I first learned about penetrating water-repellents for masonry, a PROSOCO specialty, when I arrived here at PROSOCO 13 years ago in July.
These remarkable treatments seemed completely magical to me then, and still do. It’s amazing to me how these substances — many of them water-based themselves — can bar entry of liquid water into the substrate, while permitting water vapor to evaporate out.
Newbie though I was then, I could still see the advantages. Water can’t get in, to freeze and expand, and crack and spall the masonry — or to make a moist environment for mold. Moisture already in isn’t trapped within the microscopic pores and capillaries of the brick, stone or concrete — it can evaporate out.
That characteristic is often referred to as “breathability.”
My first thought was — if moisture can get out, but not in, wouldn’t the masonry eventually get so dry that it would crumble into dust? However, this dire circumstance has never come to pass. Evidently, the laws of physics don’t work that way.
The opposite problem — too much water getting into unprotected masonry does create dire circumstances.
One of those problems is biological growth. If you think the preceding photo looks bad, you should’ve seen it in person. Eventually they cleaned the building, using PROSOCO products, natch. The cleaning contractor recommended a penetrating water repellent for the cleaned courthouse, but I don’t know if that ever got done.
If it didn’t the biological staining will be back.
Allen Fieldhouse got treated with a masonry-strengthening water repellent Weather Seal H-40, and the black gunk hasn’t returned.
North elevations are particularly susceptible because they seldom see direct sunlight. So once wet, they often stay wet, which is just how mold likes it.
Put a penetrating water repellent on that masonry, and the water can’t soak in to provide a moist environment for mold.
Here’s an example. Water beads up, unable to penetrate this limestone where I treated it with a water-repellent. Mold won’t find that a good place to thrive, because of lack of moisture. The water soaked right into the untreated edge, making it more susceptible to biological growth.
In the photo below, water penetration has popped off the faces of the bark-faced brick in this retaining wall. The damage could have been caused by freeze-thaw cycling, or by the build-up of salts within the masonry fabric (subflorescence). Water penetration causes both problems, so either way, keeping water out of the masonry prevents the damage, as well as the mold growth.
Penetrating water repellents work by soaking in and lining the pores of masonry substrates with water-repellent molecules. Visualize a molecule with an umbrella on top and hooks on the bottom. The hooks chemically bond the water-repellent to the substrate. The net effect of all those little molecular umbrellas is to create a surface tension that keeps liquid out of the pores.
There’s not a thing in the world, however, to stop vapor from evaporating out, if it needs to.
Because the treatment does its job from beneath the surface, there’s seldom, if any, change to the look and feel of the masonry. That’s particularly important to restoration professionals.
They’re right to be concerned. Film-forming water-repellents, which try to protect the masonry by forming an impermeable layer over the masonry, can seriously degrade a building’s appearance.
Because they’re not “breathable,” these treatments trap moisture within the substrate until it breaks out. The results are ugly. Where the coating fails, more water gets in. Where the coating stays intact, it traps the additional moisture, so the problem gets worse and worse faster and faster.
The only solution is to remove the failed coating, and replace it with a penetrating water-repellent.
That’s what happened at the historic Folly Theater in downtown Kansas City. You can read the full story here.
Water penteration into masonry and concrete causes plenty of other problems besides mold growth and surface damage. Lime run and efflorescence are two other common problems. As a matter of fact, uncontrolled water causes more damage to buildings than anything else.
Though they’re major components, water-repellents are still only one part of the system for stopping water damage. Expertise, structural integrity and a reliable, tested water repellent all work together. Still looks like magic to me, though.
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