Foundation Cracks: Water Problem vs. Structural Problem


Foundation Cracks: Water Problem vs. Structural Problem

OK, so you’re in the basement one morning to dig a pair of clean socks out of the dryer.  Heading back upstairs you have one of those “wait a minute…” moments and think, “Did I see a crack in the wall?”  It bugs you all day at work so that evening you grab a flashlight and go down to the basement to investigate.

Poking around in the vicinity of the washer and dryer you spot it, a crack in your poured concrete foundation wall that wasn’t there the last time you looked, at least as far as you can remember.  Now that you’ve confirmed you weren’t seeing things that morning, what do you do now?  Call somebody?  Panic?  Ignore it?

Maybe you ask a question of no one in particular: “Is this a problem?”  Here’s the answer: “Probably yes.”  The more important questions to be asked are “What kind of problem?” and “How serious?”  The answers to these all lie, as they say in sports, in a “tale of the tape.”

Water Problem vs. Structural Problem

There are two kinds of cracks that occur in poured concrete foundation walls – cracks that affect the structure of the foundation and those that don’t but can still admit water.  Determining which is which is done by measuring the width of the crack and examining where on the wall it occurs.

Although it’s not an exact standard, a good rule of thumb is that a crack that is narrower than 1/8” is probably not a structural crack.  These non-structural cracks occur all the time, caused by minor settling or foundation movement or by lateral pressure from saturated soil.  They will typically be in the lower part of the wall, usually reaching to the floor.  They may be dry when first observed but, if they extend all the way through the wall, will seep water when ground water is high.

Structural cracks, on the other hand, tend to be wider than 1/8” and can occur at various points in the wall but typically are in the upper corners and in the middle.  These cracks generally appear in a roughly symmetrical pattern – if one corner is cracked, the other probably is too – and will contribute to ongoing movement of the wall, rotating in from the top and tipping off plumb into the basement space.

Structural vs. Non-structural Crack Repair

Repairing a non-structural crack is pretty easy and relatively inexpensive but requires the services of a waterproofing professional.  The technician cleans out the crack and inserts a number of plastic injection ports along its length.  He then applies a surface coat of fast-drying epoxy to cover the crack and hold the ports in place.  One the epoxy has cured, he injects each spot with expanding polyurethane, which fills and seals the crack all the way to the outside soil while remaining flexible when cured to prevent re-opening of the crack from minor foundation movement.

After the polyurethane has cured, the ports and epoxy can be scraped off the wall.

Fixing a structural crack is a somewhat bigger job.  If the damage is spotted before the wall has moved significantly (less than 2”) it can be repaired with carbon fiber strips.  Proper placement is determined by engineering data and the wall is ground smooth in spots where the carbon fiber is to be applied.  Technicians apply a coat of industrial epoxy and embed 12”-wide woven strips of carbon fiber in the epoxy, floor to ceiling, using a roller to ensure a complete bond.  A steel brace is then installed across the top of each strip between floor joists and the wall is completely stabilized against further movement.

If the wall has moved or rotated more than 2”, steel must be used to stabilize the wall.  A technologically up-to-date contractor will use channel steel, a low-profile beam instead of the old 4” or 6” I-beams of the past.  Channel steel is affixed to the foundation footings and to a brace between floor joists at the top the wall and can conform to the position and shape of the wall to ensure no further movement.

Either technique offers a low profile that can be completely hidden by a normal 2x4 stud wall.  Carbon fiber is so low-profile that it nearly disappears under a coat of paint alone.

Regardless if a foundation wall crack is structural or not, the homeowner who discovers one needs the help of a professional.  At U.S. Waterproofing, our experts in both waterproofing and foundation repair offer a professional diagnosis and appropriate repairs based on more than 50 years’ experience and technical expertise.  Why not ask for a free consultation?


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