Is Concrete Waterproof

Is Concrete Waterproof?

In Technical Details by Giovanni ValleLeave a Comment

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If you ever had to deal with musty smells in the basement or have footpaths broken into pieces, then you should know that it might be caused by water getting into the concrete. You may have asked yourself: isn’t concrete naturally waterproof?

Concrete is not waterproof. Despite not immediately seeing water leak through a slab of concrete, water does get through the spaces in between its particles. And water can break the concrete down eventually, causing it to chip off or leak through and allowing more water to cause more damage.

Read on to find out more about why concrete is not waterproof, and what are great ways waterproof it.

Why Concrete Is Not Waterproof

By very definition, waterproof means that water cannot get into the material, even if it spends a long time immersed in water. 

Concrete, on the other hand, is made up of cement, sand, and gravel. You add in water and mix these aggregates. When the water evaporates or dries, it will leave spaces filled with air in between the aggregates.

The network of holes and channels looks like your body’s capillary system, and as such, it makes the cement porous. According to Komsol, around 20 percent of hardened concrete is made of air from where water used to be.

Additionally, the more water that goes into the mixture of gravel, sand, and cement, the more porous the concrete is going to be. It is also made weaker.

Because of the composition of concrete and the eventual spaces between the particles, this material is not waterproof. Water can seep into porous concrete and degrade it over time.

The National Precast Concrete Association explains that two things can affect the water tightness of concrete.


Porosity refers to how many voids or openings exist on a certain material. As you already know, concrete is naturally porous.

To make concrete more waterproof, you can control the distribution and size of the pores in it to limit how much and how far water can get through.

There are two types of pores:

  • Gel Pores – are small holes in concrete that are a part of the glue that holds together the gravel, sand, and everything else that you mix to make concrete. Because they are tiny, they do not present a problem as far as water protection is concerned.
  • Capillary Pores – are more of a problem. These larger pores are formed when there is too much water in your cement mix. What’s more, capillary pores may be interconnected, which makes your concrete permeable.

Porosity is expressed by volume per volume, such as cubic inches per cubic inches or cubic millimeter per cubic millimeter.


Another concept that you should know about waterproofing and concrete is permeability, or how easy it is for liquids such as water to get into or flow through the porous material. 

To make it easier to understand, when you say water can get through concrete at an inch per second, then you are talking about permeability. Even the best concrete is permeable, but it becomes more permeable when the water to cement ratio is high, as well as when the concrete time is inadequate.

High-quality concrete has low permeability, which means that it takes a while for the water to travel through the pores.

Other Weak Points 

Concrete can also develop weak points over time. For example, if you bore holes into a concrete wall, that hole will be another way for water and moisture to permeate into the concrete. Joints between two concrete components are also weak points.

Why Should You Waterproof Concrete?

According to this site, waterproofing is a must for concrete that is in below-grade areas so that water cannot get through and cause damage to the structure. If you are building in a low-lying area or an area that is prone to flooding, it’s not even an option but a necessity. 

Water can get into concrete as water pressure increases capillary action, or as water vapor gets into the pores. It can also enter via cracks, defects in the concrete, or improperly installed or designed joints. Sometimes, your enemy is not even water, but chemicals used at the building site.

Some chemicals can attack concrete and break it down as well. Even the most common and organic acids, such as fruit juices, sour milk, some salts, and untreated water can cause concrete to deteriorate. Animal wastes are known to oxidize and damage concrete, too.

Waterproofing can guard against these chemicals and materials from even getting into concrete. Plus, it can protect any reinforcing steel embedded inside.

How Can You Make Concrete More Waterproof?

The best way to make concrete waterproof is to observe good mixing practices, such as using the right water to cement ratio, using top-quality aggregates, or creating and using high-strength concrete.

Use High-Strength Concrete

According to this site, regular concrete is what you have when you mix the cement according to what’s written in the instructions on the packet. Meanwhile, high-strength concrete is more durable when compressive strength is the basis.

