Cracks in a Garage Floor Slab - Caused by Flooding?

Cracks in a Garage Floor Slab - Caused by Flooding?

Complaint/Observation: cracks in a garage floor slab near the entry.

Diagnostic comments:In this photograph of a cracked garage floor provided by Bob Maltempo , we both concluded that we were not faced with a structural concern. A concrete floor slab poured inside of a perimeter foundation is not normally a structural component in the building.

Significant in evaluation of these floor cracks was their pattern and location. A close examination of the crack pattern might show a combination of concrete shrinkage cracks combined with subsequent settlement or frost heave damage. It was significant that the cracks were concentrated at the entry to the home's garage. In New York, a climate that experiences freezing soil conditions in winter, it is common to see cracked garage floors near the garage entry. That's because of the combination of wet soils, frost heave, and the fact that the coldest part of the slab will be at the garage entry doors. See Frost Heave/Expansive Soil Cracks in Slabsand also Settlement Cracks vs. Frost Heaves .

Our opinion was that because of their location, the absence of settlement that might occur following flooding, the pattern which included shrinkage crack patterns, these cracks were due to shrinkage and frost heaves, not to area flooding.

The floor slab could be involved with the building structure if it were poured as a monolithic slab with an integral footing, and cracks in a such a slab would need to be followed to determine if they involved the building footings as well.

Effect of wire brushing cracks on crack diagnosis:These cracks were interesting because they had been wire brushed by the building owner's son. We're not sure why this step was taken, perhaps it was in anticipation of applying a masonry patch compound. (Wire brushing would be an ineffective preparation step.)

Wire brushing the floor slab cracks over-rode any pre-existing age-wear on the crack edges, it removed upper level dirt, debris, and it removed floor surface discoloration that might have assisted in evaluating the age of these floor cracks.

But the discovery of portions of these cracks that had not been wire brushed, and a close inspection under magnification could still provide diagnostic evidence. It's unlikely that the wire brush process reached to the very bottom of the floor cracks.

Wire brushing of an existing crack would also make it difficult to observe the wear and smoothing of the upper edges of the crack that are caused by years of foot traffic, vehicle traffic, dragging objects over the floor, and similar forces.

Flood Damaged Foundation Analysis Suggestions

Damage and Risk Assessment of Wall & Floor Cracks:

The first priority question is whether or not there is evidence that the cracks observed represent damage to the building that needs repair - that is, are the cracks cosmetic or are they more important. In the case above there was no evidence of structural movement in the foundation wall and the cracks about 1/16" wide, vertical - a low-threat to foundation walls. The garage floor was not a structural element (it is not carrying the structural loads); a cracked concrete floor slab might however be considered a trip hazard if cracks are higher on one side than the other by 1/8" or more, and in some areas floor slab cracks can increase the risk of radon gas entry or water entry.

How is the foundation wall constructed?

In the case we describe, as in most older homes, the concrete wall is constructed without internal reinforcement, placed on a poured concrete footing (not visible, but assumed).

Questions about Possible Flooding as a Foundation Damage Cause or Contributor

1. What is the crack inventory: just where on the structure do cracks appear - make a complete list.
2. What is the location, extent, pattern, and implicationof any building foundation or slab dislocation (or related components such as framing) associated with the cracks under investigation?
3. What is the evidence of a historyof foundation movement and prior repairs to the foundation. See FOUNDATION MOVEMENT ACTIVE vs. STATIC
4. What is the extent of vertical dislocation- "up" or "down" movement? See VERTICAL MOVEMENT IN FOUNDATIONSand VERTICAL FOUNDATION CRACKS andDIAGONAL FOUNDATION CRACKS
5. What is the extent of horizontal movement or dislocation- leaning, tipping, buckling, bowing in the wall? SeeHORIZONTAL MOVEMENT IN FOUNDATIONSand FOUNDATION BULGE or LEAN MEASUREMENTS and also see HORIZONTAL FOUNDATION CRACKS
6. How far below gradeis the bottom of the foundation wall - that is, how high on the foundation wall does soil appear outside?
7. How high did flood waters reachon the building? If flood waters were high on the building exterior and filled the building, and if receding flood waters left the building with no water inside its basement or crawl areas below grade (this would be unusual), the wet earth pressure remaining outside might damage the foundation wall.
8. Were flood vents installedor were there other openings that admitted flood waters to the inside of the foundation wall?
9. Is the damaged foundation wall in a heated spaceor an un-heated space. The presence or absence of heat can help establish the probability of uneven frost damage to a foundation. SeeSettlement Cracks vs. Frost Heaves