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Reading Stucco Cracks: What the Pattern, Width and Location Tell You

Cracking in stucco is common and most of it is not urgent. The useful question is not whether your wall has cracks — almost every stucco wall does eventually — but which kind. Three things narrow it down: the pattern the cracks make, how wide they are, and where on the wall they sit. Here is how to read those three, and where reading them stops being enough.

Why stucco cracks in the first place

Stucco is a rigid cement-based coating applied over a wall that is not rigid. The wall moves — with temperature, with moisture, with the building settling — and the coating has to accommodate that movement without a way of stretching. Some cracking is the predictable result, and it is why control joints and reinforcement exist in the first place.

Calgary adds a specific pressure to that. In a climate where the wall freezes once and stays frozen, water in a crack expands once. Here, chinooks mean the wall thaws and refreezes repeatedly through the winter, so water that has found its way into a crack gets several goes at widening it. That is the mechanism that turns a stable hairline into something else over a few winters, and it is why "is it holding water" is a more useful question than "how wide is it".

One caution before the patterns below. A crack is evidence, not a diagnosis. Each of these patterns has a common explanation and several less common ones, and the same crack can look identical whether the cause is ordinary curing or something behind the wall. The patterns narrow the field; they do not close it.

Five patterns, and what each usually means

Roughly in order from the most frequently seen to the most worth acting on.

Pattern 1

Fine crazing

What it looks like
A shallow network of very fine lines across the surface, like a dried-out lakebed or a cracked glaze. Individually the lines are narrower than a credit card edge.
What it commonly indicates
Usually confined to the outermost finish coat and associated with how the coat cured — a surface that dried faster than it should have, often because it went on in heat or wind. Crazing is the most frequently seen pattern and, on its own, the least likely to indicate anything behind the wall.
What to watch
Whether it is stable. Crazing that has looked the same for years is different from a surface that is opening up further each season.

Pattern 2

Diagonal cracks from window and door corners

What it looks like
A line running away from the corner of an opening at roughly 45 degrees, often on more than one opening on the same elevation.
What it commonly indicates
The corners of openings concentrate stress, and this is where a wall shows it first. Fine, stable versions of this are common on older stucco. Wider ones, or ones that keep growing, are the pattern most worth having looked at, because the same shape can come from movement in the structure rather than from the coating.
What to watch
Width, and whether the same crack appears on several openings. One hairline off one window and a widening crack off every window on a wall are not the same observation.

Pattern 3

Long vertical or horizontal lines

What it looks like
A straight, comparatively long crack that does not radiate from an opening, sometimes tracking a line that repeats at regular intervals up or across the wall.
What it commonly indicates
A straight line running where a joint in the sheathing or a change in the assembly sits behind the finish. It says something about what is behind the stucco rather than about the stucco itself, which is why the fix depends on what that something is.
What to watch
Whether it is holding water — a crack that stays dark long after the rest of the wall has dried is taking water in.

Pattern 4

Stair-step cracking

What it looks like
A crack that steps along in a staircase pattern rather than running straight.
What it commonly indicates
This pattern follows joints in masonry behind or below the finish. Where it appears it is usually taken as a sign of movement rather than of surface curing, and it is the one where an assessment of the structure — not just the coating — is the appropriate response.
What to watch
Any accompanying change in the wall plane: one side sitting proud of the other, or doors and windows in that wall behaving differently than they used to.

Pattern 5

Cracking with staining, powder or hollowness

What it looks like
A crack that is not on its own — dark streaks running from it, white powdery deposits on the surface nearby, or a hollow sound when the area beside it is tapped.
What it commonly indicates
The combination matters more than the crack. Staining suggests water is running somewhere it should not. White deposits indicate water has moved through the assembly and left dissolved salts behind. A hollow sound suggests the coating has lost its bond to what it was applied to. Any of these alongside a crack raises it above cosmetic.
What to watch
All three together, especially low on a wall or under a window, sill or roof line.

What is worth writing down

If you are unsure whether something needs attention now, the most useful step is not to fix it — it is to record it well enough that the answer becomes obvious in a few months. Five observations do most of the work.

  1. 1

    Width, against something you have on you

    Compare the crack to a credit card edge or a fingernail rather than guessing at millimetres. What matters most is not the absolute number but whether the same crack is wider next time you look.

  2. 2

    Whether it is getting longer or wider

    A photo with the date on it, from the same spot, once a season, tells you more than any single inspection can. A stable crack and an active one need different responses, and only time distinguishes them.

  3. 3

    What is directly above it

    A window, a sill, a roof line, a downspout, or a section of failed flashing. Water arrives from above and shows up lower down, so the crack is often not where the problem is.

  4. 4

    Whether it is wet when the wall is dry

    Walk the exterior a day after rain or after a melt. A crack that is still dark when everything around it has dried is taking water in and holding it.

  5. 5

    How close to grade it sits

    The bottom of a wall gets splash-back, banked snow and meltwater running down it, and it is where damage most often starts. That does not make the stucco the cause — grade and drainage are frequently the actual subject.

A note on sealing cracks yourself: filling a crack changes what you can observe. It also does nothing about the reason the crack appeared, and where the reason is water getting in from above, a sealed crack can hold moisture in the wall rather than keep it out. Establishing the cause first is the part that is hard to undo later.

Where reading a crack stops working

Everything above is surface observation, and surface observation has a hard limit: the thing that decides how serious a crack is usually sits behind the coating. Whether water has been getting past the finish, how long it has been doing so, and what condition the assembly behind is in are not visible from the yard, and no photograph settles them.

Three situations are worth a look from someone in person rather than more watching: a crack that is measurably wider than it was, cracking that comes with staining, powdery deposits or a hollow sound, and any stair-step pattern or visible offset in the wall plane. The first two are about water; the third is about movement, and it is the category where the stucco is the symptom rather than the subject.

An honest word about what an assessment can and cannot conclude. Someone looking at the wall can tell you what is happening on it, how sound the coating is, and what the likely route the water is taking looks like. Some questions genuinely stay open until a section is opened up, and a contractor telling you exactly what is behind an intact wall is guessing.

What that assessment involves, and how repair and recoating differ in scope, is covered on our stucco repair page. If the cracking you are looking at is in the grey band at the very bottom of the house rather than on the wall above it, you may be looking at the foundation coating instead — worth confirming with how to tell parging and stucco apart before you conclude anything, since parging repair is a different job.

Not sure whether yours is one to watch or one to act on?

We will walk the exterior and tell you what we see, including when the answer is that it is stable and can wait. Free, on-site, no obligation.

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