Every driveway, sidewalk, and patio has joints: the straight lines cut or tooled into the slab, and the gaps where one slab meets another or meets the house. They let concrete crack where it's told to and move without breaking. What shouldn't be there is an open slot a finger wide, full of sand and dandelions.
Most people step over those joints for years, because nothing seems to happen. The damage happens underneath, a season at a time, until a slab sits half an inch low and the snowblower finds it.
Here's what that looks like for one joint over one year, and then over ten. For the how-to, see how to fill concrete expansion joints, and for quick answers, our concrete caulking FAQ.
Meet the Joint
Picture a common one: the first crosswise joint on a two-car driveway, about 10 feet out from the garage door, running 20 feet across. Its sealant is long gone, and it has opened to about 1/2 inch.
The 200 square feet of concrete between the garage door and that joint drains toward the street right across it, and concrete sheds nearly everything that lands on it. Using the same 0.62 gallons per square foot per inch of rain behind our roof water numbers:
- One inch of rain on that 200 square feet sends about 125 gallons across the joint.
- Green Bay's April–October precipitation, 23.3 inches in a normal year by the Wisconsin State Climatology Office's 1991–2020 numbers, sends about 2,900 gallons across it.
- If just one gallon in ten drops in (an illustration, not a measurement), that's roughly 290 gallons poured into the base under one joint in a single warm season. That's before snowmelt, or a downspout aimed at the driveway.
All of it goes into the gravel and soil under two slab edges at once.
A Year in the Life
March and April: the melt pours in
Snowbanks along the driveway shrink every sunny afternoon, and the melt runs across the slab and into the joint.
Underneath, the ground thaws from the top down. Wisconsin's spring road weight limits, which average roughly March 9 to May 9, exist because meltwater gets trapped in that thawed top layer, above soil that's still frozen. The base under your joint is the same: a few inches of saturated, soft material sitting on ice.
Then you drive on it. A slab edge on soupy base can flex just enough under a tire to squeeze water back out of the joint, and fine soil leaves with it. Pavement engineers call this pumping. The clue topside is a thin smear of silt beside the joint after a wet spell.
May and June: the joint fills up
Winter's sand is still in the joint. Then the trees add their share. Around Green Bay, cottonwoods release their fluff in late May or early June, and silver maple seeds ripen by early June and come down right after.
Sand, seeds, and a little organic muck make a seed bed. By late June, grass and dandelions are rooted in the joint, holding moisture against the slab edges and pushing roots into the base.
July and August: heat and downpours
Concrete grows a little when it heats up. On an 81-degree July afternoon (Green Bay's normal high), the slabs expand and the joint narrows. That's the joint doing its job.
But a joint packed with sand and grit can't close. Pavement engineers call that debris incompressibles, and keeping it out is one of the main reasons road agencies seal joints. The slab edges press against packed grit instead of open air, and the pressure chips and spalls the top corners.
Summer is also the wettest stretch of the year. June alone averages 4.1 inches in Green Bay, often in short, heavy storms, and every downpour runs across the driveway and down the joint, washing fine soil out from under the downhill edge. This is when that hollow can grow fastest.
September through November: soaked going into winter
Fall adds another 7.85 inches of rain and early snow in a normal year, and leaves pack in on top of the summer's sand. The base heads into winter about as wet as it gets.
That matters because wet soil is what heaves. Clays and silts are the most frost-susceptible soils, and much of Brown County sits on clay-rich glacial till and old lake clay.
December through February: ice and brine
Water in the joint freezes and expands about 9 percent, prying at the slab edges. Below it, the soaked base freezes too, and a slab edge over wetter soil can get pushed up unevenly, then drop back crooked during a thaw. More on that in frost heave vs. settling.
Then the salt shows up. Brine runs off the slab and sits in the joint against bare concrete, week after week. Calcium and magnesium chloride add another problem: the Federal Highway Administration notes they can react with cement paste to form calcium oxychloride, which expands and damages concrete even above freezing. Joints, where brine collects and lingers, take the brunt. You'll see edges that darken, round over, and flake.
By March, the joint is a little wider at the top, the base under it a little emptier, and the cycle starts again from a worse place.
The Long Game: From Open Joint to Repair Bill
One year rarely sinks a slab. Five or ten can. This timeline is illustrative; how fast it moves depends on your soil, how much water reaches the joint, and what drives over it.
| Joint left open | Underneath | What you notice | Fix at that point |
|---|---|---|---|
| Years 1–2 | The base gets soaked every spring, and fine soil starts migrating | Sand and weeds in the joint; dark, damp edges after rain | Clean it out and caulk it |
| Years 3–5 | A shallow hollow forms under the downhill edge | One slab sits 1/4" to 1/2" low; a silt smear after storms; a puddle that freezes | Lift the low slab, then caulk |
| Years 5–10 | The hollow spreads and the slab loses support along its edge | The slab rocks or sounds hollow; a crack across the panel; chipped, rounded joint edges | Lift if the slab is still in one piece and repair the edges, or replace if it's broken up |
| Any year, at the house | Water runs down the foundation wall instead of away | The slab tips toward the house; a damp basement corner | Lift so it pitches away, caulk, and call a waterproofing pro if water is getting in |
That last row is why the joint along the house matters most. See caulking where concrete meets the house.
