Pouring the Best Concrete Garage Floor
You garage floor has to support heavy vehicles, and withstand harmful chemicals like de-icers, gasoline, and motor oil on a daily basis. It also has to endure heat/thaw conditions, which means that the concrete is constantly expanding and shrinking. This can result in cracking, flaking, and ultimately the deterioration of your concrete floor. To help protect your garage floor it's very important that you install it properly.
There are several different things that you want to consider when pouring your concrete floor:
Start with a Good Base
A good base is an important pre-condition for pouring a new concrete garage floor. It must be able to:
support 125 pounds of pressure per square foot
provide consistent support
If the base soil doesn't provide consistent support the concrete will settle unevenly, which will lead to bending and cracking. To avoid this you need to make sure that all of the soil has been compacted. The best way to compact the soil is to remove the topsoil and replace it with at least 4 inches of compactible, irregularly shaped gravel. This will let water escape, helps spread the load over the soil, and will keep your concrete thickness equal.
Use a Vapor Barrier
Moisture in the ground will eventually rise up into the concrete slabs and condense underneath anything that is on top of the concrete (i.e. storage boxes, cars, etc.). You will be able to tell that this is happening if you have dark spots in your concrete. Not only is this not aesthetically pleasing, but it can result in delamination of your floor's coating and slab "sweating", which is when moisture accumulates on top of of the concrete slab increasing its slipperiness and making it dangerous. Vapor barriers are a cheap way of preventing this from happening.
Don't Add Water!
Sometimes it might be tempting to add water to the concrete mix because it will seem dry and stiff. Do not give into this temptation, because the more water there is in the mix the weaker the concrete will be. In colder climates it's extremely important that concrete is strong to prevent it from cracking and breaking. If your cement mix is truly too dry to mix or pour, consider using super-plasticizers instead of water. Adding these to your mix will push the cement grains apart, making it flow more easily.
Using air-entrained concrete is essential if you live in a climate that experiences freezing temperatures. Air-entrained concrete is created by adding a soaplike admixture that froths and produces billions of microscopic air bubbles. These bubbles are extremely important in preventing your concrete from cracking and flaking in extreme temperatures. Essentially, these air bubbles relieve pressure in the concrete by providing chambers for water to expand in when it freezes, as opposed to expanding in the concrete, thus causing cracking and flaking. If you don't know how to do this yourself be sure to use a trusted concrete producer who will adjust your mix accordingly.
Isolate Each Slab of Concrete
As previously mentioned, concrete slabs continue to expand and contract with changes in temperature, which can make them prone to cracking and flaking. To help avoid this from happening it's important that you use isolation joints around the perimeter of each concrete slab. This helps the concrete move independently and prevents cracking.
Don't Rush the Process
If your concrete dries too quickly it will crack and shrink, and might curl upward at the edges. To prevent this from happening you can spray a membrane-forming curing compound on the surface of the concrete. This membrane will trap moisture in the concrete, preventing it from drying out quickly. You can also use poly sheeting or curing blankets that also trap the moisture in the concrete but don't interfere with adhesion like curing compounds can.