Learn what to use when sealing concrete expansion joints to protect against cracks, weeds, and sinking slabs.
Your concrete is constantly on the move, expanding, contracting, and shifting with the seasons. Expansion joints let your slabs flex without fighting against each other, but they must be filled to protect the slab.
TL;DR
Expansion joints let concrete move without cracking, but if left open, they invite water, weeds, and serious damage. Sealing these joints with the right flexible concrete caulk protects your concrete from erosion, heaving, and costly repairs.
In This Article
What Are Expansion Joints?
Expansion joints are intentional gaps between slabs that allow concrete to shift with changes in temperature and moisture. These fluctuations cause the slabs to move due to the concrete and the soil underneath expanding and contracting.
Having a gap to allow for movement without stress on the concrete slabs reduces the likelihood of cracking.
Why Sealing Expansion Joints Matters
Open joints might seem harmless, but they act like runways for water, weeds, and erosion.
Here’s what can go wrong:
- Settling: Water runs through the joint and washes away soil underneath, causing slabs to sink and form trip hazards.
- Heaving: Moisture freezes under the slab and pushes concrete up unevenly.
- Weed growth: Seeds land, sprout, and can crack the concrete further. They also look bad and are hard to remove.
- Cracking from freeze-thaw cycles: Water absorbed by the porous concrete expands when frozen, cracks the concrete, then repeats the damage each winter.
Concrete Gap and Crack Repair
Protect your concrete from settling and worsening cracks with professional concrete crack repair services.
Best Materials to Fill Expansion Joints
The best material to fill expansion joints is flexible, waterproof, and durable self-leveling or non-sag concrete caulk.
Flexible concrete caulk protects against water and weeds and allows the concrete to move as it expands and contracts.
Self-Leveling Caulk
Self-leveling concrete caulk has a thin and fluid consistency, enabling it to smoothly and uniformly fill gaps in joints.
- Flows easily into gaps and smooths itself out
- Must first fill gaps or spaces where the caulk can escape to prevent leaks
Pro Tip: It’s best to avoid self-leveling caulk for joints over 1 inch wide, because the caulk may drop too low after curing and collapse when driven over.
Non-Sag Caulk
Compared to self-leveling caulk, non-sag caulk has a thicker consistency that makes it easier to control.
- Thicker, doesn’t run or drip
- Ideal for wider joints
- Needs to be tooled (smoothed) manually for a clean look
Pro Tip: In some cases, pros use both. Non-sag caulk first to dam leaks, and self-leveling caulk to get a smooth finish.
What to Avoid When Filling Expansion Joints
Wood
Using wood to fill concrete expansion joints was originally thought to be a good idea because wood also expands and contracts with weather fluctuations, but it:
- Doesn’t seal against water intrusion
- Eventually rots or separates
Grout or Mortar
Grout and mortars do not expand and contract with temperature changes, which prevents them from being a long-term solution:
- Too rigid
- Crack under slab movement
- Short-term solution at best
Fill Your Concrete Expansion Joints
If it’s been a few years, or you’re noticing weeds, cracks, or settling slabs, your joints might already be letting trouble in. Caulking them now protects your concrete (and your wallet) long-term.
Request your FREE onsite estimate today and let A-1 help keep your concrete protected.
Still Deciding?
- DIY Guide to Caulking Concrete Cracks and Joints
- How Much Does Concrete Caulking Cost? Concrete Crack Repair Pricing
- 5 Reasons To Repair Concrete Cracks
Frequently Asked Questions
How long does concrete caulking last?
Concrete caulking can last months to years, depending on factors like location, size of opening, and movement in the joint. Proper prep and installation will help it last as long as possible.
Will sealing stop cracks from forming?
Sealing the concrete’s surface helps prevent concrete cracks due to water and freeze-thaw damage, and caulking gaps and cracks can help prevent cracking due to erosion and settling.
How long after concrete caulking until I can use my concrete again?
Wait 24 hours before walking or driving over concrete caulk to give the caulk time to fully set.
Concrete Gap and Crack Repair
Protect your concrete from settling and worsening cracks with professional concrete crack repair services.
