# Corner Cracks



## ax525

As many more houses in South Texas, our house suffers from exterior corner cracks in the concrete slab. All corners with cracks were covered with concrete when we first moved in three years ago. About one year ago, one of the corners separated from the house (see link), but no other problems have been seen (no cracks in the interior corner, walls, window or door frames, etc). I'm concerned because the "crack" went beyond the slab and reached the masonry. Any tips in how to repair this problem? (I tried before, but the result is obvious). Is it time to call a contractor?

http://img412.imageshack.us/img412/6835/cornercg4.jpg

Any comments will be appreciated.

- Frank


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## glennjanie

Welcome Ax:
Concrete and masonry are subject to cracking; this one is very small and is of no consequence. I would'nt worry about it.
Glenn


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## STG

I conducted a repair on my house this weekend for this very same issue.  I chiseled out the crack a bit with my cold chisel - but didn't go all the way into it.  The crack was quite small - but there was an area a bit deeper that had a 1/8" crack in it that I did not go deep enough to completely access.  I was concerned about breaking the concrete corner completely off the foundation.

The crack is diagonal on both sides of the corner of my house.  It starts about 10" from the corner and works its way to the corner edge on both sides.  When I chipped off the cement overcoating, I found that the crack was very narrow - the cement was actually touching below the surface with no visible gaps...with the exception of the area with the 1/8" gap.  

The larger area was at the very top of the crack on the side of the house that gets the most sun.  I'd opened up the top of that crack area a bit (about a 1.5" wide x 1" deep section).  The larger crack was visible from this area.  

Once I'd verified that, with the exception of that larger cracked area, the cracks were present, but the concrete was touching, I attempted my repair.  

First, I mixed up Quikrete vinyl concrete patching compound.  According to Quikrete's website, this stuff has a compressive strength of 3000psi at seven days and 5000psi at 28 days.  I packed it into the area I'd opened up at the top (and from where the larger crack was visible) to the point of refusal.  That is, I couldn't stuff any more of the crack repair in.  Whether it made it to the larger crack is unknown.

I then covered the rest of the crack with the the patching compound.  The crack was covered in an area about 2" wide and 1/4" in depth.  

For what it's worth, 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. The cracks in the corner appear to be limited only to the outside - I pulled up the carpet and found no cracking on the interior slab in that area.

Was this a decent repair?  

Should I be freaking out about this type of wedge crack?


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## STG

I've uploaded photos of the repair.

The first two pictures are of my house after repairing the crack in the manner I described earlier.  

http://i299.photobucket.com/albums/mm293/southtexgopher/IMAG0002.jpg

Other side:

http://i299.photobucket.com/albums/mm293/southtexgopher/IMAG0001.jpg?t=1213539511

The third photo is of a home near mine that has not had any repair done.  This crack is in the far left hand side - mine did not look as bad as this prior to the repair.  There is also some breakage on the top where the concrete meets the brick facing.  My house also had that issue.

http://i299.photobucket.com/albums/mm293/southtexgopher/IMAG0003.jpg?t=1213539543


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## glennjanie

Welcome STG:
Your corner repair is a beautiful piece of work. I'm sorry I put Frank off about his corner; I think he could use your method on his home too.
The parts that are cracking and popping off have one thing in common, there doesn't seem to be any agregate (rocks) in the concrete. This is the result of attempting to drag the concrete around too much in the forms or the truck gets empty and the pour is continued an hour or so later (cold joint). The patching material and methods appear to be working well and I would recommend both to homeowners having the same problem.
Glenn


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## STG

Thanks for the welcome and the feedback.  

This happens on many houses here, Glenn.  What people "in the business" have told me is that this results from the brick pushing against the corner of the foundation.  It actually pushes the corner out of the slab.  I have a few broken bricks, too...but I think that should be OK. They're level and they have not separated.  

The repair I did sound like a sensible thing?  

I've been a little concerned about the 1/8" crack I saw inside the area I chipped out - it almost seems like there was a void in there.  I'm just hoping the Quikrete I put in filled it to some degree.

Frank, if you're in south Texas, feel free to email me and I'll talk you through what I did.


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## STG

Wonder of wonders...

I just talked to my neighbor who's been doing a bunch of work on his house this weekend, too.  Turns out that he's a retired concrete contractor.  

He says that there's little one can do other than cover up this sort of thing.  It's a cosmetic issue and can't really be repaired - just bandaged.  We're going to attack this next weekend and make some repairs to other hairline cracks as well as this one in both of our foundations.  

Wow.  

How ironic to learn that only after making the repair.


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## kflack

I have a similar problem. House built in 2004....

Here are a few pictures of the problem.

Just called the contractor but not sure what needs to be done.

Note; Resent activities in the area
1) Road Paving last year 25 ft away  (Steamroller Vibrator shook whole house)
2) New house being built next door (Alot of concrete trucks stopped with 10 ft of the broken corner.
3) 3 years ago a large drainage ditch installed within 10 ft of corner house.
4) Drain pipe drains within 2 ft of corner.

http://picasaweb.google.ca/kflack/Foundation#5255173895223416594

http://picasaweb.google.ca/kflack/Foundation#5255173916835472370

http://picasaweb.google.ca/kflack/Foundation#5255174082099195122

What would your recommendations be.....

Note: Evening temperature just started to drop below 0 deg (freezing)


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## glennjanie

Welcome Kflack:
The cracking problem is not a weight problem, nor are any of the other things the reason. In my opinion the problem is in expansion and/or poor placement of re-bar in the concrete (re-bar controls expansion, so its all the same).
The corners could be chipped off enough to expose the re-bars fully and rebuild it with the above mentioned 'hi-strength' premixed concrete. However, it is really just a cosmetic thing and any patch will be simply cosmetic also. The houses will probably stand for many years without any help but some color matched caulk would help to hide the problem.
Glenn


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## mzullig1

I'm guessing that my issue with cracked foundation at corner of my house is of no issue as well.  Can someone give me their assessment if this is an issue?  Below are pics of the cracked corner at foundation slab.

Thanks

Mark


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## BridgeMan

Mark,

Thanx for rejuvenating this old post.  And I'd like to share my opinions on the nature of your concrete problems.  The deterioration visible in your pix has the appearance of concrete that was exposed to freezing temperatures at the time it was placed.  That is, the matrix is crumbling, and losing its grip on the aggregate.  That is something that often happens at corners or the ends of a concrete run, where there is more exposure to freezing than in the middle of the run (and less benefit from the mix's internal heat of hydration, being away from the center of mass).  It appears whoever placed your foundation didn't take adequate precautions to prevent the mix from freezing before it set up, such as using blankets or applying external heat.  Over time, the situation will continue to degrade, particularly if the corners are exposed to moisture and repeated freeze-thaw cycles.  There could be other causes as well (ASR, a reactive aggregate reaction, or even sulphation), but they would most likely be visible throughout the concrete run, and not just prevalent at the ends or corners. 

I would not call your situation simply "cosmetic."  If not corrected, eventually there will be a tendency for the brickwork above the failed corner to settle enough to slip or break away from the internal metal ties that hold the brick against the house's wall.  Cracked mortar joints are an indication that this has already started.  Your house will not fall down, but eventually you will be faced with a hefty bill from a masonry contractor to properly repair the damaged brick and concrete below it.

Repairing the corners now is a good option, and can be performed by anyone having moderate construction skills and common sense.  Obtaining quotes from experienced and knowledgeable foundation repair firms would be a better option, if your finances allow for the work to be done professionally.


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