Why This Distinction Matters So Much
Understanding whether a crack is active or dormant changes everything about how you respond.
Dormant Cracks Are History
A dormant crack formed at some point in the past and has since stabilized. The movement that caused it has stopped. Maybe it was curing shrinkage in 1978. Maybe it was early settlement in the first few years. Maybe it was a one-time event. Whatever happened, it's over.
My cracks are dormant. They formed when my house was new. They've been sitting there unchanged for 45 years. They're not hurting anything. They're just... there.
Active Cracks Are Problems
An active crack is still moving. The forces that created it haven't stopped. This could be ongoing settlement, continuing soil pressure, seasonal movement, or progressive failure.
Gary's horizontal crack was active. The soil pressure behind his wall was ongoing. The crack was getting wider every year. That's why he needed wall anchors. The problem hadn't stopped on its own.
Repairs Work Differently
You can seal a dormant crack with confidence. The repair will last because nothing is trying to pull it apart again.
Seal an active crack and the repair will fail. The movement continues, breaks through your patch, and you're back where you started. For active cracks, you have to address the underlying cause, not just the symptom.
How I Know My Cracks Are Dormant
Five years of evidence tells me my cracks have stopped moving.
The Pencil Marks
I marked the end of each crack with a pencil line and a date. If the crack extends past my mark, it's growing. If my marks are still at the ends after five years, it's not.
Every single mark is still at the end of its crack. No growth whatsoever.
The Width Measurements
I measure my widest crack at the same spot each year. It was 1/8 inch five years ago. It's 1/8 inch today. Exactly the same.
If the forces causing the crack were ongoing, it would be wider. It's not. The forces stopped.
The Paint Evidence
Some of my cracks have old paint in them. Clearly been there through at least two painting cycles. Previous owners didn't bother filling them because they weren't causing problems.
Cracks that were stable enough for previous owners to ignore are almost certainly still stable.
The Weathered Appearance
Fresh cracks have clean, sharp edges. Old cracks develop staining, mineral deposits, and a weathered look. My cracks look old because they are old.
Active cracks often look fresher. The edges get cleaned by the movement. The surfaces don't accumulate debris because they're not sitting still long enough.
Signs of Active Cracks
Here's what would make me worried that a crack was still moving.
Fresh Appearance
Clean edges. Clean concrete surfaces. No accumulated dust or debris. A crack that looks new probably is new. And a new crack in an old house means something caused it recently.
Concrete Dust
Fresh concrete dust or small fragments near a crack indicate recent movement. The cracking process generates debris. If there's debris that wasn't there before, something moved.
Failed Repairs
If a previous repair has cracked or separated, the movement is ongoing. A crack that breaks through a patch proves the forces haven't stopped.
I sealed one of my cracks three years ago. The seal is still perfect. That's another confirmation that the crack is dormant.
Measured Growth
This is the definitive test. If measurements show the crack is wider or longer than before, it's active. No ambiguity.
This is why marking and measuring matters. It gives you objective evidence instead of subjective impression.
Seasonal Changes
Some cracks open and close with temperature or moisture. They're not getting progressively worse, but they're not fully dormant either. My friend Dave in Texas has cracks like this. They widen in dry summers and close in wet springs.
These cyclically active cracks are a special category. They need flexible repair methods that can move with them.
How to Test for Activity
Simple methods that give definitive answers.
The Pencil Mark Method
Mark the ends of the crack with pencil lines and dates. Check back in six months. If the crack has extended past your marks, it's active. If not, evidence points to dormant.
This is what I've been doing for five years. It works.
Width Measurements
Measure the width at the widest point. Record the measurement and the location. Check back in six months to a year. Any increase proves activity.
A crack gauge costs $15 and removes the guesswork from this measurement.
Witness Marks
Apply a strip of plaster, drywall compound, or even toothpaste across the crack. If it cracks, movement has occurred. Simple yes-no indicator.
I've never used this method because my pencil marks work fine, but it's a quick test if you want a fast answer.
Full Annual Cycle
Monitor through all four seasons if possible. Some cracks respond to seasonal temperature or moisture changes. A year of observation captures any cyclical movement.
My five years of data covers every season multiple times. If my cracks moved seasonally, I'd know by now.
What This Means for Repairs
Activity level determines repair approach.
Repairing Dormant Cracks
Dormant cracks can be sealed with standard methods. Epoxy injection bonds the crack permanently. The repair will last because nothing is trying to break it.
I sealed my leaking dormant crack with a polyurethane injection kit. Three years later, still watertight. Success.
Repairing Active Cracks
Sealing an active crack is temporary at best. The movement either breaks the seal or opens a new crack nearby. You need to address why it's moving, not just seal where it's cracked.
Gary's active crack needed wall anchors to address the pressure, not just injection to seal the crack.
Cyclically Active Cracks
For cracks that open and close seasonally, flexible sealants work better than rigid ones. The sealant moves with the crack instead of fighting it.
Polyurethane is more flexible than epoxy. Good choice for cracks that aren't fully dormant but aren't progressively worsening either.
Why I Still Monitor
Even though my cracks have been dormant for five years, I still check them annually.
Conditions Can Change
A dormant crack could become active if conditions change. New drainage problems, tree root activity, unusual weather patterns. The crack that's been stable for decades could start moving if something new stresses the foundation.
My annual check takes 15 minutes. Cheap insurance against missing something.
New Cracks Could Appear
I'm not just checking existing cracks. I'm also looking for new ones. A new crack in a 45-year-old foundation would mean something has changed. Worth catching early.
Peace of Mind
Five years of stable measurements gives me confidence. Each year that nothing changes reinforces that my cracks are truly dormant. The data is reassuring.