Just a reminder for new inspectors carbon fiber strips on basement walls IMO is a bad idea. For some background I did my master thesis on carbon fiber strengthening of bridges. My advisor was Dr. Antonio Nanni, which was part of the ACI Committee 440 that published design guidelines for externally bonded fiber reinforced polymers (FRP) reinforcement for concrete structures. First of all the general rule is you don’t use it as the primary reinforcement on a concrete or masonry wall. Its intended use would be to strengthen or supplement “under reinforced walls”. You don’t use carbon fiber to strengthen a wall that was designed with the correct amount of reinforcement either. To put carbon fiber on an unreinforced wall will create a situation where brittle failure can occur. A properly reinforced concrete or masonry wall is designed to let the steel reinforcement deform or stretch on the tension side before the concrete or masonry block crushes on the compression side of the wall. When too much force is applied the tension side of the wall will crack and deflect giving visual warning signs the wall is failing. A wall that is over reinforced will not likely crack or deflect instead the concrete or masonry block will basically explode on the compression side called a brittle failure. To properly apply carbon fiber you need to know the size and placement of any internal reinforcement and you need to know the concrete or masonry block strength. None of the foundation repair companies have anyone on their staff that can do that. Bonding strength of the carbon fiber is critical so proper cleaning and application if the carbon fiber is very important. Another important step these companies leave out is performing a bond strength test. This test involves epoxying a 2” steel plug on the cured carbon fiber then use a diamond hole saw to cut the carbon fiber around the steel plug and use a calibrated tension device to pull the plug off the wall to verify the adhesion. So you don’t see any of these foundation repair companies talk about these other requirements to properly use carbon fiber. Sorry for the long explanation, but the devil is in the details they leave out.
Not good for submarine hulls either!
Great explanation Randy.
To tack on to this, it is well known (at least in my area) that carbon fiber warranties are voided if the block gets wet. I once locked horns with a salesman from one of biggest carbon fiber companies in the Northeast in a client’s basement. He was trying to sell it. I was advising my client against it. I straight up asked him about the void clause if the block got wet. He said “why would the block ever get wet.”
It’s also been proven that CFRP reinforced concrete and masonry experiences a 33% reduction in load bearing capacity when exposed to moisture, compared to a dry state (“Durability Evaluation of CFRP Strengthened Concrete Beams: Experimental Study and Design,” ACI Structural Journal, Feb 2005). Not only that, but the ultimate failure and destruction of the test pieces occurred not in any related way to the strength of the underlying masonry, but at the exact moment the carbon fiber resin de-bonded from the masonry.
University of South Florida also did a 20 year study on CFRP strengthened CMU walls, and pull out tests proved the mortar joints and the condition of the CMU units were the weak links. Unfortunately that study only looked at walls with vertical settlement loading only (CFRP in shear), and not with load schemes that you would see in a basement foundation, where the CFRP would be constant tension.
Plus, ACI has addressed this moisture issue explicitly:
“FRP systems should not be applied to concrete surfaces that are subject to moisture vapor transmission.” - ACI Committee Report 440.2R-02
“FRP materials subjected to a constant load over time can suddenly fail after a time period referred to as the endurance time. This type of failure is known as creep-rupture. As the ratio of the sustained tensile stress to the short-term strength of the FRP laminate increases, endurance time decreases. The endurance time also decreases under adverse environmental conditions, such as high temperature, ultraviolet-radiation exposure, high alkalinity, wet and dry cycles, or freezing-and-thawing cycles.”
This is why you don’t see long-term CFRP use in the commercial market anywhere near a foundation wall or in wet service.
Sounds literally like a Band-Aid solution.
Yet another in the long line of “fixes” offered by foundation contractors meant to sell consumers with some big words or new tech.
Some great information in this thread about carbon fiber strip foundation repairs and reasons, albeit technical, why they should be called out when found.
Exactly what it is.
Appreciate the added good info Darren. 
Yeah, Kevin, for sure.
Morning, Randy.
I doubt many inspectors have seen FRP on foundations so I thought I would post an image.
Ouch, but apparently true!
This a great thread and thanks for the info. I only see CFRP once every other year and at least once was obviously a DIYer. But I did not know about these issues. We are pretty dry here, but our foundation walls always have high moisture content. This year with our record rainfall, damp foundations are everywhere.
I along with Robert wanted to show some images of what you are referring to.
I have not come across this type of repair so far… Thanks Randy and Darren for sharing your knowledge, it helps us all!!!
Great information.
Now, as a home inspector how do you translate this to a client? More specifically, when is it a material defect?
Another example is interior foundation drainage systems which are often mislabeled as a “foundation waterproofing system”.
It seems we would have to identify some sort of failure in the system or adverse conditions that will negatively effect the performance, such as damp/wet conditions, loss of adhesion or visible damage. Otherwise, shall we just move along?
Another consideration. If a home inspector has an objection to this type of system, I recommend being prepared to defend your objection. Because these rip-off foundation companies will surely give the system a clean bill of health. One way to accomplish this is to have the document that Darren provided.
Keep in mind, there are newer versions. Here is a link to the latest version I could find.
This guide may also contain valuable home inspector information, if you are ready to join ACI or pay the $95
On carbon fiber just recommend the seller have the installer provide documentation on existing reinforcement placement, concrete strength testing and adhesion tests.
Great article Randy, thank you for your expertise.
The answer back will be the sound of crickets.
Thank you very much Randy. I’ve only run across this 2 or 3 times over the 10+ years I’ve been inspecting and was not aware of this issue. I’ve added language for this to my report template.
Completely agree. I worked as an engineer for most of my career in aerospace much of it in carbon fiber composites.
When carbon fiber fails, it generally fails catastrophically. Boom chacalaca. Done.
You should hear the lab when we are ripping samples apart and crushing them during testing. Sounds like explosions going off.
That’s why airplane parts made from carbon fiber composites are over designed so much. Can’t afford a failure.
It’s a great material if used appropriately. But, it doesn’t fix everything.
Great image, Neil. I was looking for interior foundation reinforcement strips.
Great work as always, Neil. Thanks.
Since we dont have many basement’s here… Instead of carbon fiber what are people using?
Steel plates or straps.