Ask the Builder: Fixing puddles on patios, driveways and slabs
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Ask the Builder: Fixing puddles on patios, driveways and slabs

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Here’ s a pesky puddle on an outdoor patio.

Q: I’ve got a problem I need you to solve. Each time it rains, a puddle develops on the outer edge of my circular patio. It’s older concrete, and it appears the puddle is related to a crack that’s above a low retaining wall the patio rests on. Can I just fill in where the puddle is and all will be well? I am worried about the appearance of the patch. How might I disguise my attempt to stop the ponding water? I only want to fix this one time. What are my options? —Amy P., Warrenton, Va.

A: I see puddles frequently and even have the issue here at my own home where there are depressions in my asphalt driveway and where my front sidewalk meets my drive. (I didn’t build the house I currently live in.)

The patio repair is not that hard to do, but you threw in a wildcard with respect to what the repair will look like. You want your patio to look nice and not like a hodgepodge of different colors and textures. Judging from the excellent photos you sent, I can tell you that it would be next to impossible to install a patch that blended in perfectly. (You can see all the photos at AsktheBuilder.com.)

There’s another issue in play. You mentioned there’s a crack in the patio that’s directly related to the low curved retaining wall. And you also want to make the repair once. Failure is not an option.

When you add all these pieces of the puzzle together, you only come up with one repair option in my book. You need to do a thin — perhaps just 2 inches — concrete overlay.

Concrete overlays can come in a variety of flavors. You can do one as thin as a coat of stucco! This means the overlay is really just fine sand and cement. It’s possible to get the overlay as thin as 1/8 inch, but 1/4 inch would be an easier project to manage for the DIYer inside you.

If you hired me to write the simple set of specifications for your job so you could get really accurate bids and be sure the job would be done right here’s what I’d go with.

I’d want the concrete overlay to be 2 inches thick where it starts at the outer edge of the concrete patio where it passes over the low retaining wall. Before I’d even start to do the work, I’d cut a scrap piece of wood 2 inches thick and place it on the outer edge of the patio. Then I’d rest a straightedge on the small piece of wood.

I’d want to check to see how thick the overlay would be when it got back to the house, making sure the patio had a consistent slope of 1/8-inch per foot. This way rainwater would drain off the patio with ease. You can get by with 1/16 inch per foot, but it takes an expert concrete finisher to maintain this slope and not create a new puddle in the middle of the new overlay! After all, you want this repair done once.

The concrete would have small pencil reinforcing rods in it. These rods are 3/8 inch in diameter. I’d prime and paint them with a rust-resistant paint before the job would begin, as I don’t want the rods to start to deteriorate in case you broadcast salt on the patio in the winter months. These rods must have at least 1/2 inch of concrete under them when the overlay is poured.

I’d make sure the spacing of the rods was 2 feet on center in both directions. Imagine creating a giant piece of graph paper but using the steel rods as the lines. This steel ensures the overlay will stay together as one piece and not have settlement issues where part of the slab drops lower than an adjacent piece as is happening over the retaining wall.

The size of the stones in this concrete overlay is critical. I’d not want any stone to be larger than 3/8 inch in diameter. Some gravel pits sell a gravel called pea gravel where the stones are round and about the size of small grapes, none being larger than 3/8 inch in diameter. You can also use small crushed gravel that is a similar size.

I’d specify a seven-bag mix, which makes the concrete stronger than the minimum 4,000 pounds per square inch strength recommended for outdoor slabs in a cold climate. My specifications would also state to be sure to pressure wash the existing concrete patio to get a great bond between the old and new concrete.

I’d list as an option the application of a thin layer of cement paint to the old, damp concrete before the pour. The steel rods make this quite problematic. If you have enough helpers present, you can do this cement paint application with them brushing it on the damp concrete just before it’s covered with the new overlay concrete. You make cement paint mixing pure Portland cement with water until it’s the consistency of normal paint.

Keep in mind you can add color to the concrete! You can buy dry-shake pigments and make your new patio look like leather or even the sky!

(Subscribe to Tim’s FREE newsletter and listen to his new podcasts. Go to: www.AsktheBuilder.com.)

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