A concrete slab is an essential structural element of almost any building. Whether you’re building a house, barndominium, garage, or workshop, you will need a concrete slab at some point in your construction project. What are concrete slabs, and why are they so important?
This article discusses concrete slabs, why you need them, and how much they cost. We will also guide you on how to build a durable concrete slab for your property and answer some questions you might have about them.
Table of Contents
- 1 What is a Concrete Slab?
- 2 What’s the Difference Between Cement and Concrete Slabs?
- 3 Why Install a Concrete Slab?
- 4 How Much Does It Cost to Install a Concrete Slab?
- 5 What are the Different Types of Concrete Slabs?
- 6 How to Pour a Concrete Slab
- 7 Things to Ask Your Contractor About Concrete Slabs
- 8 Should You DIY or Hire a Professional for Your Concrete Slab Installation?
- 9 Final Thoughts
What is a Concrete Slab?
A concrete slab is a flat, horizontal surface often used as a floor or roof. As its name suggests, it is made of cast concrete. The main purpose of a concrete slab is to add structure to a building. Examples of concrete slabs include basketball courts, floors, patios, and driveways. Although most concrete slabs have a uniform thickness, some have a variable thickness.
What’s the Difference Between Cement and Concrete Slabs?
You’ll often hear the terms cement and concrete used interchangeably, but they are not the same. Cement is a chemical substance used in construction and is an ingredient of concrete. When cement sets, hardens, and dries, it adheres to other building materials and binds them together. Concrete is a composite material made of cement, water, and fine and coarse aggregate, like sand and gravel. All these materials bond together with the help of cement.
Why Install a Concrete Slab?
So, what makes concrete slabs so important, and why are they so popular in construction? Let’s dive in and take a closer look at some of the benefits and drawbacks of concrete slabs.
- Less time to dry – Concrete slabs take less time to dry. You can pour the concrete slab in one day, and it will dry within 24 to 48 hours. Although the concrete will be dry enough for you to walk on after 48 hours, full curing will take up to 28 days. Since it dries faster, expect less downtime, and your construction project can proceed without delay. If you are building in an area that experiences frequent inclement weather, a shorter construction time can help you avoid harsh weather conditions that might delay the completion of your structure.
- Cost-efficient – A concrete slab foundation is cost-efficient for most homeowners. A house built on a concrete slab is cheaper to build.
Opting for a concrete slab can also help you save money in other ways. For one, since it is faster than building a basement, you can save on labor expenses. If you rent while waiting for your house to be built, a shorter construction time can help you save on rental expenses.
Slabs are also excellent insulators. This can help you save money since you can keep your cooling and heating bills low.
- Easier to maintain – A concrete slab is easy to maintain. With proper maintenance, you can extend the life of a concrete slab and keep it looking great. You can clean a concrete slab at least once a year to get rid of dirt and prevent the build-up of grime. However, choose a cleaner specifically made for concrete, as some household cleaning chemicals can damage concrete. Be sure to read the instructions on the label of your detergent to determine the proper way of using it.
It is also best to remove stains as soon as you see them to ensure that they don’t cause discoloration or staining. Although a concrete sealer can help protect a slab from stains, removing spills or stains as soon as possible is still the best preventive method.
- Can help reduce damage from flooding – A concrete slab foundation acts as a moisture barrier to protect the interior of your house from damage resulting from flooding. In contrast, basement foundations are notoriously prone to flooding, especially if they are not properly sealed.
- Can help deter pests – A concrete slab foundation is less prone to infestation of pests, like termites and rodents. This is because, unlike houses with basements or crawl spaces, there are no open spaces beneath your concrete slab where pests can live. Yes, pests can still get into your house through other means, but you don’t need to worry about finding termite or wasp nests in your crawl space or a nest of rodents in your basement.
- Slabs can crack – Concrete slabs are not perfect, and one of the most common issues is homeowners finding cracks on their concrete slabs. Hairline cracks are normal and may result from shrinkage as the concrete hardens or dries.
While hairline cracks are normal, large cracks are not. Large cracks can compromise the structural integrity of a building and put its occupants in danger. Large cracks on a concrete slab can result from soil shifting, earthquakes, frozen ground, or tree roots. If you want to prevent slab cracks, make sure you don’t plant trees too close to your house since their roots can damage a concrete slab foundation or walkway.
