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How to Waterproof Concrete

Concrete is wonderful material and has been used in some form for millennia. Concrete is extremely durable, moldable, and relatively easy to use. Concrete in its raw form, however, does have a few weaknesses, which include vulnerability to water.

industrial worker on construction site laying sealant for waterproofing cement

Most concrete repairs are in response to cracks or flaking caused by ice forming in or on the surface. Waterproofing prevents this by sealing the surface of the concrete against water and ice. In most cases, this project will involve a sealer, top coating, or paint.

Today we will discuss the most common form of concrete waterproofing, which is applying a concrete sealer. 

What Is Concrete?

Concrete is a mixture of a few ingredients that, when combined, harden to form a very hard, dense material. Concrete is available in many mixtures depending on what it will be used for and where it will be installed. A basic mixture of water, cement, fillers (aggregates), and air. These ingredients can be used in various ratios, depending on the purpose of the concrete. Over time, manufacturers of concrete have fine-tuned the process and incorporated additional materials for specific purposes.

For example, calcium chloride is a common compound added to concrete to help control how fast the concrete dries and under what conditions. These and other additives can make concrete stronger, adjust curing time, and help the concrete harden in cold weather. Fiberglass strands, recycled plastics, and other by-products can also be added to the mixture to improve its resistance to temperature changes and workability. 

What Is Concrete Waterproofing?

Waterproofing concrete is the process of sealing pores in cured concrete that may absorb moisture. In the case of a concrete pad, this waterproofing seeps into the hardened surface of the concrete and closes all of the tiny pores that can freeze and damage the surface.

Concrete waterproofing products are often very thin (about the consistency of water) to allow the product to be absorbed into the smallest of pores. Concrete waterproofer is usually applied in several thin coats, as opposed to one thick one. The product is often applied in certain conditions, like a warm, sunny day to allow the product to cure rapidly. 

Why Does Concrete Need to Be Waterproofed?

Concrete may look very solid and dense, however, air gets trapped in the mixture and can allow the concrete to act as a sponge. Some concrete mixtures are less dense than others, but even completely cured concrete will be susceptible to water damage to some extent.

As such, outdoor concrete is vulnerable to damage from ice and snow because as water freezes into ice, it expands in size. If a concrete pad is waterlogged and then freezes, the expansion of the ice will actually be strong enough to break the concrete. 

For decades, concrete installers have battled this problem with various means. One of the earliest was to paint the surface of the concrete so that water could not be easily absorbed.

This method helped, but high-quality petroleum-based paint was usually required to withstand the constant wear concrete often experienced. This also required periodic maintenance to keep the surface completely covered.

As time went on, other treatments were introduced, such as latex-based (water-soluble) paints and transparent sealers. In recent years, concrete manufacturers have introduced other ingredients such as calcium chloride, which works like salt to help prevent ice from forming.

In modern construction, paint is still used occasionally, but it will often be replaced by products specifically designed for concrete, such as concrete waterproofers.

What Are the Advantages Of Waterproofing Concrete?

Waterproofing concrete seals and protects the surface of the concrete to prevent water from being absorbed and freezing. Waterproofing extends the quality and useful life of the concrete by:

  • Adding additional material to the surface, insulating the concrete from wear
  • Making the surface very smooth and easier to clean
  • Keeping the appearance like new
  • Allowing rainwater to bead, making it easier for the concrete to shed water

However, it should be noted that waterproofing concrete does require periodic maintenance, usually every couple of years. Some products claim to last longer than others, but generally speaking, the surface should be inspected yearly for wear.

How Do I Start Waterproofing Concrete?

Waterproofing concrete is quite simple and can easily be accomplished by a do-it-yourself homeowner. All concrete waterproofing products will have specific directions for applying the product, but the method will be similar to others. Here are a few tips to get started applying waterproofing to concrete:

Step 1. Prepare the Concrete

The first step is probably the most important to the success of the project, which is to make sure the concrete is prepared to accept the waterproofing. In most situations, this will just be done to ensure that the surface to be waterproofed is clean and dry.