TypeRegular ConcreteHigh-Strength Concrete
Compressive strength20 to 40 megapascal (2,900 to 5,800 pound-force per square inch)40 to 140 megapascal (5800 to 20,305.3 pound-force per square inch)
WorkabilityGood texture and stickinessSticky and may be more difficult to handle or place
Permeability1 centimeter / 10 -10  second.1 x 10 -11 to 1 x 10-13 cm/sec

High-strength cement also has lower water to cement ratio and adequate curing period, which helps make it less porous, at around 8.3 to 9.1 percent. Concrete made with water to cement ratios of 0.4 and above and cured for one to seven days will have porosity levels of 11.3 to 13 percent.

In short, high-strength concrete is the easiest way to make sure that your concrete is watertight. 

Densifiers can fill in the pores in the concrete to prevent water from getting in. These products usually have silica fume in them. They react with water quickly and can even make your concrete stronger. As such, densifiers are often used when producing high-strength concrete.

Buy something like the Foundation Armor S2000 Concrete and Masonry Sealer, which has professional-grade and pure sodium silicate.

Use the Right Amount of Water

Using too much water can make your concrete more porous and weaker. However, using too little water will make the concrete look and feel like moist sand. As such, it will not be compacted, and it will be near impossible to cast.

Researcher Ralejs Tepfers recommends a water to cement ratio of 0.3 to 0.4. At this rate, all the water you use to mix the components is going to be used up to wet the cement. 

For instance, if you are mixing a kilogram (2.2 pounds) of cement, then you should use 0.3 to 0.4 liters (10.1 to 13.5 ounces) of water.

Take Note of the Minimum Cement Content

If you have a rich concrete mix, you can get a more watertight concrete, according to the National Precast Concrete Association. They recommend that you have a minimum cement content of 564 pounds per cubic yard (255.8 kilograms per 0.8 cubic meters). 

You could also use finer cement, which lends itself to more workability and less bleeding. Or you can use supplementary materials that can help make the concrete denser with very low permeability and porosity. 

Some materials you can use includes:

  • Slag
  • Silica fume
  • Fly ash

Use Better Quality Aggregates in Your Mix

Aggregates make up around 60 to 75 percent of your concrete’s volume. Fine aggregates are usually crushed stone or sand that are less than 0.2 inches (five millimeters). Coarse aggregates are those that measure more than that, with average sizes at anywhere between 0.38 to 1.5 inches (9.5 to 37.5 millimeters)

What you’re looking for are round and smooth aggregates that require less water to become workable. The shape and texture of your aggregates can either make your concrete more or less dense.  

Further, the NCRPA recommends rounded and coarse aggregates because these materials can be placed more uniformly. Fine sand is also recommended.

Integral Waterproofing

As a general rule, you need to waterproof concrete that gets standing water, such as on flat roofs or ice damming. For walls, sidings, foundations, and everything else, you can get away with water-resistant products.

Waterproofing can be done from the start when you’re mixing the cement, gravel, sand, and water. But aside from the best cement mixing practices, there are substances that you can add to make the concrete more waterproof.

These processes are called integral waterproofing. It’s better than applying a hydrophobic or water-repelling membrane or coating because the waterproofing is internal and, therefore, cannot be damaged or torn, and will not wear out over time.

What’s more, if your concrete does crack, integral waterproofing makes it easier to repair any damage. As such, integral waterproofing gives concrete long-lasting and comprehensive protection. 

Moreover, integral waterproofing solutions are very cost-effective and can save you a lot of time. While there are dozens of admixtures that you can buy, these products generally fall under three categories:

  • Crystalline formulations
  • Densifiers
  • Water repellents

Use Plasticizing Additives

Aside from meticulously measuring how much water you add, you can also use plasticizing additives. A product like the Fritz-Pak Concrete Superplasticizer Additive allows you to use less water without making the concrete mix too sandy in consistency. 

You can use at least 20 percent less water and still have an easily workable mixture. What’s more, it reduces shrinkage, creep, and cracks while filling in the spaces in between the particles, so water doesn’t easily get in. 

Using plasticizing additives also helps you save on cement, as you will be needing around 15 to 20 percent less cement.

If you use a plasticizer, the resulting concrete is much more durable and can resist breaking or cracking under compression. However, plasticizers are not magic, and they work well only when you have a good mixture.

