Mysterious Cracks Ruin 25-Year Old Home

There could be 3 causes that I'm aware of, but I really need an accurate description of the cracks, width, depth, location, shape of cracking, are the cracks increasing in size or quantity, etc., as well as your geographic location and climate..It could be...D-cracking...D-cracking is a form of freeze-thaw deterioration that has been observed in some pavements after three or more years of service. Due to the natural accumulation of water in the base and subbase of pavements, the aggregate may eventually become saturated. Then with freezing and thawing cycles, cracking of the concrete starts in the saturated aggregate at the bottom of the slab and progresses upward until it reaches the wearing surface. D-cracking usually starts near pavement joints.

Or it could be...Thermal cracks... Temperature rise (especially significant in mass concrete) results from the heat of hydration of cementitious materials. As the interior concrete increases in temperature and expands, the surface concrete may be cooling and contracting. This causes tensile stresses that may result in thermal cracks at the surface if the temperature differential between the surface and center is too great. The width and depth of cracks depends upon the temperature differential, physical properties of the concrete, and the reinforcing steel.

Possibly...Alkali-aggregate reaction: Alkali-aggregate reactivity is a type of concrete deterioration that occurs when the active mineral constituents of some aggregates react with the alkali hydroxides in the concrete. Alkali-aggregate reactivity occurs in two forms—alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR).
Indications of the presence of alkali-aggregate reactivity may be a network of cracks, closed or spalling joints, or displacement of different portions of a structure.

It could be a combination of any or all of these, combined with subgrade settling...The question is how deep are the cracks and are they growing? Are they just cosmetic, or are they structurally threatening?

I've been told everything from my house could implode to not to worry about it! I'm in Atlanta, so although I didn't understand most of what you said, extreme tempertures are probably not an issue. My house is a "five four and a door"....walk in to a foyer, living room to the right, dining to the left, den behind livingrm. kitchen behind diningrm. The crack in the livingrm is straight across. The crack in the den is curved. The foyer, kitchen and diningrm all have uneven places! The one in the livingrm was there 12 yrs ago when I bought the house but has gotton worse recently. The others are all recent.

I hate to say it , but recent movement doesn't sound good . Solareagle makes valid points , but they don't sound to me as if they are the cause (not after 25 years ) . Also , am I right in thinking/hoping you didn't know about the Living room crack when you bought the place ? The Geo-tech will have considered the ground condition (eg stuff like clay is a nightmare , it can heave/shrink years after a building is put up). Is the structure such that you would see movement (cracks in wall /ceiling plaster , doors jamming ) ?.

Depending on your level of worry ,you could monitor movement yourself (a serious investigation would probably do this anyway ) . Use a nail gun to put some discreet studs either side of major floor cracks , and use precision vernier or calipers etc to monitor displacement against time (don't ignore that cracks may move along each other as well as apart ). A precision of 1/10 a mm is what I would track (once a day).

Are there any external influences on the house/property , and do you have neighbours with similar things going on.These are the kind of things I would be asking. At the end of the day , this sounds like you need somebody on the spot with the expert knowledge (though I appreciate you've tried this ). Do you have legal recourse against the people who sold the place to you (for non-disclosure of a problem ).

I agree that it is wise to try and understand the situation before getting involved with the insurance people , but if nobody can ID the problem it may have to go that way. I'm sure you've already figured that they wouldn't like it if they thought you delayed telling them , but I agree with your approach. Watch your post here for a while , and you may get somebody who recognises the symptoms and can help.

Good luck ,Kris

Yes, the uneven levels you describe are most certainly due to support problems... usually caused by settling or washout of soils and subbase materials, this can cause a variety of problems, from cracking and performance problems to structural failure. You can beef-up your knowledge with some research...Here is a cheap primer...

http://www.cement.org/bookstore/profile.asp?itemid=IS177

This certainly requires close monitoring, as was suggested...And I think the suggestion of checking with neighbors to see if they are experiencing these problems, is also an excellent idea...Perhaps someone has already encountered this and found somebody qualified in the area to deal with it...Good Luck

Was the concrete base laid on to a sand base? If so this could be the cause.

