Often asked: What Makes Concrete Crack?

Is cracking in concrete normal?

When you see a crack in your concrete slab or wall, your first assumption is typically that something has been done wrong–but that’s not always the case. Actually, concrete cracks are very common, some are even inevitable.

What is the most common cause of cracking in concrete?

Probably the single most common reason for early cracks in concrete is plastic shrinkage. When the concrete is still in its plastic state (before hardening), it is full of water. This water takes up space and makes the slab a certain size. As the slab loses moisture while curing it gets a bit smaller.

Why do concrete cracks appear?

Concrete expands and shrinks with changes in moisture and temperature. The overall tendency is to shrink. Shrinkage is the main cause of cracks, when concrete hardens it evaporates the excess water and thus shrinks, so lesser the water content, lesser is the shrinkage.

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When should I be concerned about cracks in concrete?

A crack in a slab of 1/8 inch or less is typically a normal shrinkage crack and not a cause for concern. If the crack is larger or growing larger (an “active” crack), or one side of the crack is higher than the other, then you may need to have the work reviewed by a structural engineer.

How do I keep my concrete slab from cracking?

4 WAYS TO PREVENT CRACKED CONCRETE

  1. Start with a sound subgrade. Make sure the subgrade is compacted.
  2. Modify the concrete mix. Use a low water-to-cement ratio.
  3. Install joints. Be active in deciding where control joints will be placed.
  4. Properly cure the concrete. Properly curing concrete slabs: Why and how to cure.

Can you fix cracked concrete?

Wide cracks in concrete are best patched and sealed with a concrete patching compound. Smaller cracks, less than 1/4 inch wide, can be repaired with a concrete caulk or liquid filler. Patching compounds typically are mixed with water and applied with a trowel.

How thick does concrete need to be to not crack?

Applied-load cracking.

In residential concrete, 4 inches is the minimum thickness for walkways and patios. Garage slabs and driveways should be 5 to 6 inches thick if any heavy truck traffic is anticipated, otherwise 4 inches is adequate.

Can you pour new concrete over old cracked concrete?

There are situations when pouring new concrete isn’t the most suitable option. For instance, surfaces with larger cracks, heaving or settling conditions, or where height cannot be raised, replacement is a better solution. However, in most cases, you can pour a new layer of concrete onto the existing one.

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How much concrete cracking is acceptable?

In the case of a wall, if a crack is not structural, is not too wide (the acceptable crack of a crack depends on who you ask and ranges from 1/16” to 1/4”) and is not leaking water, it should be considered acceptable.

How can you tell if a concrete crack is structural?

Characteristics of structural cracks

Horizonal foundation cracks in walls, with or without bowing – These are almost always structural. Cracks in a ceiling that run across the ceiling and down a wall – These are usually structural cracks.

Are cracks in concrete bad?

Shrinkage cracks are common and can occur as early as a few hours after the slab has been poured and finished. Usually they are not a threat to the structure. In hot weather a concrete slab will expand as it heats up and pushes against any object in its path, such as a brick wall or an adjacent slab of concrete.

How do you stop walls from cracking?

Build in movement joints as construction proceeds. Spacing between these joints should never exceed 15m in unreinforced walls. Use slip planes – these enable elements of the construction to slide in relation to each other to help reduce stress in the adjacent materials.

How do you fix cracks in concrete garage?

Always use an epoxy, polyurethane, or polyurea based crack repair or crack filling compound that is sandable. These cure and harden at a strength greater than concrete and will prevent water intrusion as well. You can grind or sand them flush with the concrete and they will accept paint or an epoxy coating.

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Should you fix hairline cracks in concrete?

Broken Rule One: Hairline cracks are not worth the trouble fixing. Did you know that just about every crack in concrete started out as a hairline crack? Some so fine, you can not even see them with the naked eye. Cracking naturally occurs in concrete slabs as the concrete cures and shrinks.

How do you know if a foundation crack is serious?

While you’re under your house in a basement or crawlspace, you’re looking for any cracks or signs of damage. If you find long horizontal cracks, leaning, or bowing walls, you are in dangerous territory. If the foundation walls are made of concrete block, the cracks may look like stair-steps.

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