Some Cracking Is Normal — Some Isn't
It's important to separate harmless hairline cracks from structural problems. As concrete cures it shrinks slightly, and tiny shrinkage cracks are normal. The goal of good concrete work isn't to eliminate every crack — it's to control where cracks happen and prevent the structural cracking that ruins a slab.
The Main Causes of Cracking
Shrinkage: concrete loses volume as it cures; without control joints, that tension can crack the surface randomly.
Poor base prep: an under-compacted or uneven base lets the slab settle and crack — the single most common avoidable cause.
Too much water in the mix: over-wet concrete is weaker and shrinks more, increasing cracking.
Freeze-thaw and de-icing salts: water that gets into concrete expands when it freezes, and salts accelerate surface damage.
Heavy loads on thin slabs: a slab too thin or under-reinforced for its use will crack under the weight it carries.
How the Right Installation Prevents It
Most cracking is preventable with fundamentals: compacting the base properly, using the correct slab thickness and reinforcement, keeping the water-to-cement ratio in check, placing control joints at the right spacing and depth, and curing correctly. Control joints are intentional weak lines that get the concrete to crack in straight, hidden places instead of randomly across the surface.
These steps cost a little more in labor and attention — and they're exactly what separate a slab that lasts decades from one that fails early.
What to Do About Existing Cracks
Small surface cracks can often be sealed to keep water out. Wide, offset, or growing cracks — especially with settling — may signal a base or structural issue that's better addressed by replacement. If you're seeing those signs in a foundation, read our guide on signs you need foundation repair.
Our foundations & slabs page explains how we prep and reinforce to prevent these problems from the start.