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Foundation cracks guide

Posted Mar 31, 2021 in Foundation Crack Repair, Waterproofing

Find­ing a crack in your base­ment wall or floor can be dis­heart­en­ing and cause great anx­i­ety. Imme­di­ate­ly you start wor­ry­ing about dam­ag­ing water flood­ing the space and the cost of repairs. You can hire a pro­fes­sion­al to inspect it, but then you’re con­cerned about major reme­di­a­tion work he might rec­om­mend. How will you know when to start worrying?

This com­pre­hen­sive guide to foun­da­tion cracks will pro­vide a con­cise syn­op­sis of every type of crack that may plague your base­ment, the pos­si­ble caus­es and what type of work will be nec­es­sary to cor­rect it. There are many types of foun­da­tion cracks that can occur, sig­nal­ing some type of dam­age, but repair work will vary based on the type of foun­da­tion mate­r­i­al plus the size, shape, and loca­tion of the crack. It’s impor­tant to accu­rate­ly deter­mine the size of the crack. Mea­sur­ing with a tape or ruler can be dif­fi­cult for any­thing less than 1÷4”. An easy ref­er­ence is: 1÷32” = width of a cred­it card, 1÷16” = width of a nick­el, 1÷8” = width of two nickels.

Now you’re ready to inspect and eval­u­ate your own foun­da­tion to deter­mine the best course of action.

Wall shrink­age foun­da­tion cracks

You’ll notice these are gen­er­al­ly uni­form in width or some­times, less com­mon­ly, appear as V‑shaped cracks. These will be wider at the top and get small­er as they trav­el ver­ti­cal­ly down the wall. They will range in length and will stop before reach­ing the bot­tom of the wall. Shrink­age cracks will appear under base­ment win­dows, above doors, at step-down areas and in the cen­ter of a long wall if con­trol joints were not used. They’ll usu­al­ly be less than 1/16-inch wide and show up as hair­line, spo­radic, ran­dom, and dis­con­tin­u­ous cracks or a com­bi­na­tion of all types in the wall. Shrink­age cracks almost always extend through the full depth of the foun­da­tion wall so maybe a source of water entry.

Caus­es of wall shrink­age cracks

Shrink­age occurs as con­crete cures, which is a chem­i­cal reac­tion and affect­ed by the amount of water, aggre­gate type, humid­i­ty, ground­wa­ter, sun expo­sure, tem­per­a­tures, and oth­er con­di­tions. These cracks can be caused at orig­i­nal con­struc­tion due to sev­er­al fac­tors, depend­ing on the type of con­struc­tion. As con­crete shrink­age occurs, it will devel­op inter­nal stress­es. Crack­ing relieves this stress dur­ing curing.

Poured con­crete foun­da­tion walls –

Shrink­age cracks can be caused by poor mix, rapid cur­ing, improp­er or omit­ted steel rein­force­ment. Tem­per­a­ture swings con­sis­tent with the change of sea­son can also cause the con­crete to expand or con­tract to cause cracking.

Block foun­da­tion walls –

Shrink­age cracks are gen­er­al­ly uni­form in width, form at the cen­ter of the wall and are also caused by cur­ing and tem­per­a­ture variations.

Brick walls –

While bricks are no longer used for present-day foun­da­tions, old­er build­ings may still have struc­tur­al brick walls in place to sup­port the first floor. Brick walls don’t nor­mal­ly shrink but expand forever.

Repairs of wall shrink­age cracks

Shrink­age cracks usu­al­ly don’t require any reme­di­a­tion work or struc­tur­al mon­i­tor­ing in poured or block walls. You can expect to see more as the foun­da­tion dries com­plete­ly. How­ev­er, brick wall cracks will not be caused by shrink­age and may indi­cate a struc­tur­al or sup­port prob­lem. Cau­tion should be used if the bond cours­es are bro­ken. There is a sig­nif­i­cant risk of wall col­lapse, so con­tact a pro­fes­sion­al immediately.

Shrink­age cracks can be sealed to pre­vent water entry by chip­ping out the crack, fill­ing with mason­ry patch­ing com­pound, epoxy, polyurethane foam or oth­er sealants.

Wall set­tling cracks

Ver­ti­cal Wall Cracks

These are often present in poured walls, wider at the bot­tom and con­tin­ue to increase in length and width. These will like­ly occur short­ly after con­struc­tion, extend down the entire length of the wall to the floor and pos­si­bly be the site of water infil­tra­tion. Set­tling cracks can increase in size to ¹⁄₄″ or more or stop completely.

