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Question DetailsAsked on 2/24/2017

Would carbon fiber and sika work in repairing cracks on stem walls with exposed rusted rebar?

My foundation stem walls have vertical and horizontal cracks. In some areas there are exposed rebars which are badly rusted. The concrete on those areas are crumbling. In some my readings, it states that carbon fiber will only work if the surface is clean and hard.

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2 Answers


True - if it works at all. The carbon fiber reinforcement technology is not totally snake oil, but close to it as commoinly applied to foundation walls.

There is a place for carbon fiber, especially in reinforcing concrete columns against earthquake damage and in boats and aircraft, but narrow strips glued to failing foundations is not the place for it. Unless the design has been done by an INDEPENDENT (not working for the contractor) Structural or Geotechnical (Foundations and Soils) engineer (and you will be hard pressed to find a qualified, licensed engineer to support common use of it on residential foundations), I would say you are wasting your money, because generally what is done with carbon fiber is worth about as much as the other "miracle of technology" paint-on coatings that some contractors and salesmen claim will fix your failing wall.

The main selling point they use for carbon fiber is that it is "up to 10 times as strong as steel" - forgetting to tell you that is per square inch and they are only putting a fabric-thin piece on the wall, not a structural-sized element, so the total force it can take is minimal compared to traditional structural repair methods. Also, regardless of how strong the carbon fiber may be, the epoxy it is commonly put on with has nowhere the strength to develop the full strength of the fiber - hence the pictures you see on the web of the fabric peeling off the walls as the wall continues to buckle.

Also - structurally - this is basically like putting a piece of tape on the surface of the wall, and provides minimal structural support to the wall because it is flat to the surface. It requires a moment arm - some "depth" to the reinforcement (like beams) to resist bending - or tied-backanchors through the wall into the undisturbed soil outside the foundation, holding supporting posts or beams tight across the wall to actually hold it up. The way most of the applications are done, not only can they not, as installed, begin to produce a meaningful reinforcing load, but the way it is applied (right along the inside surface in tension) provides little if any restraint against the wall failing further. Many of their disclaimers acknowledge this - commonly stating that if the wall bows more than 2 inches for instance then the system willnot work. Well - a clue - because of the way it is applied, it can not do anything significant until the bowing is more extreme that that in the first place - and if the movement gets to the point the straps actually provide some effective restraint to wall bowing then it has moved enough that you are going to have significant structural problems in the house, and probably eventual foundation failure anyway. Basically, it commonly comes down to a case that if the wall is so seriously in distress that it needs reinforcement, it should be radically repaired or replaced - not have a bandaid put on it. And for what many vendors charge for these systems, it appears the pricing is commonly based on say 80-90% of replacement cost, so generally total replacement of the failed section(s) isnot that much more expenisve and gives you a new, functional wall that you can honestly say in a reall estate disclosure that it has been replaced with new - not band-aided.

That brings in another factor commonly not addressed - the resale effect on the home. Any sort of reinforcing visible on the wall (be it carbon fiber strips, beams, tiebacks, or whatever) or reported on the disclosure is a major red flag to inspectors - not to mention the aesthetic factor and, with most systems, some loss of usable basement dimensions as well.

And the exposed rusting rebar - which likely means they are either placed wrong (too close to the surface) or that you have salty or reactive concrete which is likely pattern cracked and spalling (liek it sound yours may be), means you might be trying to reinforce a wall that might end up being a total waste of time. Certainly, at a minimum, the deteriorated concrete has to be removed (if only surficial) and the rebar cleaned up to acceptable bonding standard (commonly with sand or shot blasting ot remove all loose scale and rust, though does not have to be totally rust-free) - though since you say "badly rusted" you likely have enough loss of material that they would be considered unacceptable - meaning rebuilding of the wall would be recommended. Then, if the rebar is usable after cleanup (which is no guarantee) the concrete is repaired with a patching grout. Sika does in my opinion make about the best products around for that - I have specified their products for scores of years on jobs around the world.

I would do yourself a favor and pay the $250-500 or so for a Structural or Geotechnical engineer (Structural Engineer is the only applicable Angies List Search the List category for this) to do an on-site assessment and recommendation ofthe wall and what is happening to the house too because reinforcing the wall as is may not solve existing problems it has caused in the house, or may not be supporting it correctly any more. I would give about even odds he will say that replacement of the wall or totally rehabbing the concrete and steel with possibly an additional poured-in-place overlay of concrete (typically 3-6 inches thick) to form a thicker, stronger wall is going to be your best solution. My guess - jacking up the house and total replacement of the failing sections (or maybe entire foundation if bad construction or concrete is the cause) will be the recommendation.

Answered 3 years ago by LCD



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Answered 3 years ago by Member Services

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