How to Remove Concrete to Create a Garden
Concrete is great stuff, and it deserves its title as King of Building Materials, but some homebuilders (and remodelers) can use it to excess. If you’d like to look out your backdoor and see wildflowers and herbs instead of a sweltering gray slab, you’ll be glad to know that while concrete slab removal is a backbreaking job, it’s not skilled work. Most people can remove concrete themselves, provided there’s plenty of ibuprofen and a heating pad in the house. Find out how.
What’s In a Slab?
A typical outdoor concrete slab ranges from 3-6 inches thick. Patios and stoops tend to be on the thin side, with driveways at the thicker end of the range. A slab may contain reinforcing metal, in the form or wire mesh and/or rebar. There’s no way of knowing what’s in there until you start breaking up the concrete. You might get lucky and have no steel in your slab (even the country’s most famous house, Fallingwater, was originally built with a lot less steel than the plans called for). Below the slab is a compacted gravel subbase. This might be a few inches thick or a lot thicker, depending on the site conditions. After you break up and remove the concrete, you’ll have to dig out all the gravel, to make room for plant-nourishing soil.
How Concrete Breaks
Concrete is strong, but it’s also brittle. You can hammer all day at the center of a slab—where the concrete is evenly supported—with no appreciable effect. But if you hammer at the edge of the slab, where the ground underneath can shift or be displaced a little, the concrete will break. This is because you’re essentially bending the concrete, which is its main weakness. If you want to break up a large piece of concrete for removal, pry up one end and set it down on some rubble or a scrap of timber, then strike the piece in the center.
Options for Removing Concrete
Here are the three main methods for homeowners, from easiest to hardest. Talk to your trash removal company and local dumps to learn about options for getting rid of the concrete rubble and gravel subbase.
1. Hire a concrete demolition company.
Hire concrete professionals, who have the experience -- and the equipment -- to saw, smash, and remove a slab in no time. The pros can also dig out the gravel subbase down to the soil.
2. Rent an electric demolition hammer (a.k.a. chipping gun).
These mini jackhammers are relatively lightweight and easy to handle and are available at any rental outlet or home center. Work from the slab’s edge toward the center, breaking off manageable chunks with the hammer. Use bolt cutters or heavy-duty wire cutters to snip reinforcing mesh; cut through rebar with a handheld grinder or reciprocating saw.
3. Use a sledgehammer.
If you were especially vehement in rooting for John Henry to defeat the steam-powered hammer, this might be your preferred method. Follow the same tips given above for the demolition hammer. And don’t work so hard that you end up like John Henry at the end of the story.
You may have heard about the technique of drilling holes in concrete and filling them with expanding mortar to break up the slab. However, this is really for big commercial jobs where blasting or other methods are undesirable. For you, drilling 1-inch-diameter holes throughout a slab is as much work as using a demolition hammer, but it adds an extra step and more expense.
If You Need to Cut the Concrete
If you want keep some of the slab intact (perhaps to create an “island” planting bed or to protect surrounding structures), you can rent a walk-behind concrete wet saw (with a diamond blade) like the pros use to cut through slab. Make the cuts before demolishing the rest of the slab, and follow the manufacturer’s and rental company’s instructions carefully. As mentioned, you can also hire out this work.
Prepping the Ground for Plants
Most plants need at least 6 to 12 inches of healthy soil for growth, plus 1 to 2 inches of mulch (if applicable). Dig your planting area to the appropriate depth, then fill it with the recommended blend of soil for your area and planting goals. The best resource for specific recommendations is a local university extension service (or a master gardener or landscaper, should you happen to know one).
Updated December 24, 2017.
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