What Skipping It Costs
The same joint, three ways:
| Path | What you're paying for | Relative cost | What you end up with |
|---|---|---|---|
| Caulk it now | About two cartridges of sealant for a 20-foot, 1/2" joint, plus backer rod and an afternoon, or a small professional job | $ | A sealed joint, good for several years before resealing |
| Lift and caulk later | Foam lifting for the slab that dropped, then the same caulking | $$ | A level slab with the hollow filled, at a fraction of replacement |
| Replace later | Tear-out and repour. Local cost data from 2022–2024 put Green Bay-area replacement at roughly $8–$15 per square foot, so this example's 200 square feet would run about $1,600–$3,000. | $$$$ | New concrete, plus a new joint that still needs sealing |
The ratio matters more than the exact dollars. Caulking is the cheapest repair here by a wide margin, and the only one you can do before anything has gone wrong.
What Caulking Does, and What It Doesn't
| Caulking does | Caulking doesn't |
|---|---|
| Keep surface water out of the base under the joint | Raise a slab that already sank, or fill the hollow under it |
| Keep sand, grit, and seeds out, so the joint can close in summer heat | Hold a slab up. Sealant is a flexible rubber strip, not structure. |
| Cut how long brine sits against the joint faces | Stop water coming from beside or below the slab: downspouts, poor grading, a high water table |
| Take away the seed bed weeds need | Repair crumbling or spalled edges. It needs solid concrete to grip. |
| Make trouble easy to spot, since a split bead is easier to read than a dirty gap | Last forever. Plan on resealing every several years. |
If water reaches a slab from a downspout or a low spot, sealed joints help but aren't the whole fix. See soil grading around concrete.
Wait, Wisconsin Doesn't Seal Its Highway Joints?
True. In 1990, Wisconsin's Department of Transportation stopped sealing joints on its concrete highways, after its own research found unsealed pavements holding up as well as or better than sealed ones. Pavement engineers still debate it, and most other states kept sealing.
So why seal your driveway? Because a highway is built nothing like one. State highways get thick slabs, engineered base layers (some designed specifically to drain), and steel dowels across many joints to pass loads from slab to slab. Your driveway is a few inches of concrete on whatever base the builder put down, often over loose backfill near the house, with clay underneath, no drainage layer, and maybe a downspout aimed at it.
The highway research shows that a heavily built, well-drained pavement can tolerate open joints. It doesn't show that a thin slab on soggy backfill can.
When Caulking Isn't Worth It
We'd rather tell you this than sell you footage you don't need.
- Hairline cracks with both sides flush. Usually shrinkage, and sealant smeared over a crack too thin to take a bead tends to peel off. Mark the ends, photograph it, and check next spring.
- Joints with crumbling edges. Sealant needs solid concrete on both sides. Breaking edges need repair by a concrete contractor first (not a service we offer), or the slab is near the end of its life.
- Slabs you're replacing within a year or so. Put the money toward the new concrete.
- Slabs that are offset or tipped toward the house. Caulk them where they sit and you lock in the trip edge and the bad slope. Lift first, then seal.
- Concrete poured this season. Let it cure fully, about a month at minimum.
- Narrow saw cuts with level sides out in the open. If it isn't collecting grit, it can wait. Spend your effort on the wide, dirty, or water-fed joints.
Self-Check: Which Joints Are Costing You the Most?
Walk your concrete with a credit card, a straightedge or 2-foot level, and a hammer handle. Score each joint:
| Check | Points |
|---|---|
| A credit card slides in | +1 |
| It holds sand, weeds, or old caulk that's split or pulled loose | +1 |
| A downspout, sump line, or snow pile drains across it or toward it | +2 |
| It's where a slab meets the house or the garage floor | +2 |
| It sits at the low end of a slope, where water collects | +1 |
| You see a silt smear or a fan of sand beside it after rain | +2 |
What the score means:
- 4 or more: Seal it this year, on a dry day around 40°F or warmer.
- 2–3: Seal it when you're doing the others.
- 0–1: Leave it and look again each spring.
Two automatic stops, whatever the score:
- One side sits lower than the other when you lay the straightedge across, or the slab rocks or sounds hollow near the joint. There's likely a hollow underneath. Lift first, then seal.
- The edges are crumbling. Repair first, or plan on replacement.
Where We Come In
We caulk joints and cracks as a job on its own, and often right after a lift. On our jobs, that means a flexible, self-leveling polyurethane joint sealant, with closed-cell backer rod where the joint is deep enough to need it, in joints that are clean, dry, frost-free, and about 40°F or warmer. When a slab has dropped, we lift it first with high-density polyurethane foam through 5/8" holes about the size of a dime, patch the holes, then seal. See how a sealing day runs in our concrete caulking process.
If your slabs are level and you're handy, do it yourself. The prep decides whether it lasts.