There are many possibilities as to why you may have developed these cracks. If the walls and ceilings show no cracks, then I doubt that it has anything to do with settling. Settling is usually uneven and creates torque on the structure which would show up in the walls and the ceilings.

The two possibilities that come to mind are that nearby construction may have required excavation and they may not have properly retained the walls of the excavation and the soil/earth may have shifted. This could cause the kinds of cracks you described.

Another possibility is that near by blasting (again from constructiion) may have caused a ripple in the soil that formed the cracks. Check to see if any significant construction nearby caused significant excavation or blasting. The ripples from blasting could have been as much as 1/2 mile or further away.

Good luck

Where do you live? residential Alanta or suburbia?

How deep is the bedrock?

Are they a full 1" wide?

Give me Lat and Long I will look up a UGS survey.Or you can:

Floors are my business.

http://neic.usgs.gov/neis/epic/epic_rect.html

I am wondering if the house is heated from within the concrete? Our welding shop has walls 8'high and 1'thick...I re-inforced the concrete with 5/8 rebar every 10" vertical and every 12" laterally. I thought this would never crack but alas...directly behind the radiant heat source (wood stove) and the exhaust stack there apeared a vertical crack the entire height of the wall! nature's own expansion joint. Lots of rebar helps to keep the temperature the same throughout the wall so there are no cracks EXCEPT in the area described. Possible there is a thermal contradiction in your concrete? or not enough re-bar? If a vibrator was used incorrectly after the concrete was poured, the higher density aggregates can settle to the bottom causing weakening of the poured concrete particularly in areas where the vibrator was used excessively. For a forensic exam do a core sample in the area where cracks appear then measure aggregate dispersion versus size...also shape of aggregate can affect strength, sharp stones giving more strength than rounded. let us know the solution to the puzzle when you find out.

I agree with vince-the-welder regarding having an analysis performed on some full depth core samples.

Other problems that may be identified are; insufficient or unsound aggregate, inadequate portland cement, overwatering of the mix at time of pour, which can be evidenced by voids in the concrete left by evaporation of excess water.

The things I haven't heard in this discussion; are the levels of the now separate slabs the same or is there a significant sign of settling? And, are you seeing any evidence of a wire mesh reinforcement in the now visible separations?

I do this for a living (residential structural inspections, that is) and am a licensed Structural PE in MO. You are almost certainly experiencing 'heaving', which is when water reaches expansive or 'plastic' clays beneath a slab assembly. In extreme cases heaving can even lift the perimeter footings, but that is less likely. Plastic clays have a very fine particle size and a high affinity for water, swelling dramatically when exposed to it. Your house is probably not suddenly experiencing densification settlement (where the soil compacts over time due to a constant pressure such as under a foundation wall) after 25 years. But it is likely the backdig around the house (the soil around the perimeter of your foundation against the outside of your house), dug to install the foundation originally and piled back against the outside of the foundation uncompacted, has densified over time because it was disturbed during the original construction, and settled down against the foundation making a great place for water to stand instead of running away properly (IBC calls for a minimum fall of 1" per 12" for a minimum of eight feet away from the foundation). This causes poor drainage that routes water to the foundation wall, stands against it subgrade and pressurizes its way under the perimeter footings to reach the plastic soils. Then the heaving begins. This often DOES occur after at least 10-15 years because it takes that long for the drainage to get bad enough around the house. I've seen this LITERALLY thousands of times, because, as I said, that is what I do for money. You will need to ENSURE you have NO poor drainage details around your house, and WAIT at least two years for it to revers itself. If it is too bad it will NOT reverse itself and you will have to remove and replace the heaved and broken floor assemblies IF you want level slab floors. Now, there is another possible source for the water, and this is a LEAKING plumbing supply line UNDER the slab. Have a plumber come out and PRESSURE test your supply lines to see of you have a sub-slab leak. That would DEFINITELY have to be repaired ASAP to prevent ever worse damage toyour home. And that would definitely cause the heaving if it is present. But you have heaving.

