Post Tension Foundation
The decision as to if a post tension (later refered to as “pt”) foundation is required for your particular construction project is a decision that should be made by the engineer responsible for the foundation plans. At no point should you decide against post tension cables as a cost saving mechanism. You need to move forward exactly as the engineer has specified and you should not deviate from the engineered plans under any circumstance.
Post tension foundation cables are to be installed after the form sand is covered and sealed with the foundations poly vapor barrier. It is important that you install the foundation cables prior to the completion of the forms being floated, since having float boards will likely interfere and impede the installation of the pt cables.
At this stage in the process, unless you have selected a turn-key concrete contractor who is responsible for all aspects of the foundation, you will be responsible for furnishing the materials required for the post tension system. These materials typically consist of 1/2″ steel cables in greased plastic sheathing (often labeled and identified by supplier as to the location in the foundation each cable corresponds with); pocket formers; plastic chairs; S-hooks; catheads; and steel anchors. One end of each cable (the dead end) will have a steel anchor permanently secured to it. It will be between you and your concrete contractor as to the responsibilities of the cables. It would be a good idea for you to have a fine tuned schedule where the cables will be arriving the day the contractor will need them and have them installed.
During the installation of the cables you will notice the contractor will drill holes in the form boards as indicated on the foundation plan and routes cables in the desired locations; nails and secures the dead ends to the foundation form boards; then assembles and installs anchors with pocket formers at the live ends. Proper cable tension is assured by securing catheads on the outside of the form boards. Plastic chairs are also installed under each cable. Typically the concrete contractor will provide the nails and tie wire responsible for securing the post tension cables to the form boards and securing the intersecting pt cable locations together.
After the completion of the post tension system you may also be required by the slab engineer to use additional steel reinforcement (rebar) and welded wire mesh, due to soil conditions as deemed appropriate by the engineer. It is important that you carefully review the foundation plans, beam details, and additional notes provided by the foundation engineer.
