Joint and crack sealing fills the gaps between and through concrete slabs with a flexible sealant, so rain and snowmelt can't run underneath and wash the base out. It's the single best way to keep lifted concrete level, and it's usually done right after lifting while we're already on site.
By Rob Diederich, owner · Updated
Priced by
Linear foot
Best timing
Right after lifting
Cure
Hours
Re-check
Every few years
Why sealing matters
Open joints are where most sunken concrete starts. Water runs in, carries fine soil away, and freezes in the gap every winter. Sealing closes that path.
Water washout
Roof and downspout water runs into open joints and carries fine soil out from under the slab. The slab drops into the hollow.
Fix: We seal the joints, and point out downspouts that need extending.
Freeze-thaw
Clay-heavy Green Bay soil holds water. Every winter it freezes, swells and thaws softer, loosening the base a little more each year.
Fix: Sealed joints keep water out of the base, which is what freezes.
Settling backfill
The soil pushed back against a new foundation is rarely compacted well. Anything sitting on it settles for years after the house is built.
Fix: Foam fills the voids and stiffens the zone under the slab without adding weight.
Thin or loose base
Some slabs were poured on a thin or poorly compacted base. Gaps under the slab let it settle at joints and corners.
Fix: Foam fills the gaps and supports the slab across its whole footprint.
Three of those four start with water getting under the slab. That's why every lift we do ends with sealed joints, and why sealing on its own is worth doing before anything sinks.
What we do
1Clean out the jointDirt, weeds and old failed sealant come out, so the new sealant bonds to clean concrete.
2Backer rod where neededWide joints get a foam backer rod so the sealant is the right depth to stretch and compress.
3Flexible sealantA sealant made to move with the slabs through freeze-thaw, tooled smooth.
Sealing vs. sealer
Joint sealing fills gaps. A concrete sealer is a clear coat on the surface that slows down salt and water damage. They do different jobs; this page is about the joints.
Questions
Common questions
How long does joint sealant last?
Several years in most cases, depending on how much the slabs move and how much sun the joints get. We recommend a quick look every few years and touching up any section that has pulled away.
Can you seal cracks as well as joints?
Yes. Cracks get cleaned out and filled with the same flexible sealant, so water can't get under the slab through them.
Do I need sealing if I'm getting my concrete lifted?
We recommend it. Lifting fixes the result of water getting under the slab; sealing stops the cause. Together they keep the concrete level far longer.
