Basics

Why Water Decides How Long a Slab Lasts

Concrete does not really wear out. It gets undermined. Almost every failed slab we are asked to look at has the same story underneath it, and it is a story about drainage.

Updated October 2026 · Burlington Concrete

Ask what makes a driveway last and most answers will be about the concrete: how thick, what mix, how much steel. Those matter. They matter considerably less than where the water goes, and that is worth understanding before you spend money on the wrong half of the problem.

A slab is not attached to anything

Start with a distinction that explains the rest of this page. A building sits on footings taken down below the reach of frost. Wisconsin puts that requirement plainly: footings go below the frost penetration level or at least 48 inches below adjacent grade, whichever is deeper, and that last clause is the one most national writing drops.

Your driveway has none of that. It is a slab on grade. It rests on compacted material, it is jointed so it can move a little without tearing, and nothing anchors it to anything. Which means the thing holding your driveway at the right height is not the concrete. It is the few inches of stone underneath it, and that material is vulnerable to exactly one thing.

What water does to a base

A properly built base is graded stone compacted in layers, and it works because the fine material packs into the spaces between the larger pieces until the whole thing behaves almost like a solid.

Run water through it and those fines are the first thing to move. They are small, they are light, and flowing water carries them away. What is left behind is coarser, less tightly interlocked and occupying slightly less space than it did.

That process is invisible and slow. It goes on for seasons with nothing showing at the surface, and then one spring the slab finds the void that has developed and drops into it. The crack that appears is the last event in a long sequence, not the first.

The freeze-thaw multiplier

Here, that ordinary erosion story picks up a local accelerant. Saturated ground swells as it freezes and drops back as it thaws, and this corner of Wisconsin delivers that cycle over and over through the cold half of the year.

Dry ground does very little of this. Wet ground under a slab lifts it slightly, lets it back down, and does so repeatedly, which loosens the base further and pumps yet more fine material out from under the edges. Water is both the erosion and the jack.

This is why two identical driveways on the same street can be twenty years apart in condition. The difference is almost never the concrete. It is that one of them sheds water and the other collects it.

Where the water actually comes from

• Downspouts. The commonest single culprit, discharging at the edge of a slab and putting the entire roof area into one square foot of ground.
• The fall of the surface itself. A driveway that sends water toward the garage rather than away is delivering it to the worst possible place, repeatedly.
• The ground alongside. A lawn or bed sitting higher than the slab lets water run sideways underneath it rather than off it.
• An edge nobody finished. Where a slab meets soil with no defined edge, water finds that line and follows it down.
• Snow piled on it all winter. A plough heap sitting on one area is a slow continuous soak for months, exactly when the freeze cycles are happening.

What good construction does about it

Falls that are designed rather than inherited. A slab should shed water in a direction somebody chose, and on flat ground achieving that means the excavation is deeper at one end than the other, which costs money and does not show.

A base that drains rather than holds. Graded stone that lets water pass through and away, over ground that has been looked at rather than assumed.

Edges that are defined, so the boundary between concrete and soil is not an open invitation. And downspouts taken somewhere deliberate, which is frequently the cheapest single improvement available on an existing driveway.

The edge, which is where it usually starts

If you want to know where a slab will fail first, look at its perimeter. The middle of a driveway is protected by everything around it. The edge has ground on one side, weather on two and nothing holding it down.

Water running off the surface arrives at that edge concentrated, and if the soil beside it is lower, it cuts a small channel and starts working underneath. Once there is a route under the edge, every rainfall extends it inward, and the corner that eventually breaks away was undermined months before anything looked wrong from the house.

This is why a defined edge earns its place, and why the strip of ground immediately alongside a slab is worth keeping level with it rather than letting it wash out into a trench. It is also why the corner nearest the downspout is so often the first thing anybody notices.

What to do with this before you buy anything

Go and look during heavy rain. Not afterwards. Watching where water actually travels across your own ground for ten minutes tells you more than any amount of inspecting the cracks afterwards, because the cracks only tell you that something failed.

Then, if you are replacing a slab that has already failed this way, make sure the drainage is part of the conversation rather than a separate job for later. Pouring new concrete on the same ground with the same water arriving in the same place buys you the same outcome on a delay.

Where the problem is a drive that falls the wrong way, that specific design case is covered in drainage at the bottom of a sloped drive. Whether your existing slab is worth saving at all is worked through in when a driveway actually needs replacing, and new work is on concrete driveway.