A couple of years ago, my husband excavated outside our one below-grade basement wall (block) to install foundation drain and "paint on" and membrane and foam board waterproofing (sorry - I don't know the correct terms!). We live in North Georgia, in a "driveunder"/daylight basement ranch built very badly in the late 1970's.

Now, he's finally getting around to noticing the horizontal crack in that block wall that I warned him about 2 years ago (sorry, but I couldn't resist - why do husbands never think their wives know anything about construction?). He's had 3 different foundation/waterproofing companies out for estimates on making sure that wall stays put. Two recommended either carbon fiber straps OR steel beam reinforcement; the last is recommending wall anchors.

The last company is claiming that we have a "block ON TOP OF slab" wall -- which, considering the quality of the home builders in my area, is completely possible. But I wonder why the first 2 companies didn't mention it, and I (unfortunately, due to past experience) cannot trust my husband to confirm this -- so how can I confirm it? Can you tell just by looking? And does that change the recommended method of reinforcing a block foundation wall?

I oftentimes see people recommending that homeowners hire a "professional:" a structural engineer to consult and make recommendations. How does a lower-middle-class homeowner FIND such an engineer? Do I want a structural, or civil, or foundation, or geotechnical engineer?

thanks for any advice!

Well, all the people who made recommendations to you have one very important thing in common: NONE of them have made any attempt to discover the cause of the problem!! Do you expect your pharmacist to supply medicine without knowing what disease you have? I don't think so.

Carbon fiber straps and steel beams and wall anchors are all simply Band-Aids!. They do not do a thing about whatever is causing your wall cracks. Here are the primary causes of cracked foundation walls:
1. Hydrostatic (water) pressure outside the wall.
2. Soil pressure outside the wall.
3. Insuficient block thickness and/or reinforcing for the depth of soil outside the wall.
4. Incorrecr block type
5. Heavy equipment running too close outside the wall.
6. Improper backfill outside the wall (rocks, boulders, construction debris, etc.)
7. Tree roots outside the wall.

Did you notice a pattern to the above list? Yes indeed, six out of the seven common causes are conditions which exist outside the wall, and that is where the problem must be diagnosed and solved, NOT INSIDE!

Some questions: (which those contractors should have not only asked but also answered)
1. Which wall has the horizontal crack...the one that is completely or almost completely underground? (I'll bet I know the answer already, but answer it anyway)
2. How high is the cracked wall?
3. If you know, how much earth is there between the basement floor and grade outside?
4. How thick is the cracked wall, if you know?
5. Is the wall bowing at all? (you can tell by placing a straightedge with its center on the crack...if the straightedge rocks, the wall is bowed)
6. Has the base of the wall apparently moved on the floor slab? (if in fact the wall is built atop the floor slab)
7. What type of soil lies behind the wall?

With answers to these questions, perhaps we can narrow down the possible causes, or at least determine the seriousness of the problem.

Any good architect or structural engineer can advise you. The trick is finding the good ones. Even a good foundation contractor would be a good source. Any or all of them should begin by asking the same questions that I have asked, and should then try to help you determine the answers. Once the answers to those questions are known, the possible causes can be narrowed down by ruling some out. Then perhaps some simple excavation will be necessary to check on the rest of them.

Once you are CERTAIN of the cause, a solution can be selected.

quote:

1. Which wall has the horizontal crack...the one that is completely or almost completely underground? (I'll bet I know the answer already, but answer it anyway)

You got it -- the one that is essentially completely underground.

quote:

2. How high is the cracked wall?

Sorry -- whatever standard height is? 7'? 8? (I gotta get my husband to answer these questions!)

quote:

3. If you know, how much earth is there between the basement floor and grade outside?

Not sure what you're asking here but, if I understand, the top of the earth outside the wall slopes from top of the wall to maybe half-height of the wall.

quote:

4. How thick is the cracked wall, if you know?

Not sure again, sorry. Standard cement block width?

quote:

5. Is the wall bowing at all? (you can tell by placing a straightedge with its center on the crack...if the straightedge rocks, the wall is bowed)

Only minutely. I first noticed the crack 2 years ago -- a straightedge now rocks, across the crack, only fractions of an inch.

quote:

6. Has the base of the wall apparently moved on the floor slab? (if in fact the wall is built atop the floor slab)

Hmmm... How can I tell this? Gawd, I hope not!

quote:

7. What type of soil lies behind the wall?

Clay. We're in Georgia. There is, however, a couple of feet of sand/gravel fill over/under the french drain just below the slab, then clay backfill.

If I need to be more precise in these answers, I'll gladly get the answers. I just wanted to get my thoughts down asap on these questions.

