How to Caulk Concrete

Use foam backer rod and keep the caulk bead thin.

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For long-lasting concrete crack repair, fill wide cracks with foam backer rod before caulking. And use a caulk formulated for concrete.

Tools Required

  • Caulk gun
  • Plastic spoon
  • Putty knife

Materials Required

  • Backer rod
  • Caulk
  • Caulk remover

Project step-by-step (3)

Step 1

Clean the edges


Clean the old caulk from edges of the crack using a chemical cleaner or mineral spirits. If the caulking keeps peeling up from the cracks in your concrete patio, try this professional solution. Use a combination of backer rod (inexpensive at home centers) and caulk. First remove the caulk that’s in the gap. For latex caulk, pour caulk remover (such as Lift Off; about $6 at home centers and hardware stores) over the caulk, let it sit for two hours, then dig out the caulk with a stiff putty knife. For silicone or polyurethane caulk, use mineral spirits.

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Step 2

Continue scraping


If you’re not sure what type of caulk you have, start with the caulk remover. For stubborn sections, give the remover more time to work, then continue scraping. You don’t have to remove every last piece of caulk, especially if it’s at the bottom of the gap, but the top 1 in. of the crack needs to be cleaned off pretty well. Learn more about concrete repair here.

Step 3

Backer rod is the key

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Insert backer rod into the gap, then run a bead of caulk over the top. For a smooth, even bead, tool the caulk with a plastic spoon. Use a backer rod with a diameter that’s 1/8 to 1/4 in. larger than the crack. Push the rod into the gap so the top is about 1/4 in. below the concrete surface. Fill the gap with caulk, them smooth the caulk with a plastic spoon. Be sure to use a caulk that’s formulated for use with concrete (it’ll say so on the label). Next, check out our expert tips for caulking here.

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