Concrete deck piers can rise above soil level
Tim Carter
Q: I’m concerned about the concrete deck base that is fully above ground at my new home. The other decks in our development have the concrete piers below ground. Shouldn’t the concrete be completely buried to protect against freezing and cracking in the winter months? What do you think are the best concrete deck foundation details?
— Jeff K., Falling Waters, W.VA.
A: I can understand the concern. It’s not far-fetched to worry that your deck foundation piers are wrong when they are the only ones that look like it in the neighborhood.
But think about this: Is it possible that your carpenter was the only good one in the development, and the others were ill-informed? You bet it’s possible.
The photos sent to me show that the builder or carpenter got everything right as far as what is supposed to happen above ground. It would take less than an hour with a round point shovel to determine whether the deck pier extends below the frost level and has a wider concrete footing that the circular deck pier rests on.
Let’s discuss deterioration concerns first. Concrete is an artificial, man-made rock. If it is mixed and installed properly for the local weather conditions, it can last for hundreds of years. It’s all about adding enough Portland cement to the mix and making sure you don’t add too much water or use water to finish the concrete. Curing the concrete to slow the release of the mix water also is very important.
Frost heave is another concern. Soils that contain water in freezing climates can expand, and they go up in almost all cases. Ice lenses grow and grow, pushing the soil above them higher as the bitter weather drives the frost deeper in the soil.
You want your deck piers to be below the frost level so the deck doesn’t lift up. This kind of unwanted force can cause severe structural damage to the deck.
I have worked with many architects and engineers in my building career. Most of their plans agree: It is important to spread out the concentrated load of the deck posts across as much soil as you can. Usually, a 6- or 8-inch thick, 2-foot diameter poured concrete pad below the frost depth is sufficient to distribute the weight of the deck.
There are all sorts of ways to install a deck foundation base or pier. The most ingenious method I have seen to date is a plastic deck pier form you snap together on the job site. It even comes with all the required pre-bent and pre-cut reinforcing steel rods.
This deck pier form is designed so its base is flared out at the bottom so it spreads out the concentrated load. You just dig the hole to the correct depth, make sure the soil is compacted, set the form in place, and then immediately backfill around the form with the soil you just dug out of the hole. Add this soil slowly so you make sure the form doesn't move. You then fill the form with the concrete, place the anchor bolt for the post base and wait one day to start building the deck.
I prefer to have the top of my concrete deck piers at least 4 inches above the final grade around the piers. I don’t want my treated lumber posts buried in the soil. I always use a galvanized steel post base that keeps the bottom of the wood post up and off the poured concrete. This allows water to drain away from the wood.
Q: I need to install a wrought iron handrail down an exterior stairwell. One of the mounting brackets will be on the poured concrete foundation wall but the other one must be on the exterior brick. I don’t want to ruin the brick, and realize I must get this right the first time. What would you do to prevent the handrail from pulling away from the wall? — Ken B., Homewood, Ill.
A: You do usually get only one chance to get this installation right. Ideally it would have been best to put in through bolts in the masonry walls, but this is also extremely problematic.
I’ve tested all sorts of masonry anchors through the years and some are far better than others. Lately I’ve had the best success coupling wedge anchors with high-strength epoxy. A wedge anchor looks just like a normal threaded bolt at one end. However, the business end of the anchor has a coneshaped end and a secondary steel sleeve fits over the cone. As you tighten a nut at the end of the anchor it pulls the cone-shaped end into the sleeve, causing the sleeve to grow in diameter and wedge itself into the masonry.
This friction helps offset the pulling force exerted by the weight of the handrail and anyone pulling on it. However, I’ve had failures with just using the anchors alone, so I tested a new method where I angle the hole as I drill into the masonry. I move the drill left and right about 15 degrees off center to create a hole that is much wider and deep in the masonry than the small diameter hole that you can see on the face of the brick or concrete.
I blow out all the grit and use a bottle brush to make sure every bit of dust is removed from the cavity. I then squirt in a special concrete epoxy so the hole is just about filled. I coat the wedge anchor and then push it into the hole so that some of the epoxy squirts out. I clean off the epoxy and allow it to cure for 48 hours.
Tim Carter writes for the Tribune Content Agency. You can visit his website (www.askthebuilder.com) for videos and more information on home projects.