Why Your Basement Floor Has Cracks And Ways To Fix It

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A concrete basement floor often feels pretty stable (which it should), but we don't always appreciate that it's a dynamic structure subject to constant pressure and changes in temperature and the soil underneath. Cracks in the surface can be scary to see and might even conjure images in your head of costly repairs, just like those you might anticipate when you identify cracks in your foundation. But we can ease your mind a bit by saying that most cracks are not structural failures; they are normal and non-threatening and simply result from the floor's natural curing or settling. However, if there is a crack in your basement floor, properly identifying what type it is will let you know how to handle it (or if it's minor enough to not require repairs).

First off, there are two types of cracks that fall into the harmless category: hairline cracks and spalling or flaking. Hairline cracks are the most common and just look like thin shallow lines often less than 1/16 inch wide. They are typically shrinkage cracks that occur during the concrete's initial curing process as water evaporates. Hairlines are surface-level and rarely cause damage to the slab's structural integrity. Similarly, spalling and flaking are not structural concerns but also just a surface-level defect. Spalling occurs when a thin layer of the concrete surface chips or flakes and looks like a shallow dent. This is usually caused by too much water being added to the concrete mix, poor finishing techniques, or exposure to freeze-thaw cycles. While both hairline cracks and spalling can be unsightly, they don't necessarily need any professional repair beyond aesthetic resurfacing.

While surface-level imperfections can be ignored, any crack that widens significantly moves out of the purely aesthetic fix category and should be addressed to maintain a healthy home environment. Specifically, cracks that measure ⅛ inch or wider signal a bigger and more problematic movement in the concrete slab even if they aren't huge structural risks yet. These moderate-sized cracks are usually uniform in their width and often caused by minor shifts in the earth beneath the foundation (a normal occurrence for most houses over time). And beware, because even though they might look minor, these cracks create a clear pathway for bigger issues beyond appearance.

The biggest concern with this crack type is that it makes it very easy for soil moisture, pests, and radon gas (a naturally-occurring radioactive gas that's a significant health hazard) to infiltrate the space. The appropriate fix for these moderately serious cracks is just sealing them up yourself. All this involves is giving the crack a thorough clean to remove dust and debris and injecting a quality concrete crack filler, such as DAP Concrete Crack Filler, or epoxy sealant. The goal at this level isn't to fix a structural issue but just to seal the basement environment from hazards. Taking care of these cracks promptly with a good concrete repair product stops them from worsening and keeps you (and your home) safe.

When a crack is larger than ½ inch or features one side that's taller than the other (called vertical displacement), it crosses the threshold into what's considered major structural issues. These need professional attention immediately. A crack of this size indicates a serious problem with the foundation or the soil beneath it; this could be caused by things like water pressure or expanding clay soil.

And unfortunately, this level of structural issues will hardly ever have a quick and easy resolution like sealing the floor. Instead, you'll need to call in the pros. Most likely, they will have to set up a complex engineering plan that focuses on leveling and stabilizing your basement floor. For uneven concrete slabs, professionals could possibly use a technique like polyurethane foam injection to lift the sunken side of the slab so it lines up with the other side again. In more severe cases, you may even need to fully replace the damaged sections of your basement slab. While some cracks don't need any repairs or only require a quick and easy sealing, remember that large cracks are much more serious and even why some people think twice before installing concrete flooring in basements. Taking professional steps to address any major basement floor issues you come across in your home is the best all-around way to protect your investment and ensure a solid, stable foundation for decades to come.