Poured concrete foundation cracks


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Old 01-29-13, 05:15 AM
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Poured concrete foundation cracks

I have searched this forum on this issue but nothing that would satisfy my problem (curiousity).

I have a poured concrete foundation, 12 year old house located in Nova Scotia.

Although I have a number of vertical cracks in the foundation that you can 'see', I have a multitude of very tiny cracks that begin at the top of the foundation wall (as viewed when you look under the house siding with a mirror) and meander down about 3...sometimes 6 inches and then either stop, or disappear. I say disappear as I can no longer see them...even with a magnifying glass.

These cracks are the consistency of a pencil line...they are not stepped, but are obviously wider at the top than at the bottom as my reference to them "disappearing" as they move 'south' of the top of the wall.

These cracks are easily missed on a regular foundation inspection as i had to basically get very close to the foundation and inspect with a flash light (and sometimes a magnifying glass to even see them).

These cracks have also been on this house since i bought it (2009) as I took pictures of all the exposed foundation at this time. By looking back at the photo;s and zomming in...i can plainly see the existing crack, therefore it is nothing new.

These tiny cracks also seem to occur at the outer ends of the foundation wall run...ie...there may be some small visible cracks at the middle (nothing structual as I had these checked out by an engineer before I purchased)...and when I say outer ends i do not mean at the 'end' of a wall run, but rather around the last third of the wall in question.

Some of these cracks are spaced 2 feet apart, some are 3 feet....

There may be more...but i have not documented them as of yet.

I am curious if this is what is referred to as concrete 'curing' and also interested to know why these cracks would not continue ...or at least be visible...all the way down (vertically) the foudation wall.

thank you all in advance
 
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Old 01-29-13, 06:23 AM
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it is possible that the tiny cracks you are seeing are shrinkage cracks that correspond with the location of the anchor bolts. As with anything in a house you should keep an eye on them but I am ALMOST positive you have no worries. If you have to take a magnifying glass to find problems you are way ahead must of us who have old house issues staring us in the face.

It is good to try and uncover little problems before they become bigger problems but in my experience a magnifying glass is not an essential element in a home owners tool belt.
 
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Old 01-29-13, 07:22 AM
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Have you noticed if the cracks have gotten any worse since you have been in the home?

The minor cracking could be as a result of the conditions when the house was being built. If it was cool and wet when they poured the concrete, too much add mixture (generally from trying to rush the pour and build), too hot (would say dry, but I've never seen it be too try in NS), or a number of things. I know the air has a lot of salt in it, which can cause some havoc with things (like my car when it was parked in Sidney for 2 months). I don't know if salt would have any major effects with the add-mixtures they could have used.

I would suggest monitoring them and watch for change. Also take note if there has been any water issues in the basement. If the cracks don't get any worse, I wouldn't worry about them. Maybe use a sealer on the foundation and move on.
 
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Old 01-29-13, 08:01 PM
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picture

Thanks for all the responses so far.

If you read my post, the cracks in question have been there for 4 years that i know of...as I have only owned the house for that length of time....

I also mentioned that I 'documented' the entire foundation (that which i could see) 4 years ago and I am comparing cracks that I find to the pictures...and to my astonishment...a crack that seems to have appeared yesterday have actually been there all along (as confirmed by the 2009 photo's).

Therefore...to answer the question...they have not grown or gotten wider to my knowledge...(maybe more pronounced in the winter as compared to the summer(?))

Regardless...i have included a pic of one particular crack...to the trained eye it is easy to see...look in the middle of the photo and follow the top of the foundation wall down to the 'divit' (like an air bubbled in the foundation).

This particular crack...just like the rest of them...starts at the top...and meanders down until you can't see it anymore.

All comments and input is appreciated...like I said...I just want to be able to identify this type of cracking...ie: does this look like a shrinkage crack to the trained professional as I have quite a few of these.

I DO have some structual cracking in foundation and like I said...I DID have a training engineer inspect these cracks before purchase. Also there is no existing crack in this foundation that has 'moved' from it's original shape...as of yet fingers crossed.

Sniper has hit the nail on the head so far by commenting that professionals don't usually carry a magnifying glass in there tool belt....I like this remark and it makes sense to me.

This foundation was poured in the summer time (year 2001)...but I of course do not know the mixture...just that it came out of a truck.

Again...thanks in advance to all the responders...
 
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Old 01-29-13, 08:07 PM
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pic info

I should also point out that most of the other cracks are more pronounced...but all start at the top and meander down and sort of disappear.
 
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Old 01-29-13, 08:39 PM
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You really need to look for other things to worry about. There are 2 kinds of cured concrete--that which has already cracked, and that which is about to crack. Looking for foundation cracks with a magnifying glass and flashlight belongs in the same category as making sure all of your automobile trips contain the exact same number of right and left turns, to ensure that the tires wear evenly. You could plot each day's most efficient course on a map, just to make sure. Don't laugh--I knew a guy who did just that, to make sure his car's tires wore evenly.

