What to know when you are ordering concrete:
How much do you need?
Calculating how much concrete you need can be difficult. We are here to help! Accuracy when you are figuring the dimensions of your pour is very important. If you calculate your slab at 4 inches thick but it is 6 inches in some places it could average 5 inches thick. That is a 20% difference in the amount of concrete needed. It is very important to take the time necessary to get your grade correct and even.
Here is some math to help you calculate it yourself. If you get stuck, give us a call.
For example, a patio slab that is 10 feet x 12 feet and 4 inches thick would be calculated this way:
10 x 12 = 120 square feet
120 x 0.33 feet thick = 39.6 cubic feet.
39.6 cubic feet/ 27 cubic feet per cubic yard = 1.46 yards of concrete
We recommend you order an additional 10% to cover waste and possible inconsistencies in grade. We sell concrete in quarter yard increments with a one yard minimum order. For this example, 1.75 yards would be the appropriate order.
Keep in mind that there will be an additional charge for loads less than five yards. If your placement figures between four and five yards, it may be more cost effective to get five yards and not pay the short load fee. Also, if you do not order enough and need another load the short load fees will apply just like it is a new order.
Mixes:
All concrete mixes contain four basic components. The variation of these ingredients is what makes up the different mixes for a wide variety of uses.
Link to TJCY industrial chemical
Course Aggregate – 3/8” and larger rock
Fine Aggregate – Sand
Cement – A fine powder made from limestone.
Water
Strength:
Each mix is first defined by the compression strength it is required to meet 28 days after it is batched. This can range from psi to 12,000+ psi. The most important factor in making this strength is the water/cement ratio.This ratio needs to be maintained from the time it is batched into the truck all the way until initial cure is complete. (see Slump and Curing below)
Course Aggregate Size (maximum) –
Our mixes can be ordered with 3/8”, ¾”, or 1 ½” course aggregate. Each of these has its own particular use as well as its own challenges. Keep in mind, Duke City uses a combination of these to make our mixes perform above standards while still being affordable. The size of the aggregate mentioned in the mix is the largest size in the mix and cannot exceed 33% of your smallest dimension.
3/8” Course aggregate is easier to pump, better to fill in smaller spaces, but requires more control joints, extra cement to make the same strength and, therefore, more expensive.
¾” Course aggregate is the most commonly used because it is very workable and has great strength.
1 ½” course aggregate is best used in thicker placements (8” thick and over), but is difficult to finish.
Slump:
The slump of concrete is a way to measure the workability of the concrete. It is most commonly associated with the amount of water in the mix. The test is completed by placing the concrete in a 12” tall hallow cone and then lifting the cone up slowly. The concrete will fall or “slump” down as the cone is pulled up. The number of inches the concrete falls is the slump. If the concrete has a high content of water the slump will increase. Most mixes are designed for a 4” slump. If your project requires more workability additional water reducers can be added to increase slump and maintain strength.
Admixtures:
There are a wide variety of concrete admixtures available to help you complete your project in the best and most cost effective way.
Air Entrainment – all concrete exposed to the outside elements needs to have air entrainment. This admixture creates small bubbles inside your concrete to allow moisture in the concrete a place to expand when it freezes. Without this outlet the concrete will fail the first time it freezes. The down side of using air entrainment is the finish. You CANNOT use a steel trowel finish on air entrained concrete because it will peel the surface of the concrete and ruin your project.
Water reducers – All mixes Duke City offers have water reducer in them to help with strength and workability. We are able to use water reducers (aka – Midrange) to increase slump and workability.
Accelerators – In colder weather or if a faster set time is required accelerators can be added to help the concrete set quicker.
Retarders – If you want to slow down the set time or your job site is more than an hour drive time from one of our plants we recommend using retarder.
Fiber – fiber reinforcement is a great way to increase early strength and reduce surface shrinkage cracking by adding small strands of fiber to the mix to help it bond together.
On the Job Site
Job site safety and access are the responsibility of the contractor or owner of the property. Here are a few questions to ask yourself before ordering a load of concrete:
Will the truck fit onto the job site? A mixer truck is 8 feet wide and 12 feet tall and will need additional room on all sides to safely maneuver around the job site.
Do you have a way to get the concrete from the truck to the final location? Every truck can reach about 15 feet directly behind the truck with chutes, but can only flow down from gravity. If the truck cannot access it, do you have access to a concrete pump or wheel barrows and enough help to get the concrete to the placement? Keep in mind you are allotted 10 minutes per yard to unload the truck or you could be charged truck time.
Does the truck have a place to washout when the pour is complete? Our trucks need to remove all wet concrete from the chutes before leaving the job site. This can often be accomplished with a wheel barrow to catch the water and the waste.
As a concrete flooring installer, you know that moisture control is crucial for ensuring a durable, long-lasting floor. But did you know that moisture deep within the slab can still rise to the surface and wreak havoc on floor coverings?
