Post tension slabs – Answers To Questions

When asked – what’s a post tension slab

What can you tell them about post tension slabs. Do you say you don’t know anything, or can you give them a short explanation about them and why more and more builders are using them.

Test your knowledge – answer these questions:

1. What is Post Tension Slab ?
2. What are the advantages ?
3. What is the “Post Tension” sign about ?
4. When did we start using Post Tension
5. What are other types of slab reinforcement

1. What is a Post Tension Slab

It is a concrete slab that has steel cables running through it that have been put under lots of stress to reduce cracking of the concrete and increases the strength of the slab.

The steel cables are usually wrapped in a plastic coating and run both directions in the slab. They are placed in the slab before the concrete is placed. Once the concrete has been poured and has had a chance to harden some and build up strength, then the cables are pulled very tight with a hydraulic jack.

2. Advantages

There are several basic advantages for a post tension slab.

It reduces cracking of the concrete. It doesn’t eliminate it, but greatly reduces it. (As we all know, concrete tends to crack over time)

It helps spread the load (weight) of the home over the entire slab area verses just on the footing area. This is a real benefit in areas of the US that have expansive soils or soils that have have poor load bearing capacity.

Cost savings. Builders will often use post tension slabs because they can save money and still provide a structurally solid home for the buyer. A Win / Win for both.

3. Why have a sign saying Post Tension: there is a really good reason

It’s Safety, plus…

There is a danger that if a non-professional cuts or drills into the slab, that they may sever, cut or damage the post tension cable. At times with out realizing it. This may weaken the structural strength of the slab. However, should this happen, it can be repaired and even if not repaired, the slab may still function well.

Safety and injury. Occasionally, if the post tension cable is cut, it may suddenly rip out of the concrete and badly injure a person. Remember, these cables are under a tremendous amount of stress. Overall, this rarley every happens, but for safety reasons contractors put up the warning signs.

4. When did we start using Post Tension Slabs ?

The use of post tension cables has been around for many years. Back in the 1960 there was limited use in concrete foundations in residential construction, but very little.

In states like California, Texas, Nevada and Arizona the use of post tension slabs have increased tremendously in the last ten years. Now in many areas they are the builders choice for reinforcing a concrete slab. They are being used more and more, especially by track builders.

5. If no Post Tension Cables, what do contractors use ?

The two basic types of reinforcement that have been used in slabs since the 1960’s has been steel rebar or welded wire mesh.

Rebar is probably still the most common form of reinforcement in concrete slabs. There is also a small but growing form of reinforcing slabs, and that is the use of fiber reinforcement.

6. The Bottom Line for buyers

Post tension cables are great for reinforcing a concrete slab, but so is rebar, welded wire mesh or fiber reinforced slabs. It all depends on what the engineer calls out and the type of soil.

David Jones - General Contractor, Home Inspector, Consultant

David has over 45 years’ experience as a general contractor, inspector and professional instructor. He writes articles for homeowners, new home buyers and Real Estate Agents. Read more