Caus­es of Wall Set­tling Cracks

These are caused by foun­da­tion move­ment due to poor­ly pre­pared foun­da­tion foot­ings, improp­er­ly placed or omit­ted steel rein­force­ment. Hydro­sta­t­ic pres­sure from the sub-grade set­tle­ment, hor­i­zon­tal load­ing from the struc­ture above and back­fill­ing can also cause uneven stress­es and lead to crack­ing. Hydro­sta­t­ic pres­sure exerts force against the exte­ri­or foun­da­tion wall and becomes more severe fur­ther underground.

Diag­o­nal Wall Cracks

While the major­i­ty of set­tling cracks dis­play ver­ti­cal­ly, diag­o­nal cracks may arise at a cor­ner of a con­crete wall where it was exposed to frost dam­age, expan­sive clay soil, point loads exceed the con­crete mix used, or even a tree/​shrub plant­ed too close to the foun­da­tion wall. A diag­o­nal crack under a ground floor win­dow can be due to foun­da­tion heave indica­tive of shal­low or absent foot­ings. Cracks that appear any­where else on the wall that are wider at the bot­tom than the top will indi­cate set­tle­ment under the building.

Hor­i­zon­tal Wall Cracks:

These often show up in con­crete block con­struc­tion, and where they appear will deter­mine the cause and sever­i­ty. If they are locat­ed in the upper third of the block wall, they were like­ly caused by sur­face and sub­sur­face frost or vehi­cle loading.

Mid-wall height cracks:

Are like­ly from dam­age by use of heavy equip­ment near the wall, pre­ma­ture or exces­sive back­fill­ing before the floor fram­ing was set, or earth load­ing wors­ened by water or frost.

Low-wall height cracks:

Are usu­al­ly caused by earth load­ing and exac­er­bat­ed in areas of wet or dense soil. Earth pres­sure is the strongest at the bot­tom of the wall and may dete­ri­o­rate as the hor­i­zon­tal move­ment at the wall is pushed inwards.

Block or brick walls will crack straight along a joint or stepped near the ends of the wall. This, too, can be extreme­ly dan­ger­ous and risk col­lapse if wall cours­es are bro­ken. In all cas­es, cracks will appear in mul­ti­ples in var­i­ous loca­tions around the foun­da­tion. 16″ to 48″ from the top of the wall and run par­al­lel to the floor.

Repairs of wall set­tling cracks

Ground con­di­tions and the mate­r­i­al will dic­tate the type of repairs that are rec­om­mend­ed to cor­rect set­tling issues. The foun­da­tion must be sta­bi­lized and dri­ven steel pins are one method of accom­plish­ing this. Pins are dri­ven into the soil next to the foun­da­tion and seat­ed on bedrock.

Short­er heli­cal screw piers or fric­tion piers can be used to pre­vent fur­ther set­tle­ment where there is no oth­er sup­port. Unsta­ble soil con­di­tions will war­rant the use of rod and chan­nel repairs. Thread­ed steel rods attach the dam­aged foun­da­tion to steel U‑channels outside.

Exca­va­tion and recon­struc­tion may be nec­es­sary for exten­sive repairs. This type of work is gen­er­al­ly com­bined with base­ment water­proof­ing and drainage com­po­nents to pre­vent a recur­rence of the prob­lem. This may include cor­rect­ing roof or sur­face runoff prob­lems or installing a French drain sys­tem. Severe set­tling cracks should nev­er be sealed with caulk or epoxy with­out com­plet­ing the nec­es­sary repairs.

Floor shrink­age and set­tle­ment cracks

There are three dif­fer­ent meth­ods of installing poured con­crete floors and each has unique char­ac­ter­is­tics and rea­sons for cracking:

1. Float­ing slab –

Con­crete is poured over lev­el loose-fill dirt or grav­el. As the soil is not gen­er­al­ly com­pact­ed, there is a risk of crack­ing and set­tle­ment. Water runoff, flood­ing or leaks can seep under the build­ing and cause set­tling. Any vis­i­ble foun­da­tion cracks, how­ev­er, will not affect the over­all struc­tur­al sound­ness of the building.

2. Sup­port­ed slab –

In this case, the edges of the floor rest on a lip in the con­crete foot­ing. The soil and grav­el base are com­pact­ed. Soil set­tle­ment will have lit­tle effect on this type of pour as long as it has been rein­forced; how­ev­er, sig­nif­i­cant set­tling or improp­er rein­force­ment at pour can result in total collapse.

