How to Fix Right Angle Ceiling Cracks in Walls

Brush across the crack with a thin paintbrush, dipping into the crack as much as possible with the bristles to remove dust and loose bits of wall from the crack. If working in a concrete or cement wall, angle a flathead screwdriver into the crack and tap it softly to break away the material from inside of the crack until the interior of the crack becomes slightly wider than the surface opening. Brush across the crack again with the paintbrush to brush away loose debris.

Spread bonding adhesive into the interior of a concrete or cement crack. Use the small paintbrush to apply the bonding adhesive in a thin, even layer and let the adhesive dry for the time that the manufacturer recommends on the product packaging.

Dip a putty knife into an appropriate leveling compound, such as drywall mud for drywall, wood filler for wood and concrete patch for concrete or wood surfaces, and get about an inch of the product on the tip of the knife. Start at one end of the crack and spread the compound over the crack surface until the crack no longer shows through the compound, and then continue along the crack in the other direction once it turns at a right angle.

Get more leveler on the putty knife when you use up the initial compound. Continue down the crack until you have concealed the entire crack beneath the leveling compound. Leave the compound to dry for at least two hours.

Sand down the leveler around the edges of the crack until it feels level with the surrounding wall. Be careful when sanding not to sand too much over the actual crack or you may uncover the crack and have to begin again.