Fill big gaps before caulking
1 of 2
Photo 1: Clean the edges
Clean the old caulk from edges of the crack using a chemical cleaner or mineral spirits.
2 of 2
Photo 2: Backer rod is the key
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.
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; Photo 1) 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. 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.
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 (Photo 2). 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).