Cause of hairline crack on garage floor and exterior wall

2/4/2016 at 1:17:19 PM

Hi Martin,

It would not be possible to diagnose the cause of the cracks in a forum like this, however here is some information you might find useful.

Unless we are talking about a complete and catastrophic failure of the foundation, most cracks start out as hairline. Having said that, shrinkage cracks in concrete are fairly common and if that is in fact what you have it would not be cause for concern.

Here are some things to check to see if you should be concerned. Please note that "concern" is valid and is not an opinion. Follow these steps first and ignore "opinions" from others, especially anyone that has a vested interested in the result (i.e. The Builder may dismiss it and reassure you that it is nothing because they do not want to absorb the cost of the repair while a foundation contractor may state that it is a serious concern because they want the work). That is not to say that either would do that, but you are far better to eliminate the possibility.

1) Did these cracks appear recently?

2) Did these cracks appear at around the same time?

3) Are these cracks diagonal?

4) Do these cracks appear to start at the corner of a window, door, or basement post?

5) Is the concrete on either side of the crack on the same plane? (that is to say, if you put a straight edge against the wall or floor spanning the crack are both sides still in line or is one side higher than the other). Note that being in line with each other has nothing to do with level or plumb.

6) If they are on the same plane (#5 above), use a pencil and mark two lines (one on either side of the crack) and accurately measure the distance between the two. Write the date and the measurement on the wall at that location and monitor it about once a week and note any change.

If the cracks are diagonal and/or appear to be radiating from the corner of a window or door opening or on the floor at the base of a post or corner of a wall, or if the two sides of the crack are no longer co-planer, then you need to contact a Structural Engineer (P.Eng) and have them do a site visit and provide you with a stamped report. You can then use this to tender the repair work out to licensed contractors in your area.

If the cracks appear to be in the middle of a wall, both sides are in line with each other and are less than 1/8" across, did not suddenly appear recently, and are not opening or closing, then you are quite likely perfectly safe.

Please understand that this information is for you to use and make your own determination. I cannot advise you over this very useful forum.

If you have any doubts or concerns, do not hesitate to contact a Structural Engineer in your area. A report like the one I mentioned would likely cost only a few hundred dollars which in my opinion is the cheapest insurance you can get and provides great peace of mind for you and your family.

Best of luck,

Jason Irving

Cedarfalls Building Consultants Limited

2/4/2016 at 1:29:48 PM

Jason Irving, thank you for your very comprehensive reply!!! I will follow your advice.

Martin Ong