Block Weeds From Growing Along Driveway Expansion Joints

We’ve all seen them. Weeds. Along your concrete driveway expansion joints. Many, if not most, people will just remove the weeds only for them to grow back as soon as it rains. So, why do weeds grow along these lines? Apparently just a little bit of dirt that makes its way into these gaps is enough to cause weeds to grow. I’ve had enough of these weeds growing every year so here’s my attempt to resolve this annoyance once and for all.

Fill Gaps

Now, my driveway has gaps that are small (1/4″), medium (1/2″) and wide (3/4″ – 1″) in width and the depths range from 1/4″ to maybe 3″ deep. The small and shallow gaps are usually not a problem.

At first, I thought about filling some small gaps with Sakrete Concrete Crack Filler since the driveway is made of concrete.

Concrete Crack Filler

I tried this on a small gap and product was very easy to apply and it settles nicely producing a nice bead.

However, it turns out you shouldn’t do that because apparently those gaps – called expansion joints or control joints – are by design so filling these gaps with concrete defeats their purpose. Concrete Crack Filler is good, however, if you do have a thin, natural crack (not expansion joint) because it hardens just like concrete.

Concrete Filler and Sealant

What you want to use for these gaps is a flexible sealant like caulk but designed for concrete. I found three products that are designed for this.

If your driveway joints are on a slope, which is most likely the case, then make sure not to buy self-leveling sealant.

Foam

Now, for some of the larger gaps, it would be too expensive and wasteful to fill them with sealant. For those, I decided to use a foam gap filler.

This stuff really does expand and is pretty sticky when wet. It’s great for filling large gaps. Of course, you’ll need to trim the foam in order to apply sealant. This can be done with a utility knife, a mini reciprocating saw, or, better yet, an oscillating tool.

I cut away the foam a little bit below the surface of the concrete to allow for a layer of sealant.

Apply Sealant

I first tried the Sikaflex Construction Sealant on a medium-sized gap without any foam filling. Unlike baseboard or window caulk, this sealant is very sticky and is hard to get off your hands. However, when it dries, it’s harder than regular window and trim caulk.

Sikaflex Construction Sealant applied to a control joint

Normally when caulking baseboard, you’d smoothen the bead with your finger and then wipe the caulk with a damp sponge to get smooth, professional results. Well, that trick didn’t work with the concrete sealant, mainly because it was just too sticky. As a result, I just used my finger and as you can see, the bead isn’t perfectly smooth.

Next, I tried the DAP concrete sealant on a joint filled with foam. I just used my finger to smear the sealant level with the adjacent concrete.

However, I really didn’t like how the bead wasn’t smooth. So, I tried spraying some water to moisten the sealant and then try smoothening it out again with my finger. This produced much better results.

Left: smoothened sealant, Right: unsmoothened sealant

From close up, it’s still not perfectly smooth but at a distance, it looks acceptable.

After about 24 hours, I found the Sikaflex sealant to be harder than the DAP sealant. For that reason, I may go back to using Sikaflex but spray some water on it to smoothen it out before letting it cure.

Now, if you don’t like the look of a gray joint, you can color your driveway with Rustoleum Epoxy or Behr Granite Grip and the entire driveway will be the same color.