For the past forty years or so severally bowing walls, from water damage, were stabilized by one of two methods. They were either dug out on the outside where the soil, which was putting the pressure against the wall, was replaced with crushed stone (which can absorb the expansion of the adjacent soil by movement of the spaces between the stones), or by steel braces which were used inside the basement to reinforce the wall.
Since the advent of carbon fiber reinforced polymer laminates (CFRP) which have extremely high tensile strengths new materials have become available to waterproofers which can be used along with traditional steel braces or in place of them to reinforce bowing walls.
These carbon fiber reinforced fabrics or plates are epoxied to the wall. They can be installed by the manufacturer or the waterproofer, or the homeowner – in a kit form. They are competitive in cost with traditional solutions. One of the advantages of such a system is that it is flush to the wall and can be painted over, thus is much less obtrusive in the room than steel beams.
These systems can also be used externally, although the wall has to have an open, prepared surface for them to be applied. In most cases this means it must be dug out to the footer. External carbon fiber reinforcing systems is usually combined with the installation of crushed stone. This is not inexpensive but removes the pressure from the wall.
These (CFRP) systems were initially used where cost was not a major factor, as in specialized industrial, commercial or historical cases where the primary consideration was getting the wall reinforced without altering the structure more than was absolutely necessary. These systems have been used extensively in earthquake prone regions to reinforce support columns, walls and support elements of all sorts. Although they are not visibly intrusive, they add an enormous amount of strength and can bring old structures up to new building codes. Carbon fiber reinforcements offer greater tensile strengths and never corrode or rust like steel.
Bowing in a wall is caused because the lateral external soil pressure is greater than the strength of the wall. Normally, over time, this continues to get worse resulting in wall cracks, basement seepage and basement leaks. To determine the amount of bowing in a wall, measure it with a plumb bob or string, hanging straight from the joist at the top. The hanging string should touch the wall in the middle or wherever the bowing is greatest. The distance between that plumb bob point on the floor and the wall is the amount of deflection.
CFRP applications consist of a strap or plate of carbon fiber laminate which is epoxied to the wall. When applied, the adhesion of the layer of carbon fiber is improved by the primer coat of fluid epoxy which penetrates in to the masonry or concrete. The straps keep the wall from stretching and reinforces its overall strength. The straps or plates are usually applied at 4′ on center distances as per The American Concrete Institute’s (ACI) design guidelines. Individual criteria can vary the distance by about a foot depending on type of soil, height of backfill, thickness of wall and height of wall, which determines the approximate pounds of pressure per inch per width and the recommended spacing of carbon reinforcement required to resist those pressures. Each basement is unique with its own specific requirements.
Carbon fiber laminates are used rarely if the bowing exceeds two inches. You may want to consult a structural engineer if that is the case. It is important not to ignore a bowing wall, as the wall will probably continue to move and given time very well may collapse. Several option as mentioned are available. The wall can be dug out on the outside, removing the pressure, steel braces can be used in addition to the carbon fiber laminates, tie-back wall anchors, or rebar grout fills, could also be used. Note however, that none of these will remove the external pressure from the wall. The only way to do that is to remove the soil and replace it with a field of crushed stone, which will absorb the pressure as mentioned above.
The choice of flexible carbon fabric or semi-rigid carbon plate depends on the structural variables of each situation and the relative cost of installation, as well as whether or not the homeowner wants to have beams adjacent to the wall, both methods can adequately do the job. The cost of these systems is determined by the number of straps one needs. A rough estimate to have them installed is $350 to $500 per strap. They are available in kit form and will cost approximately $130 to $160 per strap to do it yourself. The installation, however, is not simple and if you are not the “mechanical” type, you want to be sure to have someone help you who is. There are many manufacturers and dealers in these CFRP systems who can be found on the internet, Rhino Carbon Fiber Wall Supports, Fortress Stabilization Systems, The Reinforcer (Nationwide Reinforcing), and StablWall are the leaders.
Note: Fiber reinforcement systems cannot be used to stabilize the wall if the top or bottom is moving inward. This may be indicated by a freeze crack near the top, from the freeze thaw cycle, or a more serious structural problem. Carbon fiber straps will not resolve structural failings. If the top or bottom of the wall has broken off the bottom or top block, this is a more serious problem which will probably require the wall to be replaced, as the wall has lost its strength. Broken blocks across at the top or bottom should be looked at by a structural or civil engineer. You may want to check out http://basementwaterproofinginfo.com for additional information on bowing walls, how to tell what the various cracks mean and various solutions.
Source by George Jenney