How to Seal & Paint Masonry Board Siding

Using a medium bristle scrubbing brush and a solution of detergent and water, wash the masonry board siding clean of mildew, dirt and grease stains. Start at the top of the siding installation and work across and down in individual courses.

Remove any crumbling fiber cement from the masonry board using your fingers and a hand brush. Remove all peeling paint and paint blisters with the scrubbing brush.

Use a low pressure jet wash and rinse the siding surface to clean off the detergent solution, cement dust and paint flakes. Work from the top of the siding installation and across in sections and down to the bottom course. Allow 2 days of sunny weather to dry the masonry board.

Use cement-based putty and a putty knife to fill in any holes created by crumbling cement. Use the putty knife to recreate the surface texture of the masonry board siding so that it blends in with the surrounding siding texture effect. Allow the putty to dry.

Seal the masonry board siding with a 100 percent acrylic paint primer. Use a stir stick to mix the primer before applying it to the siding. Using a paintbrush apply the primer to any exposed surface of the fiber cement including the top, side and bottom edges. Allow the acrylic primer to dry according to the label.

Use a stir stick to mix the latex acrylic paint to a consistent color. Using a paintbrush, apply the paint across the masonry board in full courses from the top of the installation to the bottom. Allow at least 2 hours for it to dry.

Apply a second coat of latex acrylic paint over the masonry board siding in the same way as before. Make sure that you paint all top, bottom and side edges along with the front face of the siding to complete the seal-and-paint project.