Preventing soil displacement is another way to prevent slab cracks. Soil displacement is common in areas with loose soil and locations that experience frequent flooding. One of the ways to minimize soil displacement is by ensuring that your landscaping directs water away from your house. This will help prevent floodwater from accumulating around and under your house, resulting in soil displacement.
Another way of preventing cracks from developing is by maintaining a constant temperature inside your house. Extreme changes in temperature can cause your concrete slab to expand and contract, leading to cracks developing.
- Reduced storage options – One of the benefits of having a basement foundation is the amount of extra space it offers. You can use the additional space as a storage area for seldom-used items. This can help you un-clutter your house. You can also use your basement as your laundry area or convert it into an extra bedroom, a media room, a home gym, etc. If you go for a concrete slab foundation without a basement, you are closing the possibility of having additional space underneath your home.
- Utilities installation – If you have a concrete slab foundation, you need to install your HVAC system above ground. Having your HVAC system above ground will eat up floor space, giving you a smaller usable square footage for your living spaces.
A concrete slab foundation will also force you to have your water and gas lines embedded in the foundation. This is because there’s no space for you to run your gas and water line underneath your floor. You’ll be forced to open your foundation if something goes wrong, and you need to replace your gas or water pipes; this can be expensive. The repairs will also take longer to complete and cause inconvenience to your family.
How Much Does It Cost to Install a Concrete Slab?
Installing a concrete slab ranges between $4 and $8 per square foot. This estimate includes the cost of materials and labor costs. However, the cost of a new concrete slab depends on its size and thickness. Price estimates also depend on the prevailing inflation rate that affects the cost of building materials like cement, gravel, and sand. It will also depend on your location and the builder you are working with. Read our cost of concrete slab article for a more detailed discussion.
What are the Different Types of Concrete Slabs?
There are different types of concrete slabs, and knowing about them can help you decide what you need. It will also help you understand the costs associated with building them. We are not tackling all but concentrating on the most common and simplest types.
Slab on Grade
A type of concrete slab poured and cast on the earth’s surface. It is also called a ground slab. Slab-on-grade has three subtypes, and each has its own advantages.
Slab-on-ground – This is the simplest type of slab-on-grade. It got its name because all, or a part, of the concrete slab, is resting or in direct contact with the ground beneath it.
T-Shaped – This type of concrete slab is more complicated than a slab on grade and is recommended for those living where the ground freezes during winter. Building a T-shaped concrete slab requires setting inverted t-shaped feet into the ground. Walls are then built on top of these feet to create a frame. Builders then pour a concrete mixture into the created frame to create a concrete slab.
Aside from helping improve structural integrity, a T-shaped concrete slab also offers better support for load-bearing walls. If you plan on building a multi-story structure, a T-shaped concrete slab foundation might be a better choice since it can help support the weight of the additional stories. However, because they are more complicated and take longer to finish than slab-on-grade foundations, T-shaped slab foundations are also more expensive.
Frost Protected – A frost-protected foundation is similar to a t-shaped concrete slab because it also protects structures in cold climates from the damaging effects of frost heaves. This type of concrete slab foundation originated from Scandinavia, where some countries, like Finland, have to contend with sub-arctic climates. Builders use polystyrene sheets to insulate the edges of the concrete slab and the ground surrounding the foundation walls. This results in raised frost levels and lower risks of frost heave.
Unlike t-shaped foundations, frost-protected foundations have shallower depths. This makes them easier to build. They also require fewer building materials. All these factors make frost-protected foundations cheaper alternatives than T-shaped concrete foundations.
How to Pour a Concrete Slab
If you are doing a DIY build, it helps to know how to perform tasks that you would otherwise outsource to professionals. Aside from saving money on labor expenses, you gain new skills for future construction projects. If you decide to hire a contractor to pour your concrete slab, you can use this section as a guide to see if the contractor is doing anything different.
Things You’ll Need
- Concrete mix
- Forming lumber
- Packable fill
- Mixing hoe
- One-bag cement mixer
- Concrete broom
- Hand float
- Knee boards
Clear the area of rocks, grass, and other debris. You need to do this until you have bare earth exposed. If the ground is very compact and stable, you can proceed to the next step. If the ground is loose, place and compact a sub-base made of fill gravel. If you are in Texas, we recommend a reputable gravel & sand supplier in Waco, that also serves Austin and Bryan areas.
