Feedback: Waterproofing Agents On Concrete

We posted a blog by Senior Editor Eric Herman on Jan. 25 that dealt with the use of waterproofing agents on concrete ("The Waterproofing Conundrum"). Several readers weighed in on the article, including the two below.

To say concrete at a compressive strength of 4,000 psi makes you feel comfortable in regards to structure or waterproofing ability is wrong. Compressively speaking you can have a strong concrete mix design "6,000 to 7,000 psi" but the actual factors of whether the material is watertight is based on its density more than anything. Yes higher-compressive-strength materials typically demonstrate higher resistance to permeation, but the issue of diffusion "permeation through pores and molecular gaps" is solved on the molecular level.

I see the permeability of concrete as a larger problem than we like to admit. The negative side effects are seen in colder climates such as the Northeast more often than in Southern California. Trapped water freezes, expands and damages the structure and anything attached, plain and simple.

By absorbing water you are in fact absorbing carbon dioxide and acidic compounds which results in lowering the pH levels around the steel reinforcement resulting in corrosive cells to form "rust." Iron oxides developing on steel placed too close to the surface of the concrete equates to spalling.

Also, you can have plaster delaminating as the surface's "chemistry" changes beneath the finish. We all know these are not the most common issues we face as builders but we do know deep down they are issues, just not life and death.

If money was no issue you could use a crystalline-based admixture every time, I'm just not sure it's economical. High water tables always remind us we are building a structure underground that will potentially be exposed to water constantly. In these cases, maybe the integrity of the builder should kick in and explain to the customer why an admixture is needed.

My final point is this: Even if you could make the statement at "x psi" shotcrete/gunite is 99.9% moisture resistant, as Bill stated in the article, human effort in applying the material still is a factor. Let's be honest, after 30 yards of shooting and 10 more to go, your nozzle man is not going to be following the textbook.

Remy Genot, Dreamscapes Pools, Toledo, Ohio

It is simple. Let us not rely on the assumptions of what could or might happen during the pool building process. Let us instead rely on the experience of experts (like Skip Phillips), who have been hired to do forensic testing of failed projects (hundreds of them in fact) and have determined that rarely is a concrete shell installed 100 percent correctly, and rarely is it 100 percent waterproof. It is that issue that is also often the cause of simple or catastrophic failures of these projects.

Let us then look to that data and the difficulty of the projects we construct, and recognize that the only proper way to construct a pool vessel intended to hold water (or salt water) and protect that structure is to waterproof it. Period! The data tells us that it is a necessity, the chemistry tells us it is a necessity; don't wait till a lawyer tells you it was necessary.

Rick Chafey, Red Rock Contactors, Phoenix, Ariz.

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