Caulking questions show up one at a time. Weeds in the driveway joints in June, a gap at the stoop in September, a bead that peeled loose over the winter in March. Most of the answers out there were written for places without a Wisconsin winter.
These are the questions we hear most, grouped by topic and answered for concrete in northeast Wisconsin. Short on time? Start with the cheat sheet.
The Cheat Sheet
| Your situation | Caulk it? | What comes first |
|---|---|---|
| Joint open, slabs level, collecting sand or weeds | Yes | Dig it out, let it dry, backer rod if it's deep |
| Old caulk split, peeling, or hard as plastic | Yes | Cut out all the old material |
| Hairline crack, both sides flush | Usually not | Mark it, photograph it, check it next spring |
| Crack or joint where one side sits lower | Not yet | Lift the low slab, then seal |
| Slab at the house tips toward the foundation | Not yet | Lift it so it pitches away, then seal |
| Old wood or fiberboard strip, soft or missing | Yes | Pull what's left of the strip |
| Joint edges crumbling or broken off | Not yet | Edge repair by a concrete contractor |
| Concrete poured this year | Not yet | Let it fully cure |
| Cracks inside a garage you plan to coat | Not with flexible caulk | Rigid filler during coating prep |
| Weep holes at the bottom of brick | Never | Leave them open |
Why Caulk at All
What actually happens if I leave my driveway joints open?
Every open joint is a funnel to the gravel and soil under two slabs at once. Rain and snowmelt run in, carry fine soil away, and leave hollow spots that let slab edges drop. In winter, water in the joint and the base below freezes and expands about 9 percent, prying at the edges. Meanwhile sand and grit pack the joint so it can't close when the concrete swells on a hot day.
Will caulk stop my slab from sinking?
It can help keep a slab that's still in position from sinking, by shutting off the water that washes soil out from under it. It can't bring back a slab that already dropped, and the void under that slab is still there after you seal over it. If a slab has sunk, lift it first, then seal. Handle the bigger water sources too: a downspout dumping beside a slab will undermine it through the soil at its edge, sealed joints or not.
Is it worth caulking an old driveway I might replace in a few years?
Usually, yes, as long as the slabs are in decent shape and reasonably level. Caulking costs a small fraction of replacement, and it slows the washouts and edge damage that could make "a few years" arrive sooner. If the driveway is already broken into pieces, heaved, or crumbling at the joints, put that money toward the replacement instead. Our guide to repairing, resurfacing, or replacing a driveway can help you decide.
Which Joints and Cracks
If I can only do a few joints this year, which ones come first?
Start where water collects or gets concentrated. In order: the joint where any slab meets the house, the joint between the garage floor and the apron, any joint a downspout or sump line drains across, and joints at the low end of a sloped driveway or walk. Joints in the middle of a patio that drains well can wait a season.
Do hairline cracks need caulk?
Most don't. A thin crack with both sides flush is usually shrinkage, and sealant smeared over the top of it tends to peel right off. Pencil a mark at each end, take a dated photo, and look again after the spring thaw. If a credit card slides in, the crack is open enough to hold sealant and worth closing up; if one side has started to drop, read the next question.
Can I caulk a crack where one side sits higher than the other?
You can, but it won't fix what's wrong. The low side dropped because the soil under it compressed or washed out, so there's usually a hollow underneath, and the trip edge stays right where it was. A fresh bead on an offset also sits exposed to every shovel and snowblower that catches the lip. Lift the low slab level first, then seal the crack.
Are there any gaps I should leave open?
Yes. Leave the weep holes in the bottom row of brick veneer open, since they let water out of the wall, and don't push sealant up behind siding or trim. Skip flexible caulk inside a garage you plan to coat, because coatings don't bond to it. And don't caulk a joint whose edges are crumbling, because sealant needs solid concrete to grip.
Materials
Is the caulk from the hardware store good enough?
It can be, if you buy the right kind. Look for a polyurethane or hybrid polymer sealant labeled for concrete joints and rated to ASTM C920, Class 25 or higher, with "T" for traffic if anything walks or drives on it. Grab self-leveling for flat joints and non-sag for sloped or vertical ones. Leave acrylic latex, painter's caulk, and tub-and-tile silicone on the shelf. Our concrete crack caulk guide decodes the rest of the label.
Why not just fill the joints with mortar or concrete patch?
Because joints exist so concrete can move, and mortar can't. Slabs grow on a July afternoon and shrink on a January night, and a rigid plug either cracks loose and lets water back in or holds on and chips the slab edge. Flexible sealant stretches and squeezes with the joint instead. Rigid filler does have one job on our list: filling stable cracks in a garage floor before it gets coated.
Can I caulk over old caulk?
No. New sealant bonds to whatever is under it, so if the old bead is failing, the new one fails right along with it. Sealant makers call for removing all the old material from previously sealed joints, which usually means a utility knife, a stiff wire brush, and some patience. Old silicone is the worst offender, since its residue can keep new sealant from bonding.
Do I really need backer rod?
On any joint deep enough to take it, yes. The closed-cell foam rope sets the sealant depth, generally about half the joint width and between 1/4" and 1/2", so the bead stays thin enough to stretch. It also keeps the sealant off the bottom of the joint, so it grips only the two sides and can flex instead of tearing. And it fills space that would otherwise swallow expensive sealant.
How many tubes will my driveway take?
