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Chapter 24: The Case of the Curious Cracks, Masonry Cracks Explained

Updated: Feb 19

...It was a crisp morning as Sherlock Holmes and Dr. John Watson arrived at the quaint countryside home of Mr. Reginald Thornton...

The man, visibly distressed, paced the front porch, his eyes anxiously scanning the visible cracks in his house's exterior walls.

"Ah, Mr. Thornton, I see you're troubled by these cracks," Holmes remarked, offering a comforting smile. "Worry not. Dr. Watson and I are here to thoroughly investigate and ease your concerns."

Relieved, Mr. Thornton led them inside, where they settled in the sitting room with a cup of tea. "Gentlemen, these cracks have kept me up at night. I'm eager to hear your thoughts."

Holmes took a sip of tea before beginning his analysis. "You have three types of cracks here, Mr. Thornton: vertical, diagonal, and horizontal."

"Vertical cracks, often caused by settlement or ongoing movement, are noticeable," Watson added, his medical background lending clarity to the explanation.

Vertical Foundation Cracks can be caused by different soil types
Different soil types can cause vertical cracks

Holmes nodded in agreement. "Indeed, Watson. Shrinkage as the cause is far less worrisome than settlement. You can be reassured that vertical cracks aren't frost-related."

"Thank goodness for that," Mr. Thornton sighed, visibly relaxing.

Holmes continued, "Now, these widening diagonal cracks, especially those wider at the base, suggest settlement. Additionally, those near windows may signal weak headers."

Watson added, "Yet, diagonal cracks in poured concrete foundations, especially if uniform in width or hairline, are often due to shrinkage and pose no structural threat, although they may allow water ingress."

Impressed, Mr. Thornton remarked, "Your expertise is remarkable, Mr. Holmes. I feel much better already."

"Thank you, Mr. Thornton. It's my duty to clarify such matters. Now, observe these V-shaped cracks," Holmes pointed out, indicating a pair on the exterior wall.

"These indicate heaving, possibly from crushed mortar joints," Watson explained, providing further insight into the situation.

Heaving is when the soil swells and pushes the foundation up
Heaving can cause V cracks

Holmes continued, "Conversely, cracks forming an inverted V or pyramid shape suggest settlement or sagging in the middle."

"And what about these horizontal cracks below ground level?" Mr. Thornton inquired, intrigued by the discussion.

"Ah, those are indeed not due to settlement but are still worth noting," Holmes responded. "They occur from external pressure on the foundation wall below grade. Poor backfilling, expansive soil, and frost are common causes. Furthermore, horizontal cracks often coincide with lateral displacement, potentially leading to wall bowing and eventual collapse."

Horizontal cracks in a basement wall
Horizontal subgrade cracks

False Settlement Cracks
False Settlement Cracks are caused by inward pressure

Watson interjected, "But rest assured, Mr. Thornton, with proper attention and timely repairs, these issues can be effectively resolved."

As they meticulously examined each crack, Holmes and Watson elucidated the various factors contributing to their formation and the corresponding solutions for each. Their detailed insights, coupled with their reassuring demeanor, began to alleviate Mr. Thornton's concerns.

"Mr. Holmes, Dr. Watson, I cannot express my gratitude enough for your thorough guidance," Mr. Thornton expressed, now feeling considerably relieved. "You've truly alleviated a significant weight off my shoulders."

"It was our pleasure, Mr. Thornton," Holmes responded warmly. "Now equipped with an understanding of these cracks, you can take the necessary steps to address them and safeguard the stability of your home."

With heartfelt thanks, the homeowner bid farewell to Holmes and Watson, feeling empowered to tackle the issues at hand. As the duo departed, they exchanged knowing glances, satisfied with another successful resolution and prepared to confront their next intriguing challenge.

Holmes and Watson know about foundation cracks
Holmes and Watson teach about foundation cracks

Cliff Notes:

- Vertical cracks could be due to serious settlement if they are significantly large or show signs of ongoing movement.

- Vertical cracks caused by shrinkage are of less concern than those caused by settlement.

- Vertical cracks are not caused by frost.

- Diagonal cracks that grow in width, especially ones that are wider at the bottom than at the top, indicate settlement.

- Diagonal cracks over windows indicate a weak header.

- Diagonal cracks in a poured concrete foundation that are fairly uniform in width or are hairline-type are caused by shrinkage and do not constitute a structural defect.

- Two cracks forming a V shape indicate heaving, especially if accompanied by crushed mortar joints.

- Two cracks forming an upside-down V or pyramid shape indicate settlement or drooping in the middle.

- Horizontal cracks below grade are not caused by settlement, yet they can still be a cause for concern.

- Horizontal cracking is caused by pressure on the outside of the foundation wall below grade.

- Possible causes of horizontal cracks include improper back-filling, expansive soil, and frost.

- Horizontal cracks are often accompanied by lateral displacement, leading to wall bowing and potential collapse over time.

- Active crack indications include cracks that have been patched and reopened, sharp edges in brick cracks, no dust or debris inside the crack, and no paint inside the crack.

- Cracks that follow mortar joints do not mean the crack isn't a problem; walls crack at their weakest point.

- Indications of inward bowing at the top of the foundation include the end of an I-beam protruding through the wall and a pronounced overhang of the brick veneer in the middle of the wall that disappears at the ends (up to a 1-inch overhang is acceptable).

- Attached garage slabs heaving or settling can leave cracks.

- Parge coating on block foundation walls can crack and crumble due to moisture getting behind it during freeze-thaw cycles.

- Weep holes should exist at least every 36 inches.

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