Kevlar-Carbon Fiber Foundation Repair

[Mike Lamb]

I'll be looking at a house Monday with an inward bowed horizontally cracked poured foundation.  I am told it has been repaired with Kevlar carbon fiber straps.  Any opinions on this type of repair? 

 

[John Kogel]

I would look at the anchoring of the straps, but would not be able to tell much from looking.

If you get a company name you could research their rep.

I would look at the root cause of the bowing and try to see if improvements were made there.

Good luck with that one.

Edited July 14, 2017 by John Kogel

[Chad Fabry]

The straps are adhered to the wall using an awesome epoxy product. The repairs typically come with lifetime warranties. I've seen dozens and I haven't yet seen a failure.

[Erby]

I've only seen a couple but looked great and seems to work well.

As John said, look outside and see if the fixed the issues there also.

The way I explain it to clients is:

Take five children's blocks and lay them down in a line

Take a piece of scotch tape and run it up one end, across all the blocks and down the other end.

Stand the blocks up.  

Push on the side with the tape on it.  The other side of the blocks separate.  That's the ground (whatever the root cause) pushing against the foundation wall without any reinforcement 

Now turn it around and push on the side across from the tape.  That's the carbon fiber strips in action.

A lot of old traditional foundation guys hate it.  "Gotta use box beams buried in the cement and fastened to the structure above."

 

 

 

[Les]

Pretty common around our area.  Only failures were from improper installation aka:  skilled homeowners.  Are they all kevlar?  

 

[Steven Hockstein]

I see mostly CMU foundations around here. One of the structural engineers we work with expressed concerns about the fact that the straps are glued to the surfaces of the blocks and if the connection fails, the straps are not effective. He compared the straps to an egg, strong until there is a small failure and then...

It will be interesting to see how these systems stand the test of time.

[Les]

I often use the analogy they are very similar to strapping tape on packages.

I have also asked, and not gotten an answer from mfg, how efflorescence affects them. 

 

[Marc]

Efflorescence doesn't happen until moisture evaporates from the surface, so if the carbon-fiber isn't permeable there's no efflorescence.  Moisture just builds up within the wall until equilibrium is reached.  Just my guesswork.

The carbon-fiber is like rebar embedded at the bottom of beams that support hwy overpasses.  At the top are compression forces, at the bottom are tension forces.  Concrete does very poorly on tension forces so they embed steel in it at the bottom.  At the top of the beam are only compression forces, and the concrete handles that very well.  So if the carbon-fiber on interior basement walls works, it must be because it resists tension forces well.  Again, just my guesswork.  I guessed my way through college.  I guess I'll stop now.

Edited July 19, 2017 by Marc

[Les]

3 hours ago, Marc said:

Efflorescence doesn't happen until moisture evaporates from the surface, so if the carbon-fiber isn't permeable there's no efflorescence.  Moisture just builds up within the wall until equilibrium is reached.  Just my guesswork.

The carbon-fiber is like rebar embedded at the bottom of beams that support hwy overpasses.  At the top are compression forces, at the bottom are tension forces.  Concrete does very poorly on tension forces so they embed steel in it at the bottom.  At the top of the beam are only compression forces, and the concrete handles that very well.  So if the carbon-fiber on interior basement walls works, it must be because it resists tension forces well.  Again, just my guesswork.  I guessed my way through college.  I guess I'll stop now.

Marc, everything you write is correct, except you made an assumption that the efflorescence would occur under the strap and there would be moisture under the strap, etc.   IE:  cracked wall, water entry, efflorescence, clean the wall, apply the strap, then what?