Step 1
Place the stepladder directly under the ceiling crack and mount the ladder. Clean the surface of the crack with a soft-bristled brush to remove crumbling drywall or plaster bits. Wipe the cracked surface with a damp cloth to remove dirt and residual debris. Let the surface of the ceiling around the crack dry thoroughly.
Step 2
Insert a tube of silicone caulk into the caulking gun, push the plunger to the base of the tube and release the spring. Use a utility knife to cut off the tip of the tube at a 45-degree angle. Form a hole in the tube that matches the width of the crack you want to seal.
Step 3
Insert a long nail into the hole to break the seal. Press the trigger so it pushes the caulk out of the tip of the tube. Push the release latch located at the back of the caulking gun to stop the flow of silicone caulk.
Step 4
Position the tip of the gun diagonally over a corner of the ceiling crack. Press the trigger to release the silicone caulk into the crack. Apply steady pressure on the trigger and move your hand slowly along the crack, from one end to the other, so you lay a smooth bead of caulk into the visible gap. Press the release latch when you reach the end of the crack.
Step 5
Wet your thumb and press it lightly over the silicone caulk line, moving along the crack to smooth out the surface. Let the caulk set for 24 hours. Wipe away accidental caulk from around the edges of the crack with a wet rag.