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Don’t underestimate the difficulty of installing concrete

A concrete patio is a more difficult DIY project than most people realize. (iStock)

Q: I plan to install a concrete patio during my vacation. It’s going to measure 14 feet by 30 feet. I’ve watched lots of online videos and paid attention to cable TV shows and now feel emboldened. What can go wrong, and how much help do you think I’ll need? I’ve never done a job like this and feel it’s doable. What advice can you add to the mix? — Ronnie S., Tyler, Tex.

A: This question reminds me of the can’t-fail spirit I relied on early in my career when I tried to do something new. It’s important to remember that back then, there were no online videos or cable TV shows to instill a dangerous sense of bravado.

The first time I tried to do a large concrete job on my own, I was 23 years old and had never done anything like it before. I was pouring a set of steps and a short section of sidewalk alone at an older home I was rehabbing. How hard could it be?

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It’s much, much harder than you can ever imagine. The first thing that went wrong: I never thought how the concrete wouldn’t flow horizontally across the truck chute to get to the uppermost steps. The top steps were just about a foot below the top of the truck chute. About half a cubic yard of concrete had to be hand-shoveled from the chute, and the truck driver was kind enough to help.

Another key point is concrete installation is true science. Scientists devote their entire careers to the study of this man-made material. Most of the online videos I’ve seen about concrete installation gloss over extremely important details.

The mix you order from the concrete plant needs to match the extreme weather you’ll experience outside your home. You will often see that 4,000-pounds-per-square-inch (PSI) concrete should be used in climates that experience freezing weather. Note this is a minimum standard. You can order stronger concrete, and it might be a good idea to do so.

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Water is both the friend and foe of concrete. Add too much at any point in the mixing or installation process, and you can ruin the concrete. Allow too much water to evaporate from the concrete after you’re washing off your tools, and you can weaken the concrete. New concrete needs to retain water — it’s called curing — so the microcrystals in the concrete can continue to grow for months after the ready-mix truck leaves your home.

Concrete is very strong when squeezed, but it has only one-tenth that strength when subjected to tension. Tension is when concrete gets bent by hollow voids under the new concrete or from frost heaving in cold climates. The addition of reinforcing steel is a must if you want to ensure your new patio doesn’t develop wide, ugly offset cracks.

Your new patio is going to shrink. Concrete tends to shrink one-sixteenth of an inch for every 10 feet. This shrinkage pulls the concrete apart and can cause ugly random cracking. It’s best to put in your own control joints in the wet concrete. These pre-weakened joints must be a minimum of one-quarter the thickness of the slab. All too often, contractors make them too shallow.

Lastly, don’t underestimate the enormous amount of work to get the concrete from the truck into the forms. You’ll need at least six or eight helpers, especially because none of you has ever done this type of work before. Pour just before the sun rises so you don’t die of heatstroke! Good luck!

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