The surface should be as clean as possible because the waterproofing is also a sealer. This means that any debris on the surface will be sealed in. Insects, dirt, and debris will essentially be adhered to the surface and must be manually removed after the waterproofer has cured.

Cleaning is also important because stains or other blemishes on the surface may prevent the sealer from contacting the concrete. If the waterproofer cannot contact the concrete, it will usually flake off over time.

Therefore, the surface should be broom clean at a minimum, but it can also be pressure washed to achieve the cleanest possible surface. This technique is common when sealing old concrete that may have years of buildup. In short, the cleaner the concrete is, the better job the waterproofing will do.

Step 2. Make Sure the Concrete Is Dry 

As mentioned earlier, the concrete to be waterproofed must be as dry as possible. One of the benefits of waterproofing concrete is that the material is actually absorbed by the concrete, as opposed to just sitting on the surface. Obviously, the dryer the concrete, the more waterproofing it can soak up.

For this reason, most concrete waterproofing is done in the summer months. However, in some geographical areas, winter is actually drier than summer, so it is best to choose a waterproofing product designed for the area. 

Step 3. Applying the Waterproofer 

Although the process will vary slightly from manufacturer to manufacturer, the waterproofing can be sprayed, brushed, or rolled onto the surface. Some products also contain additives that will affect the sheen, texture, and color of the material.

For example, in areas that receive harsh winters, some users will incorporate sand or other rough material to improve the friction on the surface, reducing slippery ice formation. Others may include a tint that aesthetically improves the look. Regardless, the most important aspect of any waterproofing project will be complete coverage. Even a small area left unsealed can allow the concrete to absorb water and cause cracking. 

To begin applying the waterproofing, most professionals will simply pour the material onto the surface and spread it according to the directions. With most products, multiple thin coats will be superior in performance to one or two thick ones. Professionals will use a push broom, paintbrush, or paint roller to apply the material as directed, to the recommended thickness.

The waterproofer is then allowed to dry to the touch and the process is repeated. It is difficult to apply too much waterproofer, so generally, more is better. However, most do-it-yourselfers seek a balance between thorough coverage and cost.

Step 4. Test the Seal

The final step will usually be testing the function of the waterproofer. Each product will recommend the conditions needed for curing the product, but most will allow testing of the surface in a few days.

Some versions may require more or less time, depending on the ambient temperature and humidity. In any case, the testing procedure is the same, which is simply to see if the surface will bead water.

This is usually done by simply pouring water on the surface, in both large and small amounts. If the product is effective, water will bead and evaporate without ever contacting the concrete. If the surface appears to bead water in some places more than others, the waterproofing is too thin and should be re-applied.

Most products will need to be reapplied after a couple of years, but this may vary depending on the wear the surface is subjected to. With most products, a sheen from totally flat to semi-gloss is available, so consideration should also be given to the use of the concrete.

As mentioned previously, if the surface is already slippery, waterproofing will likely increase this effect, so sand or other rough material can be added to roughen the texture, providing more traction.

Does Waterproofing Damage Concrete?

No. Because the waterproofer bonds with the concrete, it actually strengthens it. This effect is minimal unless the waterproofer is exceptionally thick, but the waterproofer does form a type of shell. Depending on the geographical location, some concrete installers will augment this waterproofing by laying builders’ plastic under the concrete. This prevents or reduces groundwater from seeping up through the concrete from below, plus it usually reduces the amount of concrete needed.  

Waterproofing Concrete Makes a Durable Surface More Durable

Waterproofing is an inexpensive way to add years of useful life to concrete. Much in the same way paint adds life to a home, waterproofing concrete will make the product last much longer, stay in better condition, and look better. Waterproofing is well within the skills of a typical homeowner and requires little in the way of training and tools. The most important part of the process is to select the right product, apply it according to the directions, and be patient.

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