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Concrete · You can handle this

Expansion joints filled with debris

Clear them and refill with a flexible joint sealant. Joints exist to let the slab move; packed with grit they cannot, and the slab cracks somewhere else instead. You can handle this one yourself. No call needed.

Quick answerJoints in a driveway or walk give the concrete room to expand and contract. When they fill with grit, stones, soil and weeds, the slabs can’t move freely, and the stress cracks the concrete somewhere else. Dig the joints out, clean them, and refill with a flexible joint sealant made for concrete. It’s an afternoon job with basic tools.

Open joints also let water straight into the base under the slab. Sealing them keeps the ground underneath drier, which helps prevent settling and frost heave.

1Why it matters

  • Movement. Concrete grows and shrinks with temperature. Joints take that movement. A joint packed solid can’t.
  • Water. An open joint is a funnel into the base. Wet soil under a slab settles and, in cold climates, heaves.
  • Weeds. Roots in a joint widen it and hold moisture against the edges.
  • Original filler failing. Fiber or foam filler from the original pour breaks down over time and leaves a gap that fills with grit.

2How to clean and reseal a joint

  1. Dig it outUse a screwdriver, a joint raking tool or an old chisel to pull out old filler, soil, stones and weeds.
  2. Clean and dry itBlow or vacuum out the dust and let the joint dry fully. Sealant won’t stick to wet or dusty concrete.
  3. Add backer rod if it’s deepPress foam backer rod into deep joints so the sealant sits at the depth the product directions call for.
  4. Apply the sealantUse a flexible sealant rated for concrete joints. Self-leveling types suit flat driveways; non-sag types suit sloped areas.
  5. Keep traffic offFollow the cure time on the tube before you walk or drive over it.
Tip

Use a flexible sealant, not mortar or rigid patch. A hard fill defeats the purpose of the joint and will crack out.

3When it’s more than a joint problem

Do it yourself

  • Joints packed with grit, soil or weeds
  • Old filler crumbling or missing
  • Slabs either side are level and sound

Look closer first

  • One slab is noticeably lower than the next
  • Cracks are already running across slabs
  • The joint is pushing up or the slabs are tilting

If slabs are uneven, see driveway settling near the garage or tree roots lifting a section before sealing.

4What drives the cost

Sealant, backer rod and a caulk gun are the main costs. Longer driveways with many joints take more material and time. This is one of the jobs we list as something you should not be paying much for.

Concrete cost

5Questions

How often should joints be resealed?

Check them each spring. Reseal when the sealant is cracked, pulled away from the edges, or missing.

Can I use regular caulk?

Use a sealant rated for concrete joints and outdoor use. It needs to stay flexible through heat and cold.

Should I fill the joint flush?

Follow the product directions. Many recommend setting the sealant slightly below the surface so tires and shovels don’t pull it out.

Written by Jaylan Jones. I Like To Exterior Services earns a referral fee when a call connects to a contractor. See our business-model disclosure.