Cracks in Base­ment Walls — Why a Foun­da­tion Cracks

Jan 24, 2012 • By Matthew Stock.

Next time you’re in your base­ment, take a look around at your foun­da­tion walls. You are bound to find a crack. Why? Cracks in base­ments happen!

Builders approach us all the time to help them fix the foun­da­tions they just poured. It’s not that they do a bad job — it’s just the nature of the beast. 

Chica­go may be known as the Sec­ond City, but we are first in the num­ber of poured con­crete foun­da­tions in the coun­try. Hav­ing water­proofed over 300,000 base­ments and crawl­spaces since 1957, we’ve seen it all. I often joke around that we should be in the Gui­ness Book of World Records for repair­ing the great­est num­ber of foun­da­tion wall cracks.

Okay, so no one likes a brag­ger. But if you are read­ing this blog, and you want to have a bet­ter under­stand­ing of why cracks hap­pen, this should pro­vide you with a lit­tle insight. 

Rea­sons for Cracks in Base­ment Walls:

Stress Points

Any­time you core thru the wall for instal­la­tion of sew­er, elec­tric and gas lines, it weak­ens the con­crete, which can result in crack­ing. Cracks are also com­mon­ly found angling off cor­ners of base­ment win­dows. These areas are usu­al­ly the first place we look when con­duct­ing a foun­da­tion analysis.

Soil Sat­u­ra­tion

In sim­ple terms, soil sat­u­ra­tion = wet ground. Your base­ment walls are sup­port­ed by foot­ings. The foot­ings are at the base of the walls, and hold up your house. When the soil under the foot­ings becomes over­sat­u­rat­ed, the foot­ings ​“set­tle”, caus­ing the walls to crack. Over­sat­u­ra­tion can also cause the earth next to your foun­da­tion to expand in vol­ume. Many foun­da­tions aren’t built to with­stand that extra pres­sure. The excess weight of the soil can force the walls to push inward. This is iden­ti­fied by diag­o­nal cracks com­ing off cor­ners. The lead­ing caus­es for over­sat­u­ra­tion are improp­er grad­ing, bad gut­ters or the need for under­ground sump pump and down­spout exten­sions.

Drought

On the oth­er hand, not enough mois­ture in the soil can also cause foun­da­tion cracks. When the soil is des­ic­cat­ed, in oth­er words, when mois­ture is drawn from the soil, usu­al­ly as the result of a drought, the soil itself will shrink and cause foun­da­tion walls to shift out­ward and foot­ings to set­tle. Such soil des­ic­ca­tion occurs when trees, shrubs and oth­er plant­i­ngs near the foun­da­tion send root sys­tems deep­er into the ground in search of mois­ture, draw­ing it from the soil in areas that nor­mal­ly remain untouched.

Con­crete Shrinkage

Yes, George Con­stan­za — shrink­age! The sci­ence of pour­ing con­crete involves many fac­tors and vari­ables. Since water is used when con­crete is mixed, there is an inher­ent expan­sion and sub­se­quent con­trac­tion of the con­crete when it dries. Many fac­tors can affect the dry­ing process, includ­ing the type of aggre­gate, mix of the con­crete and humid­i­ty levels. 

Tim­ing

In life, tim­ing is every­thing. Same holds true for con­crete. Imag­ine your builder ran short on con­crete when pour­ing your foun­da­tion — and the next ready mix truck didn’t arrive until the first batch start­ed to hard­en. Your foun­da­tion would no longer be mono­lith­ic (one piece) at that point. A cold joint would nat­u­ral­ly form, allow­ing water to eas­i­ly seep through. 

Death and tax­es are two cer­tain­ties in life. Often, so is a cracked foun­da­tion. For­tu­nate­ly, the solu­tion is usu­al­ly very sim­ple, espe­cial­ly for a com­pa­ny that belongs in Guin­ness Book of World Records. 

Tags: foundation cracks, why cracks form, basement crack, cracks in basement walls

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