That’s why vapor retarders are a standard in the industry. These essential barriers prevent ground moisture from migrating into the concrete slab, where it can damage adhesives, cause swelling, and lead to costly flooring failures. In fact, failing to install a vapor retarder can void flooring warranties and leave you responsible for expensive repairs.
So, what do you need to know about choosing, installing, and maintaining vapor retarders?
In this guide, we’ll cover:
✅ What a vapor retarder is and why it’s critical for flooring success
✅ How vapor permeability affects moisture movement
✅ Best practices for installing vapor retarders under concrete slabs
✅ Industry standards and guidelines for proper moisture control
By understanding and following best moisture control practices, you can prevent flooring failures, protect your reputation, and ensure high-quality installations. Let’s dive in!
A concrete vapor retarder is any material that prevents moisture from entering a concrete slab. Vapor retarders are used because while fresh concrete is poured wet, it’s not supposed to stay that way. It needs to dry and then stay dry to avoid flooring problems.
If you’ve ever had a problem with a basement floor (or any concrete floor), you know the kind of damage that too much moisture can cause. Moisture enters concrete in various ways, including via the ground, from humidity in the air, and through leaky plumbing that passes through a slab.
Of course, the moisture was also in the original concrete mixture.
There are only one-way moisture leaves concrete, though, and that’s via its surface. If you have a concrete floor in continuous contact with a source of moisture, you will have problems.
This is why a vapor retarder under concrete is essential. Vapor retarders are a way to keep moisture from getting into the concrete.
Note: A vapor retarder is not the same as an underlayment. However, some underlayments act as vapor retarder.
Vapor retarders have varying degrees of permeability, expressed in perms. The higher the number, the more permeable the material.
You’ll hear people interchangeably using the terms ‘vapor barrier’ and ‘vapor retarder.’ In this article, we will use the term ‘vapor retarder.’
Want more information on retarder in concrete? Feel free to contact us.
The acceptable degree of vapor retarder permeability depends on the application. While a water vapor permeance of less than 0.3 perms is recommended, a higher permeance rate is usually considered acceptable for residential use.
However, the vapor retarder under the slab must have a lower degree of permeance than the flooring (or floor covering) above the slab. A moisture imbalance could eventually cause a flooring failure if it doesn’t.
ASTM International gives specific guidelines in ASTM E-17 and ASTM E for the use, installation, and inspection of vapor retarders used under concrete slabs.
One word: adhesives. Too much moisture in concrete is a problem because it can cause pH changes that destroy adhesives. Here’s what happens.
Excessive moisture in the concrete allows soluble alkalies in the concrete to move to the flooring adhesives causing the adhesives to break down. After this happens, the adhesive can no longer hold down the floor covering. This can result in flooring failures such as swelling, bulging, or other problems.
Shop Rapid RH L6
In a word, yes. Here’s why.
There’s almost always water underneath a building site. It may not be near the surface, but that doesn’t mean it’s not there. This water can move up through the soil and come into contact with the bottom of a concrete floor via capillary action.
Capillary action can be stopped by installing a capillary break, a layer of crushed rock between the subgrade and the slab.
Capillary breaks do a good job of stopping water in its liquid state from reaching a slab. However, they can’t stop water in vapor form from reaching and entering a concrete slab. Therefore, there needs to be something underneath the slab that prevents vapor moisture from entering.
You might also need a vapor retarder for liability reasons because most manufacturers of flooring include vapor retarders in their installation guidelines.
According to the Guide to Concrete Floor and Slab Construction published by the American Concrete Institute, a vapor retarder should not be less than 10 mils thick. (A mil is one-thousandth of an inch.) You might need an even thicker barrier if you cover the material with sharp angles.
Bottom line: Vapor retarders need to be strong enough so they don’t easily puncture. If they do, moisture will get in, and that’s what you’re trying to keep out.
Most vapor retarders are created using polyethylene or polyolefin sheets that are strong enough (at least 10 mils thick) to tolerate the kind of heavy construction activity that goes on over concrete subfloors.
What type of moisture retarder should be used and where it should be installed is debatable. Some think vapor retarders can cause slabs to curl and that simply pouring concrete directly onto a granular base (gravel, crushed rock, etc.) should be enough.
Others see vapor retarders as essential and argue that they prevent adhesive failures, retard the growth of mold and mildew, and even prevent certain noxious gasses from entering a building.
However, the current practice recommended by the American Concrete Institute is to apply a heavy-grade, non-penetrable vapor retarder with the lowest possible permeance for the application over a layer of granular fill (crushed rock, gravel, etc.). The concrete slab is then poured on top of it.
Note: An earlier practice for vapor retarder involved placing a “blotter” layer between the vapor retarder and the concrete slab. This eventually fell out of use because keeping the ‘’blotter’’ layer dry was hard.
Generally, you’ll want to use a low-permeance vapor barrier when protecting a slab that moisture-sensitive materials like adhesives and floor coverings will cover.
Shop Rapid RH L6
If you want to learn more, please visit our website acrylic acid.