How Thick Should Concrete Patio Slab Be
So, youre planning to pour a new concrete patio to expand your backyard landscape and get a little more room to grill. Before you start, you need to know the right thickness for the patio. If you get it wrong, youll either spend far too much time and money on a thick patio or waste your money on a crumbling patio that doesnt meet code! So, how thick should a concrete patio be?
Most concrete patios, and other concrete slabs, are 4 inches thick. Building codes across the country usually require a thickness of 3.5 inches and compressive strength of 3,000 PSI. However, many things determine whether a concrete patio should be thicker, or incorporate rebar/reinforcement mesh.
In this article, youll learn how thick a concrete patio should be, the factors and building codes that determine the right slab thickness, and the basic steps of pouring your own concrete patio.
How To Pour A Concrete Patio
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Patios can be wonderful additions to any home, but homeowners generally have to weigh the benefits of having a patio with the expense of having someone do the construction. To save on this expense, however, consider making a concrete patio one of your next do-it-yourself projects.
Tips For Building A Concrete Patio
Buying concrete in dry, premixed bags makes sense for relatively small patio slabs. To get an idea of how many bags you would need, a 50-square-foot slab at 4 inches thick needs about 28 80-pound bags or 38 60-pound bags. You can buy bagged concrete a local home center or lumberyard, and you can rent a concrete mixer at any large rental outlet.
For large slabs, consider ordering ready-mix concrete delivered by a concrete truck. Ready-mix is more expensive than bagged concrete, but it’s far more convenient, and you don’t have the labor of mixing the concrete or the concern of getting the mix just right. Discuss your plans with local concrete companies to compare costs and to make sure your site is suitable for ready-mix delivery.
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Not Having The Right Amount Of Concrete
Another mistake homeowners make when pouring a concrete patio is underestimating how thick the slab needs to be. To make sure safety is maintained, a minimum thickness of any concrete patio is at least 4 inches. However, if it will bear heavy furniture or features, 6- to 8-inch thickness may be required. This is in addition to a 2- to 3-inch base of something like gravel, sand, or limestone.
In the end, you only get one pour. Err on the side of caution and order slightly more than enough. If you have extra bags, you can always return them.
Not Being Properly Prepared
The most common issue do-it-yourselfers have when pouring concrete is not being thoroughly prepared. The process takes a lot more than getting the shovel out of the shed and clearing a spot. How ready that spot is to receive a ton of concrete determines everything.
Inexperienced DIY-ers tend to overlook many thingssuch as failing to use a plate compactor to pack the soil, not leveling the area adequately, or not setting up proper formsthe blocking that allows for a smooth, even pour. There are a lot of steps to pouring concrete property.
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Diy Concrete Patio Step Two: Building The Frame
Follow the level string and pound your pegs into the ground. Make sure they are as secure as possible. Also, make sure the tops of all the pegs are level to each other.
Take your boards and nail them to the pegs on the inside keeping the tops of the boards flush with the tops of the pegs.
You want your frame to be as secure as possible. Freshly poured concrete can push on the boards and bow your frame, leaving you with uneven edges that are almost impossible to fix.
So, it is best to place kickers behind the pegs. Kickers are pegs placed at a diagonal against your vertical pegs and nailed through your boards.
Before the next step, take a minute to double-check everything is level and ready to add gravel.
Dampen The Base To Lengthen Finish Time
To extend your finish time on hot, sunny days, spray bone-dry ground with water to keep the base from sucking the water out of the concrete. A water spray also slows down curing, which makes for a stronger slab. If theres no hose bib nearby, you can use the water and hose that are onboard the truck. If you dont have water on site, also use the truck hose to fill a couple buckets of water for cleaning your tools after the truck leaves.
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Stake And Brace The Side Form
- Stretch a mason’s line just above the top edge of the 2×12.
- Align the 2×12 with the string and brace it with pairs of 2x4s spaced every two feet.
- To absorb the shock and make nailing easier, hold a sledgehammer behind stakes and form boards as you nail.
- Brace the forms to ensure straight sides. Freshly poured concrete can push form boards outward, leaving your slab with a curved edge that’s almost impossible to fix. The best way to avoid this is with extra strong bracing. Place 2×4 stakes and 2×4 kickers every two feet along the form boards for support. Kickers slant down into the ground and keep the top of the stakes from bending outward.