3. Slab on grade –

This method is used when a mono­lith­ic slab and the build­ing foot­ers are poured at the same time. Cracks may be indica­tive of foot­ing set­tle­ment and maybe a struc­tur­al concern.

Repairs of floor shrink­age and set­tle­ment cracks

Shrink­age cracks in the base­ment con­crete floor are com­mon and rarely indi­cate the cause for con­cern. How­ev­er, there are some reme­di­al meth­ods avail­able to slow fur­ther cracking:

Adding con­trol joints, if not includ­ed in the orig­i­nal con­struc­tion, can reduce the stress of shrink­age. While cracks may still appear, they’ll like­ly be locat­ed with­in the joints and not across the floor.

Non-struc­tur­al cracks that are allow­ing water infil­tra­tion can be sealed with polyurethane foam injec­tion. This will stop leaks and can be smoothed over and cov­ered with a con­crete seal­er or paint to cam­ou­flage unsight­ly cracks.

It’s high­ly rec­om­mend­ed repair­ing the floor slab set­tle­ment when cracks exceed ³⁄₁₆″ in width or ¹⁄₈″ ver­ti­cal dis­place­ment. Slab-on-grade instal­la­tions rec­om­mend repairs for cracks in excess of ¹⁄₁₆″ in width or ver­ti­cal dis­place­ment. Trip­ping haz­ards, even though no struc­tur­al con­cerns are evi­dent, should also be repaired. Sev­er­al meth­ods can be imple­ment­ed and are described as follows:

Mud jack­ing –

This process is used to lift the con­crete floor slab by pump­ing low-strength con­crete (mud) under­neath. Polyurethane resins can also be inject­ed under the foun­da­tion. The com­bi­na­tion of resins solid­i­fies into plas­tic that con­tains gas bub­bles. As it expands, the floor will be raised. This method is suit­able as long as load-bear­ing rock or sta­ble soils aren’t too deep.

Grout Pumping/​Slab Jacking –

This method is used to raise inte­ri­or con­crete slabs on grade, mono­lith­ic con­crete slabs or fill voids under­neath the floor where bedrock or sta­ble soils are deep. Thixotrop­ic grout is inject­ed under pres­sure to fill the void below the slab.

French Drain System –

When it’s deter­mined that ground­wa­ter is flow­ing under­neath the floor and erod­ing the soils away, a French drain sys­tem can be installed. A trench is cut around the inte­ri­or perime­ter of the base­ment where a PVC drain pipe is installed in grav­el and con­nect­ed to a sump pump to car­ry excess water safe­ly away from the home.

Some repairs will require exca­va­tion work which will entail the use of heavy equip­ment and expos­ing the foun­da­tion wall. While this will allow for a thor­ough inspec­tion of the foot­ings, walls, mem­brane and weep­ing tile, this is extreme­ly dan­ger­ous and should be han­dled by a pro­fes­sion­al water­proof­ing com­pa­ny or con­trac­tor. Floor crack­ing can be symp­to­matic of a larg­er set­tling issue, and this extreme process may be the only recourse in fix­ing the problem.

Iden­ti­fy action needed

Con­crete wall and floor cracks should be sep­a­rat­ed into three categories:

1. Cos­met­ic, requir­ing no fur­ther repair;
2. Mon­i­tor­ing need­ed, watch­ing for changes or wors­en­ing con­di­tions; and
3. Sig­nif­i­cant, def­i­nite­ly requir­ing repairs.

For those cracks, you’ve iden­ti­fied as need­ing repair, sep­a­rate those in order of pri­or­i­ty. Obvi­ous­ly, the most urgent are areas where there is a risk of col­lapse or unsafe con­di­tions. For those less urgent spots, make sure to sched­ule reme­di­al work in a short time frame as they will like­ly dete­ri­o­rate quick­ly. A pro­fes­sion­al inspec­tion should help in deter­min­ing poten­tial dam­age to the build­ing and the tim­ing of each repair.

By tak­ing a proac­tive approach to struc­tur­al changes, includ­ing con­crete wall and floor cracks, you may be able to avoid major repair work. Remem­ber, any time you have ques­tions or con­cerns about foun­da­tion cracks or water­proof­ing con­cerns, con­tact the experts at Fam­i­ly­Wa­ter­proof­ing Solu­tions for more infor­ma­tion (708) 330‑4466.