Your photo shows far more than usual air entrapment in the foundation walls (air bubbles), caused by inadequate consolidation when the concrete was poured. It's not likely to ever cause problems, but if you ever tire of the crack monitoring thing, you could always measure and categorize all of the visible air bubbles.
 
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Old 01-30-13, 06:15 AM
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Bridgeman45...point well taken. I will endevour to inspect the foundation from a distance...in other words if i have to get down an all fours with my face 2 inches from the concrete...i am too close

Thank you all for your input(s)
 
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Old 02-08-13, 08:35 AM
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More info with pictures

I don't mean to beat this thread to death, but during my foundation inspection yesterday, I found some additional concerns regarding two of the small hairline cracks beginning at the top of my (poured concrete foundation wall) travelling vertically/meandering down approx 3 to 4 inches or so.


As reviewed, In 2009 entire foundation was documented (by me) with a digital camera.

Although I have some substantial cracks from settling, these are stable and have not moved. In fact I hired a structural engineer to inspect these cracks in 2009 before purchase, and the foundation was given a clean bill of health.

These hairline cracks in question ...(the ones that meander down from the top of the foundation) i think...are shrinkage cracks and have have been there all along, hwever two of these cracks appear more visible now and seem much more prevalent now in the colder temperatures.

in fact....


This winter, two cracks in question have seemed to "open" up and travel further down the wall. One in the front of the house one at the back (opposite ends of the house).

When I look at the documented pictures, (which were taken in the summer of 2009), you can see a weathered unmistakable crack that you can follow down about an inch or so...then it begins to fade out to a faint 'line' that corresponds to the now visible crack taken yesterday @ -22 celcuis.

Again, it is hard to tell if this crack picture in 2009 extends to the same length as the one taken yesterday, but with some picture enhancement on the 2009 photo, there is some evidence that a small defect might have been there. however it is very evident now and does not appear the same length as the summer time photo, or as per any previous inspections.

The cracks are uniform, no stepping, and can easily be missed with the naked eye. The top of the crack seems a bit weathered, but the bottom of the crack (which did not appear before) is very 'sharp' and faint. In fact if you continually rub the crack with your finger you pretty well "erase" it!

I Live in NS and the weather has been crazy this year....one day it is +10 and raining and the next it drops to -7. These cracks in question were found when the temperature was -22 degrees C. (remember the pics were taken in the summer time year 2009).

These cracks do not go below grade, (or do not appear to as they either disappear or are so faint you cannot see them).


My question is this....do cracks travel...or open up in these cold temperatures...and possibly will close back up in the summer?

Since a picture says a thousand words..

I have include two pictures of the same crack...one taken in 2009 at +18 degrees C, and the other taken yesterday at -22 degrees C.

The crack in 2009 has been copied twice...once in its raw format, (2009) and the other with a black traced line to identify how much of the crack I can see on the original 2009 picture and to better show it's location (for those who do not want to zoom in).

Also I have taken into account the lighting during the pic shoot for both dates, but to be honest I can never remember this crack being so visible before....even last winter during inspection. The same goes with the one at the front of the house...it is not a prevalent as this one and have therefore not included it.

Any insights are welcome....not sure if this is concern enough to hire a structrual engineer.

Nothing has moved inside the house, (no drywall cracks) and all the other stable cracks in the foundation (that can visibly been seen), look exactly the same as they did 4 years ago. (These cracks in question, although visible, are also uniform and are not stepped....just bit wider thats all).

Update....just realized how crappy these pictures came out....so you will have to take my word on the 2013 pic. because you can't zoom in ...at least i don't think you can. If you look at the 2009 one where I traced a black line, you can see the crack begin at the top and then appears to re-crack at around 1/2 inch from the end of the first...in actuallity it just 'meanders' and connects to the bottom half and continues down. In the 2009 photo, I have traced the black guide line as to what I see as a very very faint line on the 2009 photo.

In the 2013 pic, or looking at the crack directly, you can clearly see the crack continues to about 1 inch above the grade...so in other words it seems to go another inch or so.

Therefore, I will include a 2013(2) with a black guide line to show the crack as viewed in present time with the naked eye.

There
 
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Old 02-08-13, 09:09 AM
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It has simple explanation not worth the myopic analysis.

Concrete does shrink through it life, although the rate decreases with age so it can possibly preate some tensile stresses in the concrete that do not show up as cracks.

Concrete does expand and contract with temperature. It also transmits heat laterally, so the no "magic" red line around the interior of a basement as so many people think(especially in Canada for some reason). The soil does wonderfully moderate all temperatures.

Cracks are caused by stresses (shrinkage and temperature) in a wall. The stresses can combine and either moderate or make conditions more severe. The stresses are always there until they can combine to be high enough to cause a crack to occur or lengthen.

