Sewer Line Repair under a Post-Tension Slab

by stevensplumbingac on March 22, 2014

Sewer Line Repair under a post-tension slab is a complicated plumbing repair.

And unfortunately it’s a  more common problem than you might think.

Questions?  Give us a call!  (602) 273-7473

A post-tension foundation is one that has high-strength steel strands or cables (called tendons) laid within the poured concrete, in a grid formation. These tendons help support and give strength to the concrete once it has cured.(1)  Builders in the Phoenix area have been using the post-tensioning process in home building for over a decade now.  Post-tensioning decreases the chances of your concrete slab cracking, which is why so many residential contractors are now turning to this process for the homes they build.  Many homes – maybe even yours! – are built on a post- tension slab foundation.

sewer line repair under post-tension slab where root damage at phoenix homeWhile the post-tension process produces a high quality slab foundation, problems can and do arise if anything goes wrong with the drain and/or sewer pipes located beneath the slab. 

The most common problem we typically see with drain or sewer lines that need repair is roots that have grown into the line and caused damage.   The picture on the left shows just such a situation – large roots had invaded the sewer line and cracked the pipe. 

The roots had to be removed, and the damaged sewer line replaced.

Access to a sewer line under a post-tension slab can be a huge issue.

Whether you’re dealing with root invasion, or another problem such as movement caused by expansive soil,  replacing or repairing sewer pipes under a post-tension slab is an issue, because access to the sewer line is limited by the tendons in the slab.

If your home has been built on a post-tension slab and your drain or sewer lines need replacement or repair, you’ll want to call a plumbing company that has experience repairing and replacing sewer lines under a post-tension slab – like Stevens Plumbing Heating & Air Conditioning.

Sewer line repair under a post-tension slab foundation requires experience and knowledge.

roots crushed this sewer line under post-tension slab in phoenix houseStevens Plumbing Heating & Air Conditioning has the experience needed to repair or replace a damaged sewer line that’s located under a post-tension slab foundation.

The photo at the left is of a job we did recently at a home in Phoenix.  The sewer line had cracked due to root invasion.

Because of the location of the damage to the sewer line (near the center of the house), almost the entire drain system in this house was affected.  And, because the break in the sewer pipe was located under the center of the house, the only possible access to repair the sewer line was through the home’s post-tension slab.

Locating the tendons in the post-tension slab where the sewer line is damaged.

roots damage sewer line repair under post-tension slab after tendons are located electronicallyOur first step was to electronically locate the tendons.  The home was built about twelve years ago, when post-tensioning was relatively new.  At the time, most of the slabs that were post-tensioned had tendons installed on a four-foot grid, and that was the case with this home. 

After locating and marking the tendons in the area where we had located the sewer line damage, we were able to work with an engineer to design a plan for accessing the sewer pipe.

With the tendons clearly marked, we had sections of the slab sawcut and removed so we could access the damaged section of the sewer line.  This phase of the job is probably the most difficult.  It’s critically important that the tendons aren’t cut; the sawcutting needs to remain at least six inches from where the tendons have been located.  The closer together the tendons are installed the more difficult the access (some post-tension slabs have tendons on a grid as small as 2 foot x 2 foot making access under the slab nearly impossible!).

Precise locating of the sewer line under the post-tension slab leads to a smooth repair.

sewer line repair at phoenix homeOnce the slab had been opened up to provide access to the damaged sewer line, the repair went smoothly, and included removal of the roots that had damaged the line, as well as application of salt crystals to discourage future root growth.

When the repair was complete the areas where we had excavated to expose the sewer line were shaded and backfilled and the soil compacted.  Then, to make sure the final job met all building code standards, and per the engineer’s specifications, a concrete slurry was poured in level with the bottom of the slab. 

Finally, finish concrete was poured to repair the slab, the carpet was re-laid, the job was cleaned up thoroughly, and the home was back to fully functioning!

Questions about sewer line repair under a post-tension slab?  Call us!  An experienced plumber is always available during business hours to answer your questions.

Stevens Plumbing Heating & Air Conditioning
(602) 273-7473(602) 273-7473

(1) http://www.wisegeek.org/what-is-a-post-tension-slab.htm

 

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