Create a form made of wood. A wood form can be made from wooden boards held together by screws or nails. Ensure that the screws or nails are easy to remove once the concrete slab is set. The form is where you will pour your cement mix, so make sure that the size of the form corresponds to the size of the slab you are making. Place the wood form in the area where you are making the concrete slab. You can use metal or wood stakes to stabilize the wood form.
Mix your concrete according to the directions on the packaging. You can use a one-bag mixer to make the task easier. You can use a shovel and wheelbarrow if you don’t have a mixer. If you are getting wet concrete delivered, the drum on the back of the truck should constantly be spinning to prevent concrete from settling and getting hard.
Pour the concrete into the wood form until it is filled to the brim. As the concrete mixture is being poured, you can use a rake or shovel to move the concrete around. This will help ensure that there are no air pockets or voids that can result in honeycombing.
Using a large metal or wood board, screed the top of the concrete slab. Screeding can help remove excess concrete and bring the concrete slab’s surface to the proper grade. This can also help ensure that the concrete is compact. If you don’t own a screed, you can use a straight board as a makeshift screed. You can use a hand float, darby, or bull float to even the top of the slab to have a smoother finish. This step also helps remove excess or bleed water from your concrete slab.
Allow the concrete to rest and wait until the surface becomes a bit firm. Do not start this step if you still see excess or bleed water on the concrete slab’s surface. You can then use a trowel to ensure a smooth and uniform finish. You can trowel by “skating” across the concrete slab’s surface on knee boards and troweling small areas at a time. An alternative is to use tools on long poles known as fresnos or funny trowels. If you are after a rough broom finish, there is no need to trowel the concrete slab. The other types of concrete finishes, like stained, stamped, exposed aggregates, and stenciled, are a bit more complicated, and it is best to leave them in the hands of experts.
Apply the final finish to your concrete slab. You can have a smooth, stamped, or textured finish depending on where you will use the concrete slab. Use a concrete broom to give the slab a rough textured surface or a broom finish for a rough finish. This type of finish can be coarse or light, depending on the bristles of the concrete broom you will use. Although a broom finish is not much to look at, it results in a non-slip surface. You can use a broom finish for a concrete slab that will constantly be wet, like garden walkways or those surrounding a swimming pool.
Although trowel finishes are often smooth, there are ways to give them some texture. Using a wood float can give the concrete slab a coarser texture. You can use steel trowels or aluminum floats if you want a medium or smooth finish. You can also give your concrete slab a pattern of swirls or arcs to give it a bit of character. Search for instructional videos on creating patterns on concrete if you are interested in patterned concrete.
Allow the concrete to rest and cure. The curing process should take 28 days. You can use a liquid chemical curing and sealing compound to ensure that the concrete cures slowly and evenly. This can help reduce cracks, curling, and discolorations. The concrete slab is ready for light foot traffic around 3-4 days after placement. You can remove the concrete formwork 14 days after pouring.
- Use protective gear, like gloves and eye protection, when working with concrete. Wet concrete can irritate your skin and eyes. It is also best to use breathing protection when dealing with dry concrete mix since it is an irritant when accidentally inhaled.
- Although most prefer concrete with a smooth finish, you can give your concrete slab some texture by lightly running a broom over it.
Things to Ask Your Contractor About Concrete Slabs
If you plan to hire a contractor to do your concrete slab, hiring the best one in your area is crucial. Below are some questions you can ask your contractor to ensure that you are hiring the right one.
- How long have you been in the business?
- Do you have pictures of previous projects?
- Can you give me a line item quote?
- Can your stain or stamp my concrete slab?
- How much do you charge for sealing concrete?
Should You DIY or Hire a Professional for Your Concrete Slab Installation?
If your concrete slab is for use as pavement or walkway, you can DIY it as long as you follow the instructions above. However, if you are doing a concrete slab intended as the flooring of a structure, it might be better to leave it to the professionals, especially if it’s your first time. Hiring a professional is also recommended if you are building on a slope or uneven ground. Another instance is if you are aiming for a custom color or design.
Concrete slabs are important in construction projects; you can use them as a mobile home or prefab house foundation. You can also use concrete slabs to build a walkway for your shouse or pole barn home. Additionally, they can be used to keep your shipping container home stable. Because of their many uses, it is important that you understand how durable concrete slabs are made. Make sure you follow our Facebook page to access other helpful articles if you plan to build a DIY barndominium, shouse, shipping container home or similar non-traditional home.