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Hairline cracks in foundation


I've been reading all the great answers on this site and I've found it very helpful.

But...I'm still quite nervous about some things with regard to my own house. My house is a 1600 square foot, single-story home on a slab foundation. Three sides of the house are brick - the back of the house is siding. The foundation is coated in a stucco-like concrete parch coat. The house is located in north-central San Antonio where the soils are a combination of clay and limestone. The limestone bedrock is about 10 inches below the ground surface.

There is no interior damage to the wall or ceiling sheetrock, all the doors and windows function fine.

I have hairline cracking in three places that I'm concerned about. The cracks are all about 1/32" in width or less.


Two of the corners have diagonal cracking running at a 45 degree angle beginning near the corner of the foundation and continuing toward the inside dimension of the foundation. The cracks are well below 1/16" in width and the width the same along the entire length of the crack. Not sure if this is important to mention, but these corner areas are only in the areas of the foundation that are topped in brick (that is, the walls above the areas have brick facing).


Last night I found another crack in the foundation wall of my garage. The foundation rises from the garage floor to a height of about 24" where it achieves the same level as the floor of the house. There is a hairline crack running from about three from the floor all the way to the actual top of the foundation wall. This crack continues into the concrete under the carpet inside the house for about a 10" length.

I broke out my cold chisel and hammer last night and cleared away the parch coat and a bit of the concrete. The hairline crack in the garage foundation wall runs through the parch coat and into the foundation about 3/4" - and then it stops. I ended up clearing away a V-shaped area of the concrete 3/4" deep at the deepest spot and about 3/4" wide at the outer limits of the "V" (the inner limit was 0" wide). After doing this and satisfying myself that the crack didn't extend deep into the foundation, I sealed up the area I'd chiseled with Quikcrete concrete repair ( QUIKRETE® - Concrete Repair ). I applied this by packing the area with the product and then smoothing it with a putty knife.

At the top of the crack - in the house itself - I chiseled out a bit - and the crack's depth is only about 1/16" at its worst. I left that alone.

The cracks in the corners have been temporarily sealed with the Quikcrete product as well - I've had quotes for repair of that using lathe and a new concrete parch coat.

My questions...

1. Should I be freaking out? I'm losing sleep over this and stressing out constantly.

2. Did I do anything stupid in the garage by chiseling out the crack and patching it?

3. Does the repair that the contractor has told me about make sense?

Re: Hairline cracks in foundation

Great details ... however ... an important piece of information that might help ... how old are the house and the garage? :)

Re: Hairline cracks in foundation
canuk wrote:

Great details ... however ... an important piece of information that might help ... how old are the house and the garage? :)

Thanks for responding.

The house was built in late 1995, so it's just under 13 years old. I've been in the house for a little over six years. The cracks in the corners have been there since I moved in. I can't say that they're getting worse...I plastered over the corner cracks when I moved in and became concerned when I saw they'd re-cracked in the same location...noticed it while landscaping.

I don't know about the one in the garage - it may be that I simply didn't see it, since it it's right behind where we keep our trash can and recycling bin.

Re: Hairline cracks in foundation

It very difficult to say as to how serious if at all the cracks are.

Concrete is an incredibly strong material .... however .... it's a rigid material and isn't very flexible.
In your case you have a slab on grade and if the soil underneath has a tendency to move this may produce slight stress cracks in the concrete because it isn't flexible.
Clay soils are always an issue since they absorb water and expand then shrink when dry.

Many things may be the result of the cracks you see. This could have occurred as a result of settling from when the house was first built till now.
Many other factors come into play such as how well the base was prepared before the concrete pour when the home was being built.
Concrete will also shrink as the water evaporates during the curing process and may sometimes result in slight cracks.

Judging by the size of the cracks they may be just slight stress cracks and if they don't appear to be growing in size ...... width and length ... it may be nothing to worry about.

From your description on the method for the parge coat ... it sounds as though they recommend this to prevent the parge coat from cracking. If the parge coat is simply applied to the concrete slab .... sounds like this is the original method .... any cracks that occur in the slab will telegraph through the parge coat. The mesh is being used to re-enforce the parging in hopes it won't crack.

If you are in doubt as to the stability of the concrete slab you should consider having a foundation contractor evaluate the situation first hand . It's difficult to say over the internet as to the situation there.

Just some thoughts. :)

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