November 3, 2023
Forming a concrete slab is something you can do yourself. Learning how to form a concrete slab will be easy if you follow my step by step instructions.
I've formed over a thousand concrete slabs in the 30 years that I've been doing concrete work. There are many ways to form a garage slab or form a house slab. We've found a way that's simple, fast, efficient, and gets the job done.
The tools you'll need for forming a concrete slab are: Hammer, nails, tape measure, string, pencil, stakes, laser level.
Optional: Dewalt drill driver and 2.5" deck screws - We like these better than a hammer an nails for fastening the forms together. It's also easier to strip the forms when the slab pour is done.
Let's say for example we're forming a garage slab that is 26 feet
wide by 26 feet long by 6 inches thick. We would use 2x6's for this, if
the edges are thicker just use a bigger board for however thick the
edge ends up being.
1. The first thing I do is make sure the sub-grade is level. If it's not level you're going to have to dig some boards down and lift some boards up. The best way to form a concrete slab is to make sure the dirt is level before you start.
This gravel pad is level to within an inch. That's close enough to form a concrete slab without any problems.
2. The next step is to lay out your boards for each side. The boards need to be at least 1.5 inches longer than each side so you have something to nail them together with. (26 ft 1 1/2" long)
3. I like to use a board at least 2 - 4 feet long to nail the two side boards together. This will help give the side some strength where the longer boards butt together.
4. After all the sides are nailed together, stand them up on edge. Start with one side and measure the exact length (26 ft in our example).
Mark the board with a pencil at your measurement. Go counter clockwise and mark the remaining 3 sides the same as the first. (All ours are 26 feet in this example)
5. When your done marking the boards, you can nail them together using the pencil marks you just made. Since you made each side at least 1 1/2 inches longer, you have plenty of board to easily nail them together.
6. One of the most important steps to forming a concrete slab is squaring it. After the four sides are nailed together, straighten them by eye the best you can. Then use a tape measure and measure diagonally from corner to corner. you should get the same measurement.
If you don't, adjust (slide) the boards one way or the other until you get the same measurement both ways. When you have the exact same distance from corner to corner (diagonally), the forms are perfectly square.
7. When the forms are square, we pin the corners with some metal stakes to hold them in place. You can use wooden stakes if that is what you have. After we've staked the four corners we double check for square.
8. Once the slab is square we pound a nail in each corner and run a string around the perimeter of the slab forms. We use the string to straighten the forms while we stake the rest of the boards. Hammer a stake about every 4 to 5 feet to keep the forms straight when you pour the concrete for the slab.
9. When all the boards are staked in place, we use a laser level to set the boards to grade. Start at one corner and work yourself around the slab until you get back to where you started.
Forming a concrete slab is really quite easy if you have a plan to go by. It takes us about a half hour to form a concrete slab this size.
If you're forming a garage slab or a house slab, the steps are basically the same. Sometimes all four sides aren't exactly the same length, a 30 ft. by 24 ft. slab is done the same way.
Another tip when you're learning how to form a concrete slab is to use straight form boards. Straight boards are much easier to nail, plumb, and square. Using this guide to forming a concrete slab will help you get it done right.
If you want to see how we pour a concrete slab click on POURING A CONCRETE SLAB.
If you need a little more help, or have some doubts or questions still unanswered, then I can help you with that.
I created a Concrete Slab Course that teaches you everything I know about forming and pouring a concrete slab.
This course will answer all your questions and erase any doubts you have about doing this yourself.
I cover, in depth, exactly how we form all our concrete slabs to prepare it for the pour, and I walk you through how we pour the concrete for the slab the same way we do it. All in video format for easy learning.
The cost of the course is only $49.00. But it will save you hundreds, maybe thousands of dollars versus hiring a professional to install your slab for you.
If you buy the course and it doesn't help you or it doesn't teach you anything. Just let me know in the first 30 days and I'll refund all your money. No questions asked!
You can check it out HERE!