Coming Soon to a Theater Near You: Rising Damp and the Salt Monster!

2/22/16
Coming Soon to a Theater Near You: Rising Damp and the Salt Monster!

If the title of this blog sounds like a 1950’s B­-flick of epic science fiction proportions then let me just congratulate you on your nerdiness. If only this were a Hollywood creation but sadly, it is a very real global problem impacting conservation of historic buildings. The negative impact is certainly felt in New Orleans. Our understanding of this dastardly phenomena begins with the art of brick-making. The colony was founded in 1718 and brick-making began at the de Morand brickyard in 1725, followed in 1726 by the Batture brickyard.

Brick made locally tends to not have a lot of tensile strength which is basically the amount of stress it can undergo without failure. As rising damp and the salt monster stalk the landscape, we find that our bricks often crumble under the stress. Water is a delivery system for salt and even fresh water can contain salt. Soil moisture depends on soil type(clay can absorb a lot), groundwater, roof/surface drainage, plumbing leaks, seasonal variations, and soil evaporation. Something as seemingly innocuous as Window A/C units are actually in cahoots with rising damp and the salt monster because as they remove humidity from the air, that humidity re-condenses and that liquid drips out at the foundation of structures thus raising soil moisture. Why is this bad? As bricks suck up water, they carry salt deep within the brick and once inside, salt forms crystals that produce pressure that causes a bursting at the seams. It overcomes the tensile strength of the brick and the brick begins to fail via disintegration. If you want to continue the monster analogy, the salt eats the brick. It does not really eat the brick but the destruction is just as complete.

Throughout the years, as people restored old buildings they turned to a modern wonder known as portland cement. It was born in Britain around the middle of the 18th Century. The problem with portland cement is a twofold issue. One is that portland cement is harder than the brick it surrounds via stucco or as grout. Think of bricks as living things, as dynamic entities rather than static structures. In the summer, they expand and what they expand into should not be harder than they are or the bricks will start to crumble. So that is problem number one. Problem number two is that cement is about 4% salt in the form of gypsum. What? Exactly! Portland cement is a Trojan horse. It masquerades as a wonderful gift but in reality, it is smuggling the salt monster inside.

If the rising damp and the salt monster seem overwhelming, it is because, well they kind of are overwhelming. The fix for these buildings is not simple, quick, or cheap. You must first damp proof the structure in order to stop the flow of moisture in and that involves the expense of retrofitting via natural materials such as slate or copper that must go underneath the brick of walls and joists. This is a relatively new technique and thus there is no guarantee it will even work. After you damp proof, you must apply a poultice to the wall in order to try and pull the salt out. The poultice such as Westox Cocoon is a highly porous paper, capable of drawing the salt out. This method works best if one side of the wall is covered in the poultice while the other is continually infused with distilled water. This process can take a year or more and is subject to seasonal changes. The time alone makes this cost prohibitive for the average homeowner.

If you are starting to feel a little scared and depressed, it is because you should be scared and depressed. This is a massive problem impacting every corner of the globe, from Venice to London to New Orleans. Rising damp and the salt monster will destroy anything in their path, including museums, great architectural works of art, and the pillars supporting countless unsuspecting homes. They are out there. They are hungry. They are silently wreaking destruction. Cue horror music and close in on the face of someone screaming! What lurks along your foundation and inside your bricks?

-Sandy
Crescent City Historic Tours