I really don't know where to BEGIN to find a structural engineer (which is the expert I'd prefer to consult, as I know there are many forces at work, here).

Surprisingly, the one company did that look around is the one I trusted the least (due to reputation). This is why I really want a disinterested opinion.

Thanks

Where in the wall is the horizontal crack?

Lower 1/3? About the center 1/3? Upper 1/3?

That will tell what the cause may be.

****

It's about halfway up the wall, actually -- maybe slightly higher than halfway.

The concern today (as we're finally getting rain after our severe drought here in Georgia) is - does RAIN infiltration into the soil outside the wall put us at higher risk? Or is it more likely that this kind of pressure would come from, say, DRIVING up the front yard (which we've done) than from rain/soil settlement?

These kinds of questions are why I'm really confused about who I need to get to look at this. Would a structural engineer consider the impact of drought and/or rainfall on this wall?

Without knowing the rest of the answers, a prime suspect has emerged, and possibly two.

The primary suspect is the presence of clay directly outside the wall. The combination of clay soil plus water equals hydrostatic pressure, and this may be the cause of the crack and slight bowing.

The second suspect is a vehicle driven near the wall. How heavy a vehicle was driven near the wall?

These two suspects alone might not have cracked the wall, but perhaps the combination of the two was enough.

Count the number of blocks from the basement floor to the top of the wall, and multiply by eight inches, and you'll have the height of the wall.

Determining the wall thickness isn't as easy. Maybe you can get a clue at the top of the wall. Standard block thicknesses are 6, 8, 10 and 12 inches. The wall isn't likely to be six inches thick, and probably shouldn't be eight inches thick, but could be, and may be ten or twelve inches thick. If you can get up top and measure from the inside face of the wall to the rim joist (which runs continuously along the outer edge of the wall) and add an inch-and-a-half to that, you'll have a close approximation of the wall thickness.

The other dimension that would help is the distance from the basement floor up to the top of the soil outside the wall. You can get this by measuring from the bottom of your siding down to the finished grade, and subtracting that dimension from the total height of the basement wall that you got by counting the blocks inside.

One other question: what is the direction of the floor joists relative to the cracked wall: are they parallel to it, or perpendicular to it?

Still too early to be selecting a remedy, but it's looking like excavating outside the wall down to the gravel that is surrounding the drain pipe, and backfilling up to within six or eight inches of finished grade with pea gravel, for a width of twelve to eighteen inches. This will relieve hydrostatic pressure on the wall, and give you the opportunity to waterproof the wall so that you won't get water entering through the crack. If the bowing is minor, it can be ignored.

For a structural engineer, try the yellow pages under Engineers-Structural, or Engineers-Consulting. If you are in a small town, you may have to look in the nearest large city's yellow pages.

quote:

Did you notice a pattern to the above list? Yes indeed, six out of the seven common causes are conditions which exist outside the wall, and that is where the problem must be diagnosed and solved, NOT INSIDE!

Richard- Your method of posting made me laugh!

It is almost as I was reading LicensedWaterproofR

Happy Holidays!

I have noticed the same consistant situation.

In this case, the failure is a classic structural situation where the crack from flexure is at or just above the center of the wall (usually due to the partial fixity of the base of the wall). It is not a shear crack at that location.

The direction of the joists could be perpendicular to the wall since there is horizontal restraint of the wall by the floor system. The same condition can exist on a foundation wall parallel to the joists IF the joists are blocked/braced properly (which is not always the case on parallel joists).

It will take an engineer to determine the proper remedy. The wall as it sits now, is much weaker than it was when first was built and subesequently failed. It is doubtful if just changing out the backfill will be adequate without reinforcement (steel, grout and rebar) unless it can be shown that the moisture in the soil, which is the cause of high soil pressures can be eliminated. Just slopping on a waterproofing system (film, bonding material/selaer, etc.) does nothing but help keep the water out.

In 45 years, I have never seen it make a wall strong enough or stronger than the original. My name is also Richard, but I use my nick-name.

We don't have a solution yet, but gravel backfill will allow ground water to dissipate without causing hydrostatic pressure, and also allow water to flow down to the drain at the bottom of the wall, which it now cannot do because of the clay. If the bowing of the wall is minute, it can be ignored, provided it is determined that the wall thickness is sufficient fro the height of soil retained. The fatsre the hydrostatic pressure is relieved, the better the chances of saving the wall without further reinforcement. We still need answers to several other questions, and we do still need an opinion by a qualified professional who has examined the building and site and all conditions. All we can hope to do here is possibly narrow down both cause and possible solution.