Crack in block basement wall

[13bob1313]

Hello. I have a pretty typical horizontal crack in the mortar of a cmu basement wall. Unfortunately, this is my own basement. I am a structural engineer, but don't have much experience in this area, and was hoping I could ask a few questions. Some info:

House was built in 1955. Low basement ceilings (<7 ft), and 12 inch block, so I'm assuming it is ungrouted. The crack is on a bearing wall (only 1 story).I have owned this house less than 2 years, and this appears to be a new crack. However, the wall was heavily painted, and it's possible the crack was always there and I just didn't notice it, and now the paint is peeling away.

The crack is consistent in size, only 0.03 inches running horizontally. It runs the middle length of the wall, and goes in a step pattern to the footing at each end. So it appears to be a pretty obvious case of an overloaded wall with tension cracks. The wall is deflecting about 0.5 inches at the crack. The soil around my house is mostly clay, too.

What I don't understand, is that the crack (and max deflection) is located in the upper third of the wall, actually at grade level. I should also mention the top three courses are 8 inch block, and the crack is in the mortar between the transition from 8" to 12". The area outside is covered by a deck, and i did some crawling around under there and it was really poorly graded. Strong possibility of standing water outside the wall.

Any thoughts or opinions would be greatly appreciated, especially on repair methods. I've seen these carbon fiber strips discussed, that seems to be the most economical. Or using steel members tied to the floor slab and to the floor joists. My thoughts are to monitor the crack, see if there is any change in size, before trying an expensive repair. The crack and deflection don't seem too horrible to me, at this point. Thanks

 

[oldestguy]

Is your climate in norther areas where frost occurs? A common effect from that is horizontal push mainly just below grade as main effect.

Things cn be done to hold it, if necessary, such as bracing inside and insulation below grade outside among other things.

 

[13bob1313]

yes, I do live north, in Michigan. Freeze/thaw was my other thought, being that the crack appeared in the spring...The wall has been through many cycles though, so I would think this crack was likely pre-existing and just covered by paint if that were the case? Do you think a fix is necessary given the size of the crack and deflection? Thanks

 

[TehMightyEngineer]

I have a similar wall on my house with similar climate (Maine), similar 1960s construction (block wall, mine appears to be grouted though), and it also has a horizontal crack that follows the edges of the block at mid-height. However, it has been confirmed by the prior owners to be there for a long period of time. I bought it only last year so I've only been monitoring it accurately for that time. I wouldn't be very concerned about it, I'd monitor for movement and regularly check in throughout the year to see if it's just frost expansion or swelling soil during the wet months. I plan to finish my basement and will epoxy inject the crack prior to that just to prevent any moisture from getting in.

The two main cracks are approximately 0.060" and 0.043".

Since you can't epoxy inject your wall, perhaps you could grout a few cores by demolishing a grout hole in a select few blocks and filling the cores with a low slump grout. You could then sawcut the crack to a nice profile and apply an appropriate elastomeric sealant. Should both prevent further movement, reinforce the wall, and seal the crack nicely.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[XR250]

I would monitor it for further movement. As long as the top of the wall is braced properly (i.e. joists perp. and anchor bolts exist), carbon fiber strips are the way to go IMHO. Soldier beams would be the second option. I do not agree with Ted's repair methodology unless you could get some full-height rebar in there.

 

[oldestguy]

I'd also monitor. However, I'd caution doing any finishing that covers or insulates against cold. Currently the loss of heat to the outside tends to minimize pushing by frost out there.

Any outside work that will insulate or reduce water infiltration may help, but only major work will eliminate it.

 

[13bob1313]

Thanks for the replies, relaxed my mind a bit on this.
I'll monitor it for now, and fix the grade under the deck. Hopefully if I keep the water away, i won't see any more movement in the wall. Should be fun!

 

[focuseng]

Monitor for movement. 1/2" out of plane deflection is not at high risk and you have approx 60 years of history here. Tape or fasten some type of measuring stick on each side of the crack and mark the alignment and date. Remember some tape will deteriorate and you may have this here for decades. Do this in a few locations Keep track seasonally and with rain events. The two solutions you describe are most common. There should be a plethora of "foundation repair" specialist within your area to get some quotes on if you want them. I think the steel column/beam option is the most used repair because it is easy, readily fabricated, and not to expensive. The fiber tape should be installed by someone trained and very experienced.

______________
MAP

 

[oldestguy]

crack width measurement is easily handled by this method:

Draw a line across it about 3 inches long. Place 2 cross mark on each side, two inches apart.

Periodically measure this distance and any misalignment of the line or wall horizontal difference (top in or out from bottom)

 

[SLTA]

What oldestguy said, or buy a crack monitor and epoxy it across the crack.

Please remember: we're not all guys!

 

[13bob1313]

Thanks guys/gals. Ya I just used one of those cards with different line widths, but agree, I'll need a more precise method as you two described.

My concern with the steel option is potential future buyers would be put off by seeing that, the fibers are more discreet. But hopefully I don't have to go there. Thanks again everyone.

 

[BS2]

I see this condition all of the time in my neck of the woods. I typically allow up to 3/4" of movement before I recommend reinforcing. If the movement is larger than this, I typically recommend vertical wall restraints (small S shapes or HSS's) embedded in the slab, connected to the floor joists, and spaced at 4' on center for CMU walls. Cost is approximately $250 - $350 per restraint, installed.

 

[Tmoose]

Pictures are always nice.

 

[StrucPatholgst]

Horizontal cracks at grade are usually frost heave cracks. If it were moisture-laden soil, the crack would most likely have presented itself at a point of maximum stress, which for a vertical wall is 2/3's the way down from grade towards the slab. I use Day's book when assessing cracks, which is to say I never use just one feature (such as crack width) to assess damage and degree of repair. I look for displacement, rotation, leaning, bulging, crack location, crack width, and crack frequency, then I make a judgement call on where the damage falls across 5 categories (Very slight, Slight, Moderate, Severe, Very Severe). Then I make a repair recommendation, and back up my conclusions in the report with my measurements and observations.

 

[13bob1313]

strucpatholgst, what's Day's book?

 

[StrucPatholgst]

http://www.amazon.com/Forensic-Geot...words=geotechnical+and+foundation+engineering

 

[chicopee]

As I was reading all the replies, there was no statement about storm water( rain storms and melting snow) getting into the cracks and whether such situation should be a concern. Personally, I would take the extra effort and seal up said cracks from the outside.

 

[SLTA]

13bob1313, could be this one: Day's Forensic Geotechnical and Foundation Engineering, 2nd Ed

(referenced in this thread, 4th post)

Please remember: we're not all guys!

 

[SLTA]

And duh to me. read all the responses before answering.

Please remember: we're not all guys!

 

[TehMightyEngineer]

chicopee: Regarding the water, if there is no penetration into the basement (likely obvious with some effervescence) and as he has no rebar I would think there's not much serviceability issues with cracking on the outside, except perhaps the blocks excessively wicking up moisture into the framing.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com