In your situation, the cracks where considered "dead" since they appeared to end somewhere in the wall. Cold weather causes contraction of concrete and the extreme cold (not cold here) shrinks the concrete and could add to any long term shrinkage stresses existing and increase the length of a cosmetic crack slightly.

Don't worry - Your house will not fall down, collapse or leak like a sieve, but if you look long and hard enough you can always find something small to worry about.

If you want to go further hire a testing company to take specially prepared cores of the concrete to be polished/ground for analysis by a professional to look at the sample with a high powered microscope. This is done frequently for research on a microscopic basis regarding chemical bonds between the cementing materials and aggregate in concrete for durability analysis.

Dick
 
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Old 02-08-13, 09:29 AM
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Thanks Concretemasonry.

So basically you are saying that these cracks are more than likely becoming visible now due to the expansion and contraction (cold weather). My concern is that they didn't appear for so many years and now...here they are.

Also...i never heard the term 'red line' with respect to the interior of a basement..what is this?
 
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Old 02-08-13, 09:56 AM
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Our pediatrician used to tell us: "If you wake up in the middle of the night and worry that your baby might be cold. Pull up your covers and go back to sleep. If your baby gets cold they will let you know, otherwise let them sleep."

I believe you need to put your foundation worries to bed. If your baby gets upset she will tell you (doors that stick, windows that bind, drywall that cracks) otherwise pull up the covers and go back to sleep.

I admire your desire to try and be proactive but I think you need to relax a little. All materials will expand and contract in temperature extremes. Did you have a bad foundation issue at a previous home?
 
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Old 02-08-13, 10:27 AM
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Sniper, I hear you loud and clear, however I do not have a baby to keep warm at nite, but have had situations in the past that have saved me tons of cash due to early detection. Maybe not relevant in this case however;

In this instance i am more curious than anything else. I know little about the properties of concrete besides the very basic, hence my reliance on the professionals like yourself. Why would something remain stable for 12 years then decide to crack?...or at the very least become visible now.

I think (hope) my question has been answered as I am going with cold weather expansion...(at least that was my interpretation from Concretemasonry's response).

Call me OCD or whatever, but it interests me why or how a crack would begin at the top of the foundation wall as opposed to coming up from the bottom (which it might) as I am assuming that the below grade is at least 4 feet under and I am only seeing the top 1 foot.

I suppose I should thank my lucky stars they are vertical and not horizontal....

I have many hairline cracks just like this one and none have moved except two. I am assuming that these would be classified as 'shrinkage cracks" again not sure, but they are the width of a pencil and only meander down a maximum of 6 inches (maybe 12 in some cases).
 
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Old 02-08-13, 11:21 AM
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Back to worrying about cracks again? Naughty boy.

So whatever happened to the concrete void documentation study I told you to undertake, for all of the entrapped air voids visible on the surface of your walls? Finished already? I must have missed it if you posted it here.

But returning to rational thought--yes, concrete does expand and contract with changes in temperature. The coefficient of expansion/contraction is 0.0000055 ft. per ft. per degree F. Meaning a 50' long wall will shrink a total of 0.0165 ft. (3/16") if the wall temperature drops 60 degrees F. You'll have to do the conversion for degrees C. Any existing cracks located in that same wall will open up a combined total of that same 3/16".

It's no mystery why you have wall cracks originating at the top, then meandering down vertically to nothing. When your house's foundation was poured, the fresh concrete at the top of the open forms was allowed to be exposed to the air and wind, instead of being properly cured (either covered with plastic, or sprayed with curing compound). This caused rapid loss of moisture by evaporation in the top foot or so of the mix, and resulted in shrinkage cracks because of strength loss in those areas. Very few residential contractors believe in good curing practices, unless specifically required by project specifications, which is highly unusual in residential work. The moisture required for proper hydration of Portland cement particles is instead lost to the air, with weaker and often cracked concrete the result.

Bottom line is, the cracks are there, don't worry about them, and go take care of your baby. If you insist on worrying about something, how about the impending collapse of the lovely Confederation Bridge over to Prince Edward Island? With rising sea levels, it's just a matter of time before crushing ice forces get higher than the level of the truncated pier column shafts (designed to deflect large ice floes)--now that would be something to worry about.
 

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Old 02-08-13, 12:13 PM
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@BridgeMan,

You actually answered my question with something that makes sense to me! Thank you!

I have seen poured foundations in the past an always wondered why some contractors put hay on top all around the foundation wall...I never new why but now i know!

Can't say whether or not they did that in my case...but probably not. Nonetheless this has answered my question about the cracks and your temperature vs. foundation length has answered why they (or some) have gotten bigger.

Thank you again
 
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Old 02-08-13, 01:26 PM
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Hay is sometimes used to prevent concrete from freezing (acting as an insulator, to keep the heat of hydration in), but it does very little to prevent curing moisture from escaping.
 
 

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