Pros of Using Plasticizing Additives

Plasticizers can make concrete mixes more workable without you needing to add more water, thereby allowing you to achieve the optimal water to cement ratio. And because you are using less water that will eventually evaporate from the mix, it reduces the permeability of the concrete.

With less water to contend with in the first place, cement dries faster. Plasticizing additives also reduce the amount of cement used. 

Mix in Powdered Crystalline Admixtures

Another set of products that you can use to make concrete more waterproof are crystalline admixtures. These are powdered and dry, and they use the available water and moisture to create crystals inside the concrete.

When the crystals are created, the pathways and spaces between the particles are closed off. As such, water cannot get inside the concrete, and the whole thing becomes a barrier.

Researchers from the Czech Technical University in Prague reiterate the waterproofing properties of crystalline admixtures and note that this effect can already be seen on the 12th day after you create the concrete.

Pros of Using Powdered Crystalline Admixtures

The use of crystalline admixtures results in more durable concrete, and waterproofing is observed as early as the 12th day. It also increases the compressive strength of the concrete, or its ability to handle compression without breaking.

However, it does prevent the evaporation of water vapor from concrete by anywhere from 16 to 20 percent and may result in the concrete taking a longer time than usual to fully harden.

Cover the Surface With Water-Repelling Material

If you already have an existing concrete structure and you need to waterproof it, you can use sealants and membranes to keep the water out.

Use Modified Bitumen Products

Modified bitumen products like the FixtureDisplays Black Bitumen Paint are used to fix cracks on your driveway or to stop leaking roofs. It leaves a layer of a rubbery material that helps keep water out.

Asphalt by itself is temperature-sensitive and not as elastic as you want it to be, which is why polymer materials are added to it. The resulting compound has more tensile strength, is self-healing, and can withstand acidic soil, but without the harmful substances that are traditionally used to bind asphalt.

Put Waterproof Sealants to Seal the Surface

Admixtures or substances that you add to your concrete mix are excellent choices because they make the concrete waterproof even when the upper layers are flaked off or have eroded. Every part of the concrete can ward off water.

However, one of the biggest disadvantages of admixtures is that they don’t seal the surface of the concrete. Because of that, the bacteria, algae, lichen, moss, and other growths can attack the surface, which may lead to cracks and porosity over time.

What does this mean? Even when you use admixtures, you might want to consider using sealants to guarantee the highest level of waterproofing for concrete.  

You will need sealants if you have an existing concrete surface that uses the traditional mix of gravel, cement, and sand. To waterproof such surfaces, you will need sealants.

Products like Essential Values Concrete Sealer can protect concrete surfaces by keeping moisture out, helping it look new without cracks, pitting, or spalling.

What’s more, this product can help protect concrete from ions, salts, stains, fungus, molds, freezing, and mildew.

A Word About Volatile Organic Compounds

Volatile organic compounds are those that quickly become gases or vapors. They are released from burning wood, gasoline, natural gas, or other fuels, or as fumes from consumer products such as thinners, paints, some waterproofing products for concrete, and moth repellents, among others.

However, you should be aware that even short-term exposure to VOCs can be bad for your health. Some health effects include:

  • Dizziness
  • Visual disorders
  • Memory problems
  • Respiratory tract irritation
  • Eye irritation
  • Headaches

Longer periods of exposure can lead to:

  • Irritation of the throat, eyes, and nose
  • Fatigue
  • Cancer
  • Dizziness
  • Nausea
  • Liver or kidney damage
  • Damage to your central nervous system 

Because of this, it’s not recommended to use products with VOCs. If you do, make sure that you work in an area that is properly ventilated and meticulously follow the manufacturer’s advice.

Plus, you should store these products in a shed or garage. 

Final Say: Waterproofing Concrete Is Doable

Concrete is far from being waterproof because of its porous nature. The spaces in between the particles in concrete make it permeable to water. 

The thing is, there are times when waterproofing concrete is a must, especially in areas where it is left with standing water. What’s more, keeping water out of concrete helps make it become more durable and longer-lasting.

Concrete may not be naturally waterproof, but there are a few ways to make it more hydrophobic. Your main goal is to reduce the amount of water used in the mix, and apart from meticulously following mixing instructions, there are products and best practices that can help you with that. 


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