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Does Your Slab Need Control Joints?

Good question indeed! If it does, this is the time to put them in. (You can see them in driveways to see what I'm talking about.) Here's the rule of thumb: say you're pouring a slab for a patio. If it exceeds 10 feet in any given direction, then you should use control joints.

It's Time to Pour the Concrete into the Form

Home improvement stores and tool rental outlets will rent you a portable cement mixer. This is the best way to go for a small slab project; larger slabs justify scheduling delivery by a concrete company.

Position the cement mixer's outlet chute to pour the wet concrete into one end of the form. Begin the pouring. Use a shovel to push the concrete around and work it into all the nooks and crannies of the form.

Bear in mind that if you have to wade out in the concrete to work it, you really do need to wear your rubber boots. Concrete contains lye, and it's not too nice to your skin. Can you believe they used to put that stuff in soap? No wonder folks didn't bathe often.

Beginning the Concrete Finishing Process

After filling the form, level it with the edge of a 2" X 4". It should be long enough to overlap the form on both sides. Push and pull it in a sawing motion across the top of the form. Start at one end (your choice) and work it down to the opposite end. This process is called the "screed."

Apply the Darby

Now it's time to use the darby. I have absolutely no idea where this tool got its name, but you've got to admit, it sounds pretty cool! (Or is it just me?) The darby is a tool that smooths the surface of the concrete; it should be used on slabs small enough that you can reach everywhere by hand.

Larger projects such as a driveway, large patio, or a carport should be done with a bull float. The bull float is similar to the darby, and performs the same service, but it's outfitted with a pole so that you can work long-distance.

Whichever tool you use, use smooth, overlapping arcs. Push down while smoothing to remove lumps while filling any low spots. Take care not to work it too hard or the concrete will blister. Can you see where we're going with this? We're progressively fine-tuning the slab as it cures.

Next, wait until you see water beginning to appear on top of the slab. The time this takes to happen depends of factors such as humidity, etc. Next, you'll see that the water will reabsorb into the slab. Start testing the surface of the concrete. When your thumb, pressed into the surface of the concrete, leaves a quarter-of-an-inch deep impression, you'll know that it's time to edge and groove the concrete slab.

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