Concrete retardants increase the processing time of the concrete. A retarder should be added to the concrete if long transport routes have to be bridged.
The concrete admixture is also often used when processing bulky concrete parts. Massive components include concrete parts with a minimum dimension that is equal to or greater than 0.80 m.
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In addition, a concrete retarder optimizes working time at high outside temperatures. Temperature peaks and temperature stresses are reduced during the hardening process.
Concrete retarders slow down hydration of the concrete. In this chemical reaction, hardening of the concrete is actively prolonged by adding a concrete retarder. The areas of application for concrete retarders are diverse. We would be happy to help you select the right product.
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.’
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.
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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.
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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.
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