So you want to make a patio for your backyard or is it a sidewalk around the side of your house. Maybe you want a pad for a new tool shed and you plan to make it using concrete. A good choice, concrete is durable, maintenance free and can have an attractive appearance. But it also cracks. Always.
Now I know what you're thinking, you've seen concrete that doesn't have any cracks. Somewhere. So how can I say 'all concrete cracks'? Concrete is made of cement, rock and sand, and when you add water it starts a chemical reaction that produces a hard material, which, when worked on, makes walkways, patios and driveways. However, as the concrete hardens, it shrinks and this shrinkage is responsible for almost all of the cracks you see in everyday concrete. So what to do. Ground preparation, reinforcing and control joints.
Before you place your concrete, make sure the ground is level and there are no soft areas. Soft places in the ground will cause your concrete to settle and crack. If you find any soft spots compact them with a hand compactor or you can rent a motorized one. The motorized compactors are superior, but for small areas a hand compactor will suffice. After compaction you may need to bring in some fill sand to re-level the surface. I find a sand and gravel mix, similar to road base, works best. Spread the sand around as needed to level the surface and you're almost ready for the concrete.
For reinforcing your concrete you have two choices, wiremesh or steel bars (rebar). Wiremesh comes two ways, in rolls and panels. The rolled wiremesh can be difficult to use and keep in place so I recommend using the panels. The panels can be cut to fit any size concrete pad and are easy to move around. You can also use rebar for reinforcement and, for most applications, I believe it to be the better (and easier) choice. Rebar is typically laid out in a checkerboard pattern on the ground. The bars are then tied together with wire.
After the rebar is tied off, it needs to be raised slightly off the ground so that it is in the middle of the concrete when the concrete is poured into your forms. To do this you can place small rocks, brick or pieces of of broken concrete under the rebar or you can buy plastic 'chairs' that the rebar will sit in to hold it in place. Rebar or wiremesh, if placed correctly, will keep your sidewalk or patio together should any cracks develop. Your ground is ready, the reinforcing securely positioned and as many friend as you could bribe with beer on hand to help with the concrete. When the concrete truck arrives, wet the ground inside your patio or sidewalk forms. Doing this will keep the water in the concrete you are pouring from being absorbed too quickly into the ground. Once the concrete has been poured, make sure to protect it from wind and, on a hot day, direct sunlight. Both or either can cause the concrete to dry too quickly, which will result in unsightly random cracking.
Your friends are gone, the beer too, but there's still one thing left to do to help control cracking. Control joints or contraction joints. You see them everywhere. A slab of concrete is seldom done without a control joint. Remember, all concrete cracks, so what you want to do is control where the crack happens and how it looks. Control joints can be tooled in with a special tool know as a joiner or sawed in after the concrete has set up by using a concrete saw.
If your sidewalk or patio is four inches thick (and most are) then the depth of the joint should be 3/4 to one inch deep into the concrete. Where to put them will vary depending upon the size of your pad. In a 4 x 50 foot sidewalk you would want them evenly spaced every 4 - 6 feet. A 10 x 10 patio doesn't require a control joint (10 x 10 is almost the perfect size for any concrete pad and usually has no problem with cracks), but a 10 x 20 patio should have one control joint at the half way point of the 20 foot length. A rule of thumb. Any time the concrete approaches twice as long as it is wide, it needs a control joint.
Follow the above recommendations and you will have a concrete pad that will be durable and attractive.
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