The Science Rick Finally Explained
Rick's been patient with me through a lot of foundation panic. Here's how he explained shrinkage cracks over beers one night.
Concrete Is Mostly Water
"You know concrete starts wet, right?" Rick asked me. Obviously I knew that. But I hadn't thought about where all that water goes.
As concrete cures, the water evaporates. And as it loses water, the concrete shrinks. Not a lot. Maybe 1/16 of an inch per 10 feet. But on a long basement wall? That adds up.
It Can't Shrink Everywhere
Here's the thing. The wall wants to shrink, but it's stuck. The bottom is attached to the footing. The top is attached to your house. The corners are attached to the other walls.
The concrete can't shrink uniformly because it's restrained. So it does the next best thing. It cracks.
Rick drew it on a napkin. A rectangle trying to get smaller but held at the corners. "Where does the shrinkage go?" he asked. "Into cracks. That's the only option."
It Happens Fast
Most shrinkage happens in the first year. The big stuff happens in the first few months. By the time a foundation is 5 years old, shrinkage is basically done.
My house was built in 1978. Those shrinkage cracks have been there since I was a kid. They're not going anywhere.
How to Recognize Shrinkage Cracks
The engineer walked me through my basement and pointed out every crack that was just shrinkage. Turns out I'd been panicking about textbook examples.
They Run Vertical
Most shrinkage cracks go straight up and down. The wall is thin compared to its height, so cracks take the shortest path through. Vertical is shortest.
Horizontal cracks are different. Those usually mean pressure from outside. But vertical? Classic shrinkage.
They Start at Stress Points
The engineer pointed at each of my cracks. "Window corner." "Pipe penetration." "Wall corner." Every single one started at something. A hole, a corner, a penetration.
These features concentrate stress. When the wall shrinks, that's where it cracks. A crack running from a window corner isn't alarming. It's expected.
They're Narrow and Consistent
My shrinkage cracks are all hairline to about 1/8 inch. They're roughly the same width along their whole length. They don't get dramatically wider at one end.
If a crack is way wider at the top than the bottom, something moved. That's not shrinkage. But consistent width? That's concrete doing what concrete does.
They Don't Move
This is the big one. Shrinkage cracks form once and stop. They don't get wider year after year. They don't extend further up the wall.
I've been tracking my cracks for four years. Pencil marks at the ends. Width measurements. Photos. They haven't changed at all. That's how I know they're just shrinkage.
How I Know Mine Aren't Structural
The engineer gave me a simple framework for distinguishing shrinkage from structural cracks.
No Displacement
He ran his hand across each crack. "Both sides level?" he'd ask. Yes, every time. If one side had shifted forward or back, that would indicate actual movement. But just separation? That's shrinkage.
No Pattern of Failure
Structural problems create patterns. Multiple cracks radiating from one area. Wall cracks continuing into ceiling cracks. Floor cracks aligned with wall cracks. A whole-house story of movement.
My cracks are isolated incidents. This one from this window corner. That one from that pipe penetration. No connection between them. No pattern of failure.
Nothing Upstairs Correlates
The engineer asked if any doors upstairs stick. Any drywall cracks above the basement cracks? Any floors sloping toward where the cracks are?
Nope. Nothing. The rest of the house is fine. Just some cracks in the basement concrete that have been there since Carter was president.
Should I Fix Them?
The engineer's answer surprised me. "Why would you?"
They're Not Doing Anything
Shrinkage cracks don't weaken your foundation. The wall is still doing its job. The cracks are just where the concrete gave a little during curing. Filling them doesn't make anything stronger.
Unless Water's Coming Through
If a crack is leaking, seal it. Not because the crack is structural, but because water in your basement is always bad. I have one crack that showed some efflorescence, that white crusty mineral deposit. That's where water got through at some point.
I sealed that one with an $89 injection kit. Took an afternoon. Problem solved.
Unless You're Finishing the Basement
If you're putting up walls and flooring, seal the cracks first. You don't want moisture problems behind finished walls.
I'm not finishing my basement anytime soon, so I'm leaving most of my cracks alone.
Unless They Bother You
Some people just don't like looking at cracks. That's valid. Fill them for cosmetic reasons if you want. But know that you're doing it for appearance, not for structure.
The $350 Was Worth It
I could have saved that money. Rick would have told me the same thing. But here's why I don't regret it.
Professional Certainty
Rick is smart. But he's not a licensed structural engineer. Having an actual professional tell me everything was fine, in writing, was worth the peace of mind.
I Know What to Watch For
The engineer didn't just say "it's fine." He explained what would make it not fine. What changes would mean I should call him back. What I should be monitoring.
Now I know what I'm looking at. That education was worth $350.
Documentation for Selling
If I ever sell this house, I have a structural engineer's report saying the foundation is sound. That's worth something when nervous buyers start asking questions about cracks.