I was Listening and thinking.

I want to help out.

Before that please reply following Q's:

Q1 <on the first level of my house, built on a slab.>: First Level in Atlanta Ga . parlance is --the Ground Floor ? Means 1' to 3' above the walkway-coming in?

Q2 If that is so (Ground Floor), Do you have large growingtree next to house?

It is happening in mine .

Large root striking out radially and cracking up the floor. I know this - but I won't touch my tree!

Q3. If First Level is the floor above the car garage and there are no cracks seen at the bottom face then your problem Alkali aggregate reaction.You need to put a fresh prop from Ground at centre below each room.

Please let us know. There is a solution when we know the problem.

BR

I have significant experience with 'expansive soil' causing structural problems like those described. 1) can you see reinforcing steel in the cracks?--should be able to if not--is there any?

2) Have you had the sub-slab soil tested by coring?

3) Is the movement confined to open areas of the floors? or are the walls also moving?

4) How thick are the floors? Have you had them cored and compression strength tested?

If the entire structure is moving(cracks in walls, wall and ceiling joints etc), it is possible the house sits on top of a fault line and the ground underneath is shifting. If that is the case, sorry, no cure.

Have you felt any tremors? Have you noticed any increase in the number of dead animals around your house? Does the floor sometimes feel warm and do you occationally smell sulfur? Have there been any spontanious fires in your house?

First thing first. Do the interior walls look like there's a space between the slab and base of the walls. Are the footing and foundation walls cracking and/or sinking. Is the house in location where you have real winter with up to 36" of frost in the ground. Was the foundation and slab poured on frozen ground with a high moisture content. When the ground thawed the slab would drop and everything would move and the slab will crack especially if concrete slab was poured with no embedded wire mesh. If the problem is organic debris then your problem might be greater. If the house is in a location where frost walls aren't required do you have water flowing under the slab washing out the fill?

The bad news is I don't think your insurance will cover any of these issues.

I heard of a case where, in a split level home, some 2 wooden poles used for pouring the foundation were left in place. The expansion of this wood caused the foundation to split at the divide of the two levels causing a large crack through the foundation and concrete walls of the house.

I have worked with concrete for many years both as a finisher and in delivery. The most likely cause is laziness on the part of the finishing crew. Many times when the concrete mixture is delivered to a home slab pour, the crew in charge of the finishing will add a LOT of water. This helps the concrete flow to the outer perimeters of the forms with less manpower necessary. It also causes nearly all the rock in the mixture to settle to the bottom, weakening the structural integrity. Easier on them - lower quality for you. The best way to know for sure is drill a core sample - check the yellow pages under concrete drilling. Good luck

-John

I know! I know! Your house was built on the ancient burial grounds of the Slapaho tribe and their restless spirits are vandalizing the place. Wassa matter, didn't you ever watch Poltergeist?

But really, the problem could be one or more of many things as mentioned by the previous comments. I had a similar problem with my garage a few years back. It turned out there was a natural aquifier running underneath the area where my detached garage is, about 80 feet below the surface (how the geologist figured it out I'll never know). There was a bit of erosion deep underground and as a result of the weight of the garage, there was some settling.

Needless to say, it was expensive to fix. I wound up having to tear down the garage and build another in a different spot on my property. What a pain-in-the-a** THAT was! I hope you find the problem and it doesn't cost an arm and a leg. Good luck.

We just have deep mine workings to fall into, Britain is riddled with them. We now have to supply all information to the buyer before making a property sale and if any thing happens it can cost several arms and legs to correct it. There is aspecialised mapping site set up to help people find out where the trouble spots are located. House values can quite literaly go through the floor.

