Sheer magic

This totally permeable cheesecloth, treated with masonry water-repellent Weather Seal Siloxane PD, illustrates what protective treatments are all about. Liquid water cannot go through the treated cloth, porous as it is, and beads up on the surface. Water vapor can go through, however, as the rising steam shows.

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.

The black gunk is mold on the (then) 100-year-old limestone of the North elevation of the Douglas County Courthouse here in Lawrence.

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.

North elevation, Douglas County Courthouse after cleaning, with PROSOCO products, natch. But without a water-repellent, the biological staining will come right back.

If it didn’t the biological staining will be back.

Here’s another North elevation shot. This is historic Allen Fieldhouse at the University of Kansas, getting cleaned for its 50th b-day in 2005.

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.

I poured water on this limestone sample after treating three-quarters of it with Natural Stone Treatment, a water-repellent specially made for limestone.

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.

Water penetration has popped the faces off this bark-faced brick. There’s also plenty of dirt and mold.

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.

This graphic shows how penetrating water repellents line the pores of masonry substrates with hydrophobic molecules.

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.

Here’s a close-up of a failed film-forming protective treatment. The force of the moisture evaporating out caused the coating to debond.

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.

A failed film-forming coating is removed from the orange brick at the historic Folly Theater in Kansas City. Guess which side has yet to be cleaned.

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.

One of my favorite photos. I treated this brand-new masonry With Weather Seal Siloxane PD, then hit it with the garden hose, then got the photo on a sunny summer day. Love this job!

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