How to address cracked foundation walls? (And does carbon fiber work?)

January 25, 2017 12:42 PM

There are a lot of companies that sell or install carbon fiber straps to repair or reinforce failing foundation walls. Those companies say this new way of reinforcing walls is basically the best thing since sliced bread (a few examples: 1, 2, 3). On the other hand, googling around, there's a persistent minority counter-opinion that these are ineffective, and little better than snake oil (examples: 1, 2). I'm curious what you think.

In my own situation (mid-50s concrete block foundation developing horizontal cracks in the walls), I've consulted several companies to get estimates and evaluations for addressing the problem (all reputable companies, in business for decades, with good Angie's List ratings, etc.) Half of them have prescribed the carbon fiber strap solution, the other half have proposed installing steel I-beam supports -- or building additional interior concrete walls -- while commenting that "that carbon fiber stuff doesn't and can't work."

I'm curious about two perspectives on this situation:

- If you're a homeowner who had to deal with the same situation, what did you opt for as a solution? Did you run into any problems (either up front or down the road)?

- If you're a contractor or an engineer, what do you think of the pros and cons of these different solutions?

posted by orthicon halo to Home & Garden (9 answers total)

No direct experience with these, but it might help to understand that the carbon fiber straps by themselves will be quite flexible, but should be good at resisting elongation. They can only work by preventing cracks from opening further than they already have, and they can only do that if they are extremely well adhered to the wall with rigid adhesive. If there's any problem with the bond, due to a fault in the adhesive or in the surface of the wall, then it can't work.
posted by jon1270 at 1:17 PM on January 25, 2017

(Note that in your third link, with the truck parked on a row of suspended concrete blocks, the strap across the bottom is doing all the work. The carbon fiber visible on top in that picture is pointless.)
posted by jon1270 at 1:20 PM on January 25, 2017

We ended up going with interior strapping over any of the exterior options in our house because we factored what the full outside repair would be over the likely lifetime of our house (a 1950's fixer upper bungalow on a street full of super nice infill houses).

To get our house fixed with exterior excavation was quoted to us at close to $80,000 and strapping was $7,500 with a 25-year transferrable warranty that it would never get worse. For us that was a no-brainer. Yes, the exterior repair might make the foundation perfect and indestructible forever, but we'd never get that money back out of the property. The $7,500 fix makes our house completely liveable, we can pass the warranty on to the new owner if we ever sell, and the house isn't falling apart anymore.

We've had the strapping for over a year now with zero issues with expansion. They also drilled into the wall all over and injected stuff into the cracks to make it completely waterproof and uncracked, I think that made a big difference as well. One thing our contractor took a lot of time explaining to us is the strapping/injections can't fix a problem (like if your floor is starting to slant because the basement wall has sagged), BUT they can make it so the problem doesn't ever get worse.
posted by Sweetchrysanthemum at 2:17 PM on January 25, 2017

Get a professional engineer to look at it... the foundation repair companies are pretty sketchy....
posted by miyabo at 4:13 PM on January 25, 2017

I'm not a homeowner or any sort of relevant engineer, but wanted to mention that if you Google for pillar earthquake "carbon fiber" you can see that enveloping concrete in carbon fiber seems to be a technique that's been used for a few decades for earthquake remediation. (If I recall correctly from a documentary I saw, the concrete structure is still effectively destroyed and rendered useless by the earthquake, but is less likely to collapse in the earthquake's immediate aftermath, giving people time to get away.)

(So maybe the foundation treatment is legit and derived from this, or maybe it's a scam that started off trading on an apparent derivation from effective technology.)
posted by XMLicious at 5:25 PM on January 25, 2017

It's not clear from your question if you have already investigated this, but the first step is to figure out WHY the cracks are developing.

1950s houses were generally built pretty well with block foundations, but improper management of water can put huge pressure on your foundation walls and this can cause cracks.

The first thing I would do before spending big money is make sure you have proper water management, including gutter systems, landscaping sloping away from the house, and if needed, underground drainage systems.

After the water is controlled, measure the cracks over a year or two with masking tape over the cracks with the crack width marked. If it's the same crack 2 years later, it's nothing to worry about.

If you are really concerned about these cracks, and they are so large you can get your hand in them or the wall has a bow so significant that upper stories are affected, I would first call your friendly neighborhood structural engineer that is selling nothing more than advice.
A structural engineer can also suggest the correct fix (if any is needed at all) for your situation.
posted by littlewater at 6:44 PM on January 25, 2017

I definitely suggest a structural engineer as a first step. It should only take a little bit of time and not a lot of money. We have a poured foundation in a house that was built in the late 1930s. There was a handful of cracks in our foundation that were leaking when there was a large, prolonged rain storms. The engineer quickly identified that we didn't have any structural flaws and the cracks were minor and expected based on the age of our house. He recommended several companies that did an injectable expanding foam that sealed the cracks through the width of the foundation. The repair was less $200 per crack and they were done in less than an hour.
posted by mmascolino at 8:26 AM on January 26, 2017

I'm a structural engineer. There really isn't enough information in this post to give accurate advice on your situation.

You're probably aware that foundation issues are serious and should be dealt with properly. If the problem is not fixed properly, you could easily face bigger problems down the road, potentially throughout your house. Obviously I'm biased, but I would recommend engaging a local structural engineer who does residential work to make a site visit and provide a letter recommendation for you. The structural engineer would come to your house, take a look at the cracks (the size, location and orientation of the cracks are all important and would point to different causes of damage), take a look at the house more holistically, look for evidence of leaks, soil movement or subsidence around your foundation, a few other things. After the inspection, the engineer would look into any available soils information, probably run some simple calculations, might look into any available record drawings for your house (if they exist), and write up a letter for you with their analysis of why your house is damaged and with recommendations for repair. Depending on your region and the local market, this would likely cost you somewhere between $1000 and $2500. As mmascolino mentioned, the repair might end up being simple, or it may need to be more complex.

I've designed carbon fiber applications on masonry walls before in some particular scenarios. Carbon fiber strips might be an acceptable solution to repair your wall or prevent the damage from worsening. Without taking a proper look at your home, any reasonable engineer would not make a definitive comment on the proper solution for your repair, as that could easily open them up to liability should you take their advice and it proves to be in error or incomplete.
posted by hootenatty at 2:48 PM on January 27, 2017

Just a quick followup -- thanks for all the answers, and the repeated advice to engage a structural engineer to analyze the situation. Via an architect friend, I'm reaching out to a couple of structural engineers he's worked with in the past to see if they're willing to take on this project.

(And I should apologize to the professionals who were kind enough to reply: I should have made it clearer in my initial question that I wasn't looking for specific advice or recommendations on my particular situation, due to the liability issues hootenatty mentions. The reply hootenatty gave -- i.e. depending on the situation, carbon fiber might have merits -- is the sort of general answer I was looking for.)
posted by orthicon halo at 7:55 PM on January 29, 2017