Is That Crack In My Foundation Just Cosmetic?

Picture this: you’re grabbing something in your basement when you notice something… a crack. Your stomach drops a little. Is this just normal settling, or is your foundation trying to tell you something serious?

Key Point: Not all cracks are created equal. Hairline cracks are usually cosmetic, but a stair-step pattern, a horizontal fissure, or anything wider than 1/4 inch likely signals a bigger issue that needs professional eyes. In short, hairline cracks = probably fine, but big or patterned cracks = get them checked.

What Makes a Crack “Just Cosmetic”?

Here's the thing about older homes in the Boston area: they move. Especially if you're dealing with historic brick or stone foundations that have been around since the 1800s. Some minor cracking is normal and expected. In Massachusetts, roughly 30% of homes were built before 1940, so having an older foundation is very common. Cosmetic cracks are typically:

• Hairline thin: Usually less than ~1/16 to 1/8 inch wide (a couple of millimeters). These tiny cracks often result from normal curing or settling and generally don’t threaten the structure. They’re kind of like wrinkles… not ideal, but not dangerous.

• Vertical or slight diagonal: Cracks running up-and-down (or at a gentle angle) are common from settling. If they’re uniform width and not very large, they’re usually less concerning than horizontal cracks.

• Not growing or changing: A stable crack that isn’t getting longer or wider over time is more likely to be cosmetic. (It’s still smart to monitor it, which we’ll get to in a bit.)

• Surface-level only: If the crack doesn’t go through the full depth of a wall or foundation, it’s more likely just a surface blemish.

However, even "cosmetic" cracks in historic brick can let water in. And in Massachusetts, with our frequent freeze-thaw cycles, water is enemy number one. Water seeping into a small crack can freeze in winter, expanding by around 9% in volume when it turns to ice, which gradually pries the crack open wider. Over successive freeze-thaw cycles, a once-hairline crack can widen and spread. This means even a harmless-looking crack could invite moisture problems (like seepage or mold) and get worse over time if not kept dry.

When Does Cosmetic Become Structural?

The shift from "eh, no big deal" to "we need to call someone" can happen faster than you'd think. Here are some red flags that a crack may be more than just cosmetic:

• Stair-step patterns in brick mortar joints: Zigzag cracking is a classic sign of foundation movement or settlement. In brick or block walls, cracks following the mortar lines in a step-like pattern act as red flags indicating a potentially significant foundation problem.

• Horizontal cracks (especially in poured concrete): Horizontal fissures are typically more serious than vertical ones. They often indicate pressure from the surrounding soil or water (hydrostatic pressure) pushing against the foundation. A horizontal crack in a basement wall can mean the wall is starting to bow inward under outside pressure – a condition that, if left unchecked, can even lead to wall failure.

• Cracks wider than 1/4 inch: Width matters. A crack you can fit a quarter into is beyond the “hairline” category. The National Association of Home Builders (NAHB) advises that any foundation wall crack over 1/4-inch wide should be repaired. Most foundation experts actually recommend paying attention once a crack exceeds about 1/8-inch, before it gets to that point. In practical terms, if a crack is roughly the width of a pencil or more, it's time for a professional evaluation.

• Cracks that keep growing: If you’ve marked or measured a crack and noticed it expanding, that’s a strong indicator of an ongoing structural issue. (Some experts suggest outlining the crack with a pencil and recording its length and width, then checking again every few months. If it’s getting longer or wider, something is shifting that shouldn’t be.)

• Any crack paired with other symptoms: This is the one-many punch. Doors or windows sticking suddenly? Uneven floors or tilting floors? Gaps around window frames or between walls and ceilings/baseboards? These are all warning signs that accompany foundation movement. For example, if a previously smooth-closing door in your home now jams or a floor has a noticeable slant, it could mean part of the foundation has moved enough to distort the frame of the house.

We’ve seen homeowners ignore a "small" crack for two years, only to find out their foundation wall was bowing inward by the time they finally acted. Not fun, and certainly not cheap. The truth is, foundation cracks don’t fix themselves and usually worsen over time if the underlying issue isn’t addressed. What starts as a minor fissure can expand into a major problem (and a much more expensive repair) down the road In one extreme case, a horizontal crack coupled with stair-step corner cracks led to a noticeable inward bulge in the wall – a problem that requires significant structural bracing to stabilize. The lesson? Pay attention to the warning signs before a small crack becomes a big headache.

What Should You Do When You Find a Crack in Your Foundation?

First: don’t panic. Seriously, most cracks aren’t an immediate danger. Houses (especially old ones) do a fair bit of moving and adjusting over decades. Take a deep breath.

Second: document it. Take clear photos with something for scale (a coin or ruler works great). Mark the ends of the crack with a pencil or piece of tape. Note the date and measurements (if you can measure the width, even better). This gives you a baseline. Check back in a month or two and see if the crack has gotten longer or wider. Keeping a simple log (even just notes in your phone) of crack changes is incredibly helpful. If you notice growth, that’s valuable information for a professional later. And if the crack doesn’t change over time, that’s reassuring data as well.

Third: if you're seeing any of those red flags we talked about (stair-steps, horizontal crack, >1/4 inch, growing, etc.), or if you just want peace of mind, call someone who knows what they’re looking at. A proper evaluation by a foundation expert or structural engineer beats guessing every time. Foundation professionals can perform an inspection to determine the cause of the crack and the best course of action. They might use tools like laser levels to check for wall bowing, or moisture meters to detect water intrusion. After an expert evaluation, you’ll know whether it truly is “just cosmetic” or something that needs repair.

For historic homes especially, you want someone who understands how old brick and mortar behave. Slapping modern epoxy or cement onto a century-old brick wall might seal a leak for a bit, but it could create long-term issues (like sealing in moisture or causing more brick damage). The right historic restoration professional will suggest solutions that suit the age and construction of your home; whether that’s using a lime-based mortar for a 200-year-old brick, installing proper drainage to relieve soil pressure, or simply monitoring the crack. Remember, applying the wrong fix can be as bad as doing nothing, so getting an expert opinion is key.

Finally, don’t delay if the crack is serious. If there is one message to take away, it’s that foundation problems only get more expensive the longer you wait. It’s far better (and usually cheaper) to address a minor structural crack now than an extensive foundation failure later.

About JMS Masonry

JMS Masonry was founded on a simple idea: historic buildings deserve craftspeople who actually care about preserving them the right way. Based in Woburn and serving the greater Boston area, we specialize in traditional masonry techniques that honor the original construction methods of old New England homes.

Whether it's repointing 200-year-old brick, foundation stabilization and repair, or full historic restoration work, we're the team that shows up with the right skills and the right materials for the job. 

Ready to get that crack looked at? Contact JMS Masonry for an honest assessment. We'll tell you what you're dealing with, and what you're not. No scare tactics, no hard sell. Just straight talk from folks who have been doing this long enough to know the difference between normal aging and actual trouble. Your peace of mind (and your home’s stability) are worth it.