Setting Up Slab Perimeter
Measure the perimeter of the area to pour the concrete over the existing slab. Depending upon the requirement of the preferred use of the slab and the loads coming upon the slab. The thickness of the slab is designed. The measurements acquired can then be used to estimate the amount of concrete required.
- Calculation of Sizes of concrete.
- Installation of Wodden braces and Reinforcement mesh over-existing concrete.
The braces are installed around the area to be filled with concrete usually made of wood. It must be ensured that the braces are evenly spread which is can be done by running a bubble or string. For the thick concrete slab, a wire-mesh is needed on the braces to provide strength.
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Secure The First Form Board
Drive a stake into the ground at each corner of the slab area. Cut one side of the form to length and nail it to a corner stake. Level the board and nail it to the second corner stake. Stretch a masons line just above the top edge of the board, align the board with the string and brace it with pairs of 2x4s every 2 ft. To absorb the shock and make nailing easier, hold a sledgehammer behind the stakes and form boards as you nail.
Lay Out The Rebar Grid
Cut and bend pieces of rebar to form the perimeter reinforcing. Splice the pieces together by overlapping them at least 6 in. and wrapping tie wire around the overlap. Wire the perimeter rebar to rebar stakes for support. Then cut and lay out pieces in a 4-ft.-on-center grid pattern. Wire the intersections together. Youll pull the grid up into the center of the concrete as you pour the slab.
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Not Knowing The Type Of Concrete You Need
There are literally thousands of types of concrete. What kind will you use to pour your patio? Its all the same, right? Not really.
You might decide to pick up some quick-setting cement, low-heat cement, or sulfates-resisting cement. Should it be blast furnace slag, high alumina, or air entraining? These are just a few kinds of cement that serve different purposes. Whatever you choose, a strength of 4,000-4,500 psi after a one-month cure is an important feature to keep in mind.
Pouring Concrete Patio: What Could Go Wrong With Doing It Yourself
So, youre ready to make this summer the year of outdoor fun in your backyard, and youve got a new concrete patio on your mind. Before you pour the concrete yourself, keep in mind there are practical, aesthetic, and safety concerns that come with any DIY concrete project.
The fact is, pouring concrete requires a good deal more knowledge and skill than other home exterior projects. Doing it right demands careful planning, as well as the proper materials and tools to avoid weakened concrete and an inevitable do-over. There are a number of things you need to carefully avoid in order to stay safe and prevent a DIY disaster.
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How To Broom Finish And Seal The Concrete
Knowing how and when to start the finishing process is one of the hardest things to learn about concrete finishing.
In the video below, I will show you how we start the finishing process and apply a broom finish to the concrete.
The finishing is always determined by how fast of slow the concrete sets up. I’ll show you the best time to start finishing in the video below for best results.
I used a penetrating sealer to seal the concrete with in the video. This type of sealer will not leave a slippery film on the surface but will seal and protect your concrete.
It’s best applied with some type of sprayer. We’re using a power sprayer in the video but you can use a simple garden pump up style sprayer if you like.
tools you’ll need to build a concrete patio slab
I’ve made a list of all the tools you’ll need to build your concrete patio slab.
Most of these you can get at your local hardware store or even easier, you can order them right from Amazon.
I built this page to help you decide if you want to pour your own concrete patio or not.
If you kind of handy and like building and doing things on your own, then maybe it’s something you can tackle by yourself after watching my videos.
If the size of your patio slab isn’t too large, maybe you can do it yourself with the information I’ve given you on this page.
If you have any doubts or questions, then look to hire a pro like me. We do this kind of work every day.
Fewer Years Of Service
A well-poured concrete slab with a deep, sturdy foundation can last for 30 to 40 years. Pouring concrete over old concrete instead of directly over a new gravel foundation limits your ability to maximize the slab’s lifespan.
The condition of the existing slab is the primary factor that determines how long the new concrete will last. If the foundation beneath the slab is not sound, the new concrete could sink or develop deep potholes.
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Thicknesses For Different Types Of Poured Concrete
Different types of concrete slabs can require different slab thicknesses. Here are the standard slab thicknesses of different residential concrete slabs:
- PatiosThe normal thickness of a concrete slab on grade is four inches sometimes they are thicker if the building situation requires that they be.
