressure you apply to make some clouds darker and some wispier. Let dry.
Nail fiberboard arcs in place around the sky mural to create a portal effect.