How to Repair Cracks in a Cement Board Ceiling

Cement board is a building material much like drywall in appearance. While drywall has a gypsum core, cement board has a cementitious core. Manufacturers make cement board by sandwiching cement between layers of fiberglass mesh. It has a smooth surface similar to drywall. Cement board holds up to damp conditions without soaking moisture in like drywall. Cement board is mold and mildew resistant, unlike drywall. It also has a higher fire resistance rating than drywall. Cement board is suitable for interior or exterior applications.

Medium-grit sandpaper
Latex modified mortar or joint compound with hydraulic cement
Putty knife
Trowel
Fine-grit sandpaper
Sanding block

Instructions

- 1
  Sand the cracks with medium-grit sandpaper to smooth the edges.
- 2
  Apply latex-modified mortar, also known as thin set or use joint compound with hydraulic cement as an ingredient with a putty knife. Press the thin set or joint compound deep into the cracks. Extend the compound or thin set 1/4-inch past the crack on each side of the crack with a small trowel. Make the layer as thin as possible while covering the crack completely.
- 3
  Allow the thin set or joint compound to dry fully, generally one to two hours.
- 4
  Sand the repair surface with fine-grit sandpaper attached to a sanding block to level it with the existing ceiling.

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