- Slab FoundationHouses built on concrete slabs are between 4 and 6 inches thick and are reinforced with steel mesh or rebar.
- Basement FoundationsThe basement pad doesnt support the weight of the home, so the basement floor is usually 3.5 inches thick.
- DrivewaysThe standard slab thickness for a driveway is 4 inches. This gives the driveway the compressive strength to support the weight of average-sized cars. Driveways that hold commercial vehicles or mobile homes should be thicker.
- SidewalksA four-inch slab is the norm. The big difference is that concrete used to pour sidewalks neednt be rated for the same strength, so is cheaper to buy. However, some builders opt to pour a 3-inch slab using heavier-duty concrete.
Concrete Slab On Grade
Slab on grade refers to a concrete slab that’s used as a foundation for a structure. The slab is created from a mold built into the ground thats reinforced with rebar and wire mesh. The frame is constructed from wood, and the concrete and aggregate are poured into the mold to harden.
The three types of concrete slab on grade are:
- Slab on the ground slab with concrete beams around the perimeter
- Stiffened raft slab slab with concrete beams set in a grid throughout the slab
- Waffle raft slab above ground slab poured over polystyrene void forms.
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How Much Concrete Do I Need
Once this preparation is complete, you are ready to lay your concrete slab. To help you determine how much concrete you need we have developed an easy-to-use online concrete calculator. It asks for the basic shape of the area you are working with square/rectangle, right-angled triangles, parts of a circle and dimensions to provide you with an estimate of the volume you require. If you’ve got a complicated area to estimate, you can build up the calculation by adding the different shapes together.
What Determines Whether Or Not You Reinforce Concrete
There are pours that will require reinforcement in concrete, but many situations are left up to your judgment. If you decide youd like the added strength and expense, good if not, no worries. Here are some situations where reinforcing the concrete slab is either required or recommended:
If the concrete slab thickness is greater than 5 inches, it is a good idea to use rebar or at least wire reinforcement mesh. It is required in some building codes. Before pouring a slab thicker than five inches, consult your state and local building codes!
If the concrete slab is supporting the weight of a hot tub or building, wire mesh and rebar can be required by local building codes.
Beams and columns made from concrete will usually require rebar to function properly and safely.
Slab on Slope
When pouring on a slope, in addition to pouring thicker on the lower part of the slope, it is a good idea to use wire mesh to add tensile strength to the slab. This will prevent cracking due to uneven weight placement and shifting soil.
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Install The Gravel Base
Fill the excavated area with 2 inches of compactible gravel. Rake the gravel smooth, then compact it thoroughly with the plate compactor. Add 2 more inches of gravel, and rake it smooth. Measure down from the layout strings and use the 2×4 with a carpenter’s level on top to make sure the gravel is level side-to-side and slopes end-to-end to follow the strings. Compact the second layer of gravel.
Using The Wrong Tools
Strong, heavy-duty tools are absolutely a must when working with concrete. Using the wrong tools results in a shoddy-looking concrete slab.
Before mixing the concrete, have these tools ready: a pressure washer, safety goggles, a large wheelbarrow, an electric concrete mixer, a bull float to flatten the surface, a magnesium float for bumps, tools to create the concrete form, a broom, a brush, an edger, a finishing trowel, gloves and buckets.
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Setting Up A Slab Perimeter
How To Determine The Correct Thickness Of Concrete Slab
To determine the correct thickness of a patio slab and how much it can support isnt quite as simple as a number. Proper slab thickness is determined by:
- Compressive strength
- Tensile strength, affected by the presence or lack of reinforcement
- What is being placed on the patio
- The weight of the concrete slab itself
- The size of the pad in square feet
The main concerns are the compressive strength, presence of reinforcement, and the surface area of the patio. If your patio is going to be supporting a lot of weight, increase the thickness, or use high-strength concrete with a rating of 5-6,000 PSI.
Additionally, it is advisable to use reinforcing mesh or rebar if your patio will be supporting heavy loads or will be built on uneven ground. This will give it the tensile strength it needs to support varying amounts of pressure across different points of the slab without breaking.
For a concrete patio, the ideal slab thickness is at least four inches. There are times where thicker slabs will make more sense, but, most of the time, 4 inches is the perfect thickness for a concrete slab. It is, however, wise to make the perimeter of the slab an inch or two thicker. This will help the slab withstand soil erosion and cracking.
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