Pouring a Concrete Garage Floor

For any do-it-yourselfer, pouring a concrete garage floor is a huge undertaking and I highly recommend leaving it to a professional. But if you are serious, here are some things I think you should know before beginning.

First of all, finding some help from someone with experience in concrete will be a tremendous asset. Pouring and finishing concrete is a skilled trade. Because concrete is a perishable material, there's not much time for self training once the concrete arrives. If you screw it up, you're either stuck with it or shelling out big bucks to fix it.

The advice here assumes that the foundation and subgrade are in place and you're ready for the installation of the concrete floor. What the concrete floor will sit on is a whole other story that requires it's own set of instructions and advice. But do make sure that part of the project is completed correctly and the job is 100% ready for concrete when it shows up. You want to start pouring as soon as the concrete arrives. The concrete is getting hotter and hydrating as it spins in the drum. The sooner you get it out of the truck and on the ground, the more time you have to work with it.

Cover the subgrade with a layer of 4 or 6 mil visqueen. Plastic sheating creates a vapor barrier which prevents moisture from travelling up through the concrete. Your floor won't sweat and any sealers or coatings will adhere much longer.

Chalk lines on the walls where you want the top of the concrete. Normally, a garage floor should slope from back to front so water can't puddle too much. It can also slope to a drain in the middle.

Use the right mix for garage floors. A 4000 psi mix is ideal for most residential applications. The best thing to do is ask your local ready mix company for recommendations on a good mix design. Calculate the yardage and order 10% over the amount. It's better to have too much rather than not enough. Trust me!

Stretch a string line across the garage at the intended height of the concrete. Hammer wood stakes until the top of the stake is even with the string. These stakes are used as a guide for screeding. You need one placed about every 10 feet. A typical 20x20 garage needs one stake in the center.

Pour concrete along the walls first and float (smooth out) level with your chalk lines. This will also provide a guide for the screed.

Pour and screed the rest of the floor and smooth it out with a magnesium bullfloat.

It's important to understand that pouring a concrete garage floor is like riding a bike. I can explain it 'til I'm blue in the face, but you still won't know what you're doing. That's why I stress the point of having someone with experience to help.

Although a garage floor can be finished many ways, the best and most common method is a smooth trowel finish. It's quick, cheap, and easiest to keep clean and maintain.

Control joints for a garage should be cut the following day. Space them no more than 10 feet apart. The depth of the cut needs to be at least 1/4 of the slab thickness. So if the concrete is 4 inches thick, then the saw cuts should be at least 1 inch deep.

Pouring a concrete garage floor isn't nearly as easy as some make it seem. Please have some good help or pay a professional to do it.