I hadn't heard of this mapping service you mention . Post nationalisation detail , 1947 , would probably be reasonably documented . But extra detail from pre 19th C would presumably be mapped as found (ie too late ) ? I know that the (then ) NCB got ****ed a few times on opencast , when they came upon ancient bell mines.

I think a bigger worry for UK house buyers is Argon gas . It's now common practice for house transfers to be subject to survey . It doesn't even matter if your not in a hot spot (such as Cornwall/Scotland) for rocks such as Granite . Rock used in construction will be questioned. The conveyancing Solicitors etc must love this . The problem is easy to detect and solve , but a house sale of say 250,000 GBP can be complicated by a minor detail that can be sorted out for a few thousand pounds. On top of that , the Environment Agency issue standing Flood-warnings like confetti.

Hi,

In Colorado there is bentonite soil in some places. It swells up when wet. Have you had a lot of rain lately? That could explain it. What do you mean by a concrete slab? Are there footings with the concrete in between, or was the slab poured first, and everything built upon it after? If so, how thick is it? I went to 1st grade in an old school house with a 1 inch crack in the concrete floor, but it was probably 100 years old or more. I wish you well.

S

"Bentonite" is a type of the expansive clays that the engineer mentioned in #11. I've seen the damage that these soils can do to slabs and foundations - it's quite amazing. The local public works department should know if those soils exist in your area (or they might have been trucked in as fill). If expansive soils turn out to be your problem, first dry out the subsoil per the engineer's recommendations.

If that works you could level the slab surface with a thin topping slab. If it does not dry out, then you will have a major floor reconstruction project to correct the problem.

I'v worked in the trades for over 35 years, the one thing I have learned is the earth holds many secrets. Call a Hyro. concrete slab leveler out and forget about it.

What type slab is it? Are there footings under all roof bearing walls? (expansion joints at the bottom of all such walls?) Or is the foundation a monolithic slab? (Probably is: relatively inexpensive, shallow, common with southern residential building in recent decades.) Is damage to house caused by the foundation also being noticed: noticably growing wall cracks?; doors getting hard to open/close?...)

Is the house a recent, classic southern style? (Where classic southern includes: hip roof with extended eave overhang to shade the walls.

You mentioned terrain slope/good surface drainage. This leads to the assumption that eave gutters and downspouts are also installed. True?

...in the meantime, here's something to read over:

http://www.homeinspectioncourse.com/Other/foundations.html

Now from another angle...

Did the inspection report when you bought the house make note of the foundation/slab failures? (And, did you sign off on the report--thereby possibly waiving any exceptions?) It should have...(and if so you should not have...without getting paid or getting assurance (insurance) for full value) and you might possibly have a cause of action...(because sometimes the slab can be repaired; sometimes the house must be removed to effectuate repair or replacement; so if it can't be repaired in situ (or even if it can) you will want to find the liable party. Why? Because if you (or you heirs/legatees) ever (intend to or need to) sell the house you could become the liable party...or be stuck with an unsalable property (a situation which confronts uncounted numbers of lucky, but not so lucky, heirs and legatees). Has the mortgage/homeowner's insurer been apprised of the situation?

How long have you tracked this problem...in other words, how long has this been going on; when did it start...because, as said by another post-er, if it is now stabilized, the best course might be to just cover it up and live (and/or die) with it.

If not normal settling, or soil instability, have your experts (or actual building experts per se) considered wind loading; from tropical storms moving through or near the area? If wind-induced flexure damage appears above ground, it is not unreasonable to surmise such (ignored-during-construction) stresses could be imparted to the foundation. Just a thought.

The flip side to soil expansion of clay due to excess moisture, is contraction under drought conditions. Based on the last 2-3 years here in SC, 160 miles away, that is a likely possibility as well. This will cause subsidence.

exactly...this is why gutters and downspouts are not always called for; but they're fitted anyway because..."everyone" does it that way...or says that's what houses must have, without ever saying why.