The Game’s Afoot! … The Myth of Waterproof Concrete

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The Game’s Afoot! … The Myth of Waterproof Concrete

The Myth of Waterproof Concrete: a blog discussing the myths and realities of Waterproof concrete.

There are many companies that promise to make waterproof concrete. However, they are simply offering a false promise. There are two reasons why we know it is impossible to make concrete waterproof.

1) Concrete is porous and therefore water can penetrate through the pores.

2) The cement paste matrix will crack and allow water to penetrate through cracks in the product.

Unfortunately, there are many companies that tell contractors, engineers, architects and others that they can produce concrete with no porosity. They will show you pictures of epoxy-coated concrete tanks or other products with smooth surfaces. Then they will tell you that those products have no porosity. They do not understand the difference between surface finish (smoothness) and porosity (interconnected pore spaces).

The Game’s Afoot! … The Myth of Waterproof Concrete: a blog discussing the myths and realities of waterproof concrete.

I have been involved in the construction industry for over 40 years and have been writing professionally about building related issues for the last 20 years. During that time I have published hundreds of articles – mostly in trade publications. Two years ago I decided to write a book on concrete waterproofing and as part of my research I visited countless websites, read countless articles and watched countless videos. Most will be used as references to support my book, but some give me great concern because they are misleading or just plain wrong.

One of the most common topics is concrete waterproofing; or more correctly, cementitious waterproofing products that are added to the mix when making concrete. These products are designed to create a barrier within the concrete to prevent water transmission through the concrete slab and into the habitable spaces below. Actually, this is not entirely correct because these products do not completely stop water transmission; rather they reduce it to a point where it is no longer considered harmful. Nor are they totally preventative because even with these products there can be no guarantees that water will not leak through cracks or other openings in the slab (or around penetrations).

It is also important

Concrete is porous. That means that water and other liquids can penetrate the surface, causing damage from within. Learn how to protect your concrete.


I recently came across a blog discussing the myths and realities of waterproof concrete. The blog provided information on the various methods used in attempting to waterproof concrete, as well as some interesting information on the topic.

One of the myths discussed was that by using a waterproof admixture, you can achieve a waterproof concrete slab. The author cites several sources in stating that this isn’t true and that no admixture can make concrete 100 percent waterproof.

Another myth discussed was that by using an integral waterproofing admixture, you can achieve a waterproof concrete slab with only one pour. Here the author states that while the use of an integral waterproofing admixture will result in a more impervious slab than without the use of one, it still won’t be 100 percent waterproof. As such multiple pours may be needed to build up enough layers of protection to achieve true watertightness.

The article also discusses other methods for protecting concrete from moisture penetration, including topical sealers, coatings and membranes, cementitious block fillers, and crystalline technology. For each method some basic information

The myth of waterproof concrete:

You can’t make it. It doesn’t exist. Stop bothering me about it.

I am done with this one. I have been writing about the myth of waterproof concrete for over thirteen years (since I started this blog in 2005). I have written about it so many times that I don’t even know how many articles there are on the topic (I’ll have to go back and count).

I’ve explained why you can’t make it; why no one can make it; why the quest for waterproof concrete is a fool’s errand. I’ve debunked stupid claims of its existence, including those made by Concrete Construction magazine, which should damn well know better! And yet the myth persists.

The myth is so persistent that even people who should know better seem to believe that there really is such a thing as waterproof concrete. A few days ago, I received an e-mail from a guy who wanted to sell me a product that he claimed made concrete waterproof!

If you are interested, here are some links to my previous posts on the subject:

A few years ago, when I first posted this material on the web, a number of people wrote me to tell me that the idea of waterproof concrete was a myth. Well, I am here to tell you that it is not!

But in my defense, there are a number of things I was trying to get across and it seems that some people were not really paying attention. So let’s try again:

1) Waterproof concrete is a myth.

2) Waterproof concrete is possible but not common as it requires meticulous attention to detail and specialized materials.

3) The use of sealers to waterproof concrete surfaces has been around for thousands of years!

Waterproof Concrete is a myth. To all those who say it ain’t so, I say, “Then why do we have to waterproof concrete?” All concrete is porous by nature. The porosity of the concrete is not random, but directional. The porosity of the concrete is highest in the top layer and decreases as you go deeper into the slab. This means that water will take longer to penetrate into the center of the slab than it will to penetrate into the top layer of concrete. This porosity of the concrete is affected by several factors:

1. Cement water ratio: For any given amount of cement, more water means more porosity

2. Cement content: For any given amount of water, more cement means less porosity

3. Slab thickness: Porosity (and strength) increase with depth

4. Curing conditions: Porosity of the surface layer is lower for columns or walls that are cured under damp conditions than slabs that are cured under dry conditions

5. Finishing: Floating and troweling increase porosity; hand floating and steel troweling decrease it.

6. Aggregates: Harder aggregates like quartzite are less porous than softer aggregates like limestone (which may also contain

A waterproof concrete mix would be a dream come true for many building owners, architects and engineers. Indeed, one of the most common questions I get is “Is there such a thing as truly waterproof concrete?” Unfortunately, the answer is no.

There are many products on the market that claim to make concrete waterproof, but all of them are really just water repellents. They have no effect whatsoever on water pressure behind the concrete and they will not stop hydrostatic pressure from pushing water through the concrete. They simply keep the water on the surface of the concrete where it dries or runs off.

What about admixtures that actually modify the capillary structure of the cement paste so that it has less voids? This is an interesting technology and some labs report promising results. But to my knowledge there have been no actual field tests that show this type of admixture can actually stop water intrusion in a real-life application. We may see this type of admixture used more in the future, but today it remains unproven.

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