Are you planning to build a small patio or maybe a spot for an outdoor fireplace, but don’t know where to begin? This guide will show you how to pour a small concrete slab as clearly I can explain so you can succeed in it on the first try. If you have a bigger project, here is a guide for how to pour a concrete patio.
Pouring a concrete slab is a labor-intensive job. It also requires some skill and good advice if you’ve never done it before. When you know the possible failures, succeeding is so much easier.
Before you pour the concrete, you need to prep the slab first. In this article, I’ll show you the basics from beginning to end and give you some inside tips to make your concrete slab-pouring job as easy as possible.
Before you begin
When you begin prepping a slab the first thing you need to consider is the placement. Where is the best possible area? Is the ground level? Will water run onto the slab? All of these questions need to be addressed before you break ground.
Building a concrete slab isn’t all that difficult, though, to be honest. You’ll need to invest in some tools before you start, including a concrete float, a trowel, wheelbarrow, and a garden hoe, as well as a curbing trowel and a tool that allows you to form the stress relief joints in the concrete.
Make a level ground for the form
The most important aspect of installing a concrete slab patio on your home is to make certain that the ground underneath the patio is flat and level before you pour the concrete. If you avoid this step, it will lead to cracks in the concrete and may make it necessary to remove the existing pad and replace it with a freshly poured patio, effectively doubling your expenses for the project, in addition to adding the disposal fee for getting rid of the broken concrete.
Rent a builders level from your local rental place before you begin. This will tell you how to level the ground is, where the slopes lie, and any dips or mounds in the ground. Set up the level and have a friend go around the perimeter with the level as you check the height. A laser level is the preferred choice and can be worked solo.
Mark the area around the slab
Start from the highest area and place a stake or flag into the ground. This should be your corner. Measure the appropriate length and width of the slab. To ensure a square slab, measure from corner to corner.
Adjust the stakes on each opposite corner until the measurement is the same. If you move one, you must move the opposite stake or flag the same distance. Once you are satisfied your corner-to-corner measurements are the same, double-check the lengths and widths to ensure your measurements are correct.
Excavating the ground
Begin by excavating the area where the concrete slab will be installed. You’ll need to dig down at least 12 inches for smaller slabs, such as those that measure no more than five by ten feet, but for patios that are any larger, a depth of 18 inches is a good idea. This allows you to add additional paver base sand to the excavation and prevent problems with the concrete cracking.
Fill the ground with gravel and sand
Fill the base of the excavation with no less than six inches of paver base gravel. If you have an 18-inch deep excavation, use ten inches of paver base gravel. At this point, you’ll need a soil compactor. These tools are widely available for rental. The machine works by jumping up and down on the paver base, packing and leveling the material until it is tightly pressed into place.
Fill the excavation with 4 inches of paver base sand. The paver base sand then needs to be packed into place with the soil compactor, as well.
How to build wood concrete forms
When the paver base is in position, you can now place the four form boards you’ll need to make certain that the edges of the concrete slab are straight and true. For your success, this is the most important step now so I’ll go more into details. For more about this subject, read here about forming and also this article for forming and texture.
Properly build strong form can hold the concrete within with ease and is also set level so all you need to do is screed the concrete and float it smooth. Take some extra time with this and the pour will go smoothly. Here are some concrete forming tips:
Step 1: First set up your batter boards. These are boards that are placed around each flag or stake. It will form a rough corner on each corner. Use the laser level to make the batter boards the same height as the highest part of your slab.
Step 2: Make a mark on each stake and transfer it to the batter boards using a level or the laser level. Attach the batter boards with a few duplex nails.
Step 3: Once marking is done, you will need to redo the slabs measurements on the top of the batter boards. Measure each length and width accurately.
Place a nail in the top of the batter boards. String a line along the perimeter attaching it to each nail.
Now do a cross corner measurement as you did previously. Adjust the string and nails accordingly, until you have a square slab with the correct length and widths.
Step 4: Now that you have square form, you can begin to place the form boards.
Set the form boards flush with the strings. Drive stakes into the backside of the form boards and attach them with duplex nails.
Use a sledgehammer to hold the form boards from bouncing. Continue around the perimeter of the slab holding each form to the strings height and sides.
Step 5: Next grade the slab using a rake and shovel. Pull a string across the forms and measure down until you have reached the desired thickness of your slab.
Use a long straight edge to grade the dirt evenly. Dig any footers and finish grading the slab.
Place plastic down along the entire bottom of the slab. Place any rebar on the form as needed at this time. You are now ready to pour the concrete into the forms for your concrete slab.
Mixing the concrete for the slab
Mix the concrete with water until it is of a slightly thinner consistency than peanut butter. This will give you additional time to float and form the concrete before it begins to set. Follow the manufacturer info on the water and concrete ratio and you should be fine. Use a wheelbarrow to mix the concrete, and then pour the concrete into the excavation.
Now I know this is about how to pour a small concrete slab, but even something considered small might need a lot of mixing of the concrete. For that reason, I recommend setting the mixing spot near the slab so you can effectively work on wet concrete.
Step 1: Mix the concrete and pour it in the back end of the slab. Pour enough to have 1-2 feet length to screed.
Step 2: Vibrate the concrete you have poured to help some of the air in it to escape, then screed it level using the side of the forms to “saw” it with level or 2×4 or whatever you are using to screed.
Step 3: Repeat step 1 and 2 until you have whole form full of concrete. This is pretty much pouring concrete in two stages, pour and screed.
Step 4: Float the surface when you have poured and screeded the whole slab. With small slab it should be OK to do it like this.
When the surface is adequately flattened, you will then be able to add the stress relief channels into the patio surface if needed. These channels should be positioned every eight feet. If you want to know more about finishing concrete, read the link.
This means that they are not necessary on smaller slabs, but are necessary on larger ones. If your slab falls in between add them.
They provide a place for the concrete to crack where it isn’t obtrusive.
After the stress relief channels are in place, use the curbing trowel to round off the sides of the patio, and then allow it to cure for at least a week before walking on it.
After the concrete has fully cured after 4 weeks, you can backfill the dirt around the sides of the patio slab. You can remove the forms when you feel confident it has cured enough. If you don’t know, let them be for the whole 4 weeks.
If you’re water curing the concrete, remember to water it and use some sort of canvas to stop the water from evaporating if you’re doing this in hot season.
Concrete that is water cured is 50% stronger than one that is not so you should really do it or use some alternative method. Depending on the use of slab, its not much trouble so I usually say it should be done no matter what.
You should know how to pour a small concrete slab now. As a process it’s not that complicated, but you need to carefully prepare to succeed.
Make sure your ground is flat. After that you need to make a good and level form for the concrete. When all that is done, it’s just a matter of mixing concrete and pouring it.
With small slab, everyone should be able to do it if you take your time.