The three basic methods of underpinning a residential foundation, be it concrete slab or pier and beam, all have their critics. Remember, underpinning is the process of getting piers (or pilings) under the foundation to shore it up.
When you are researching foundation repair cost per pier you’ll find quite a difference in price depending on the type of pier the contractor or engineer recommends. The mix also includes the Millennium Composite Piling System (TM)
Among the most basic is the bell bottom or drilled pier. It’s been around for a very long time.
Workers generally dig out spaces along the edge or beam of the foundation at specified intervals. Once enough space has been created, 2-man teams will begin motorized drilling to make a 9-10 inch shaft down to stable soil, usually ten to fifteen feet.
Then a “belling” tool is sent down the shaft to dig out a wider footprint, about 24 inches in diameter in the shape of a bell. This fat footprint is supposed to add an extra degree of strength and stability.
Steel rebar is added to the shaft and bell which is then and then filled with fresh concrete. The top of the shaft is leveled off, the concrete is allowed to dry and cure resulting in a pier.
And the critics say..
It takes too long. A day or two to create the piers depending on the size of the foundation. Another few days to a week for the concrete to properly cure, weather being a factor, another day to jack the foundation and add the shims. Plus, the critics howl “It makes a hell of a mess around your house.”
Especially if piers are needed inside the home, say the middle of the living room or kitchen.
But bell bottom piers are an old tried and true method of foundation repair and some contractors swear by it and only offer this method.
Pushed Concrete Piers
One of the most common and cheapest methods of underpinning in heavy clay soils are pushed concrete piers. Space is dug out along the edge of the foundation, often at six to eight foot intervals. If interior piers are required flooring is removed, and a hole is cut out of the slab, soil removed and same same process described below is used to make the pier.
Machinery is then used to “push” pre-cast concrete cylinders, also known as caissons, one on top of the other in a stack. The foundation itself is used as the fulcrum. The cylinders are shoved down until they won’t go any deeper, or the “point of refusal” in foundation repair lingo. This creates the pier or piling.
A concrete cap is added to the pier. Then using jacks, the crew will raise the foundation to the point of level and metal shims are added to fill the space between the cap and the slab.
The jacks are removed, the soil is filled back in, landscaping restored, area around the foundation is cleaned up and they are done. The average size house is usually done in a day unless interior piers were installed. In that case the hole(s) chopped out of the foundation need to be filled back in with fresh concrete and allowed to dry.
The critics of pushed piers say:
The piers don’t go deep enough. You just can’t shove the blunt end of those cylinders that far down using the weight of the house as the fulcrum. “Skin friction” isn’t enough.
If one of the cylinders breaks or cracks you can’t see it. The point of refusal may come because of a big rock you can’t see. The first cylinder may be deflected resulting in a pier that is not straight down. So on and so on.
Steel piers or pilings are basically galvanized or epoxy coated steel pipes that are driven to a depth that reaches bedrock or otherwise stable soil. The piers are ultimately attached to the edge of the slab foundation with steel brackets once it has been raised to level with hydraulic jacks, same as the other methods of repair.
The helical version of steel piers have a screw like foot that is twisted into the load bearing stratum like a corkscrew.
The Critics of Steel Piers Say:
They can be too flexible. They can be deflected out of vertical by unseen rocks or changes in stratum, veering off a straight patch. They can bow and bend.
I couldn’t find any hard data on how often this sort of thing happens. I’m guessing not very often. But it did set some people thinking about building a better mousetrap as it were. So here comes:
The Millennium Piling Systems™
These piles are a combination of steel, concrete, epoxy with a PVC sleeve with more concrete. They come in three flavors, with the steel composite pilings being the most elaborate.
With this system, the “starter” piece of the pier, the first section to be driven, has 3-point wings designed to keep it from veering off vertical and keep it straight.
The steel pipes have an inner PVC sleeve that holds epoxy coated rebar and is filled with concrete. They kind of look like concrete pushed piers with a coated steel jacket.
They are installed pretty much the same way as pushed piers with hydraulic machinery that shoves them into the ground using the slab as a counter weight.
The cost of foundation repair using this type of pier? You might think it would be pricey, but that doesn’t seem to be the case. I went through customer reviews on Angie’s list of a company in the Dallas area that uses the Millennium pilings.
Some of the reviews listed the number of piers and the total cost. The math shows the cost of the millennium piers falling between pushed concrete piers and steel pilings.
Are there critics of the Millennium piers? Of course. They claim that these piers will outlast the life of your house. In fast last a thousand years, hence the name.
The claim is also made that less than 1% of foundation repairs using these piers have to be revisited and re-adjusted. It makes you wonder that if these piers are so great, why more foundation repair contractors don’t use them.