Measure the total length and the width of your joints, then use the table below, which is the volume math for a bead about half as deep as the joint is wide. A standard 10.1-ounce cartridge holds about 18 cubic inches of sealant. For example, a two-car driveway 20 feet wide and 40 feet long, with a joint down the middle (40 feet), crosswise joints every 10 feet (3 × 20 = 60 feet), and the joint at the garage (20 feet), has about 120 feet of joint. At 1/2" wide, that's about 10 cartridges, so buy 11 or 12.
| Joint width | Bead depth | Feet per 10.1 oz cartridge | Feet per 20 oz sausage pack |
|---|---|---|---|
| 1/4" | 1/4" | About 24 | About 48 |
| 1/2" | 1/4" | About 12 | About 24 |
| 3/4" | 3/8" | About 5 | About 10 |
| 1" | 1/2" | About 3 | About 6 |
These are best-case numbers. Real joints wander in width, so add 10 to 15 percent, and buy backer rod by the same total footage.
Timing and Weather
When's the best time of year to caulk concrete in Wisconsin?
Late summer through early fall. Most joint sealants want at least 40°F and a dry, frost-free joint, and Green Bay's normal overnight low is about 35°F in April and 46°F in May before sliding back to about 39.5°F in October. September brings dry concrete, mild days, and joints near the middle of their movement range, which is what sealant makers prefer. Spring works on dry stretches, but meltwater and rain keep joints damp longer than they look.
How dry does the joint have to be?
Bone dry, all the way down to the backer rod. After a soaking rain, a joint can stay damp for a day or more, and morning dew wets it again even in clear weather, so afternoons after a dry spell are best. Don't pressure-wash the day before, either. A quick check: press a paper towel into the bottom of the joint, and if it comes up damp or picks up dark, wet grit, wait.
How long should I wait to caulk a brand-new driveway?
Until the concrete is fully cured, which is exactly what the sealant data sheets we checked say, often without giving a number. About a month is a safe rule, and it lines up with the 14 to 28 day cure that concrete sealer labels commonly ask for. If the slab went in late in the fall, that may push caulking to next spring, which is fine. One more new-concrete rule while you wait: no deicing salt on it the first winter.
Lifting Plus Caulking
Why lift before caulking instead of the other way around?
Lifting changes the shape of the joints. As a slab comes up, the gap beside it can open, close, or shift, and sealant laid beforehand would tear or have to be cut out and redone. So the order is lift, patch the 5/8" injection holes, then seal, often in the same visit. You can drive on a lifted slab the same day, but fresh caulk still needs the time on its label, so you may have to park around the beads for a bit.
Can you lift a slab that already has caulk in its joints?
Usually, yes. Old caulk, packed dirt, or a wedged wood strip can lock a slab to its neighbor, so we clean out any joint that would bind before we lift, and the slab rises freely. Once it's in position, those joints get fresh backer rod and sealant. Caulk that's in good shape on joints that won't move during the lift can often stay where it is.
Does sealing the joints protect the foam under a lifted slab?
The foam doesn't need it: cured lifting foam is waterproof and won't wash out. What sealing protects is the soil beside it, which water running down an open joint can still soften and carry off. Sealed joints plus downspouts pointed away give a lifted slab its best shot at staying put.
Aftercare and Lifespan
How long does joint caulk last up here?
A good flexible sealant set over backer rod in a clean, dry joint commonly lasts several years and often close to ten. Full sun, lots of joint movement, and plow scraping wear it out sooner. Walk your joints each spring after the snow is gone and look for splits, edges pulling away, or sealant that has turned hard and cracked.
Why did my caulk pull away after one winter?
Usually one of five things: a damp or dusty joint, no backer rod (so the bead stuck to the bottom and tore), a bead too thick to stretch, a latex or general-purpose caulk, or installation on a hot day when the joint was squeezed to its narrowest. Concrete shrinks in the cold, so joints open wider in January than they were in July, and a Class 25 sealant handles about 25 percent movement either way. A 1/2" joint sealed with it can live anywhere from about 3/8" to 5/8" wide, and a joint that swings wider than that can tear the bead. If the slab itself shifted, no sealant keeps up; that one needs lifting.
Will my snowblower or plow tear it out?
Not if it went in right. The finished bead should sit slightly below the slab surface, which sealant makers often put at about 1/8" to 1/4" depending on the joint, so blades ride over it. Beads left sitting proud of the surface are the ones that get peeled out on the first pass. On your own snowblower, set the skid shoes so the scraper bar skims the concrete instead of grinding into it.
If I'm having my concrete sealed, do the joints still need caulk?
Yes, because they're different jobs. A penetrating sealer soaks into the surface and helps the concrete shed water and salt, but it can't bridge a gap, so an open joint stays open. Caulk goes in first and cures, and the sealer goes on after, since caulk bonds best to concrete with no water repellent on it. Our clean and seal guide walks through the full order.
DIY vs. Us
Can I do this myself?
If the slabs are level, the joint edges are solid, and you'll take the prep seriously, yes. A caulk gun, a few tubes, backer rod, a utility knife, a wire brush, and a shop vac handle most walks, stoops, and patios in an afternoon. Most failures come from rushed prep, not bad sealant. Pick a dry, mild day, get every joint clean and dry, and keep the bead a little below the surface.
When does it make sense to hire it out?
When something has to happen before the caulk: a slab that dropped at a joint, a stoop or patio tipping toward the house, or a driveway full of rotted wood strips to pull. Big footage is another reason. We lift sunken slabs with polyurethane foam through dime-sized holes and seal the joints right after. See how a sealing day runs in our concrete caulking process, and if your slabs are fine and you're handy, we'll tell you to do it yourself.
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Rise & Shine Concrete provides foam concrete lifting, concrete cleaning and sealing, joint and crack caulking, and garage floor coatings for homeowners in Green Bay, De Pere, Suamico, Howard, Ashwaubenon, and across northeast Wisconsin.