Foun­da­tion cracks can have many causes

Winnipeg Free Press - Section G - - RESALE HOMES - MIKE HOLMES

SO here’s a ques­tion for you, cour­tesy of dozens of emails: Dear Mike, I’ve got a crack in my foun­da­tion — is it a prob­lem?

Yes, ab­so­lutely. And, not nec­es­sar­ily. There are dif­fer­ent types of cracks, as well as dif­fer­ent types of foun­da­tions. And, depend­ing on where the crack is, it may or may not be a big deal.

I’m go­ing to say it up front: If you’ve no­ticed a crack in your base­ment floor or wall, you should call in a foun­da­tion spe­cial­ist for an opin­ion. You aren’t qual­i­fied to as­sess if it’s se­ri­ous, and I can’t see it from here. It may be a new crack, or it’s got big­ger so you’ve just seen it for the first time. Nei­ther of those is good news.

A lot of peo­ple are afraid of call­ing in spe­cial­ists be­cause they think it will cost more, or be­cause they think there will be an up­sell on the ser­vices re­quired. But this is not some­thing you should let slide, be­cause the crack won’t fix it­self.

In this case, what I don’t know can’t hurt me is 100 per cent wrong (like it usu­ally is). With a foun­da­tion crack, your house’s struc­ture could be com­pro­mised, and that is se­ri­ous. Here’s some things I do know:

Small cracks can in­di­cate big prob­lems.

Small cracks can let in­sects, ver­min and wa­ter in.

Small cracks can grow big­ger, and the big­ger the crack, the more ex­pen­sive the re­pair.

Dif­fer­ent cracks in­di­cate dif­fer­ent pos­si­ble prob­lems with your foun­da­tion, and they give clues to what the cause might be. Bulging and bow­ing walls, step cracks in blocks or bricks, ver­ti­cal cracks, hor­i­zon­tal cracks, in walls, in floors — they all mean some­thing. So what causes foun­da­tion cracks? The most com­mon cracks are caused by con­crete shrink­age. Con­crete is made with wa­ter, ce­ment and ag­gre­gate — it will shrink as it cures and dries. It is af­fected by tem­per­a­ture, both cold and hot. If its cur­ing is in­ter­rupted by a drop in tem­per­a­ture — let’s say an in­tense cold freeze hap­pens on the night your base­ment walls were poured — that will af­fect the fi­nal prod­uct. Or, if your base­ment pad was poured in in­tense heat and sun, it will dry too quickly. That will cause crack­ing.

Cracks caused by con­crete shrink­ing aren’t usu­ally a prob­lem — at least not one that’s struc­tural. But they can still al­low wa­ter or in­sects to get into your home, so they need to be dealt with.

An­other rea­son might be set­tle­ment; your house is set­tling into the soil. That’s not so good and it might be caused by a few rea­sons. For ex­am­ple, if your house’s foot­ings aren’t ad­e­quate or are dam­aged, there might be set­tle­ment, which can cause cracks.

This set­tle­ment might be caused by some­thing be­yond your con­trol. For ex­am­ple, if the soil around your home is sat­u­rated with wa­ter, or if your area has had a drought for a long time, you may find prob­lems de­velop with your foun­da­tion. In the first case, the ground­wa­ter rises and ex­erts pres­sure against your house’s foun­da­tion walls and floor. In the case of ex­tended dry pe­ri­ods, the soil ac­tu­ally shrinks as the wa­ter evap­o­rates out and that can al­low your foun­da­tion to set­tle. That set­tling may cause a part of your home to sink.

Con­crete has a lot of com­pres­sive strength but not much ten­sile strength, so it’s prone to crack­ing if there is lat­eral pres­sure push­ing against a wall. That’s why we add re­bar or fi­bre to con­crete in some sit­u­a­tions to im­prove its ten­sile strength.

So where is that pres­sure com­ing from? There is a lot of pres­sure in the soil. It’s from the wa­ter that’s held in the soil around your home, and in the wa­ter ta­ble. The amount of this wa­ter will change, depend­ing on sea­sonal rain and drought, es­pe­cially on clay soil.

Think about your house as a boat, ex­cept in­stead of float­ing in wa­ter, it’s sort of float­ing in the soil that sur­rounds the base­ment. That soil is fluid; it’s in mo­tion, and it’s shift­ing and ex­ert­ing pres­sure at all times on your foun­da­tion.

Some wet soils can be al­most 40 per cent wa­ter. So, think about ex­tremely dry con­di­tions, when that soil will shrink, and how that can af­fect your home. In times when there is too much rain­fall over a pro­longed pe­riod of time, what’s that wa­ter pres­sure go­ing to do? And, in win­ter when that wa­ter freezes, it will ex­pand, putting more pres­sure against the wall of your foun­da­tion. That can cause a crack.

There are lots of other rea­sons for cracks in foun­da­tions, some as sim­ple as back­fill­ing around a house dur­ing con­struc­tion. That can lead to crack­ing, ei­ther by equip­ment hit­ting the wall or dump­ing the load against the im­prop­erly sup­ported wall.

Not all cracks should be taken lightly. A hor­i­zon­tal crack is one I’d pay at­ten­tion to. Typ­i­cally they in­di­cate your wall’s struc­tural in­tegrity has been un­der­mined.

Hor­i­zon­tal crack­ing higher up on the wall is usu­ally from frost dam­age and the freeze-thaw cy­cle; wa­ter from your down­spouts or sump pump sat­u­rates the area, it freezes and ex­erts pres­sure on the base­ment wall. Or it might be from ve­hi­cle dam­age or im­proper back­fill.

Crack­ing fur­ther down the wall is more likely to be caused by the pres­sure of the earth it­self. This is es­pe­cially true on hill­sides and in ar­eas with wet, heavy soil. The force on your base­ment wall ex­erted by the soil is far greater at the bot­tom of the wall than at the sur­face. It might start as a crack but it will con­tinue to press in­ward and push the wall in, caus­ing se­vere struc­tural dam­age. It might even cause your base­ment wall to col­lapse in­ward.

When it comes to base­ment cracks, don’t be an ostrich and stick your head in the ground. If you’ve got a foun­da­tion crack, check it out. Call in a struc­tural en­gi­neer or foun­da­tion spe­cial­ist for an opin­ion.

— Postmedia News


Mike Holmes in­spects a crack in the base­ment. A crack in the foun­da­tion may be se­ri­ous, or not.

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