Preservation 101: Water is a B****

Like that ex who has your Facebook password, water is a vicious and insidious thing that can destroy a building before anyone notices a leak.

This was the view inside one an abandoned building in SE DC last week- between an internal leak and the heavenly deluge that hit DC, this former kitchen had its own private waterfall.


There’s no recovering from that mess.

So how does water get in, and what does it do?

This is the first of a series talking about the ways water can get into a building, why humans persist in inviting water into our buildings, and what kind of damage it can do. We will also explore why it’s perfectly fine for water to get in as long as it goes right back out. 

How water gets in #1

It used to be that water could get into a building one of two ways: up or down.

Water could either come in through a leaky roof (duh), or wick up from the ground. Wicking means that water can be induced to go against gravity by means of capillary action. Water’s natural cohesive properties plus surface tension cause porous materials such as bricks to absorb a specific amount of water by drawing it through microscopic channels in the brick. In buildings, this is known as rising damp.


Water tables and gutters keep water away from the foundation so that there is less opportunity for wicking. If a building’s sitting in a puddle, you canna change the laws of physics.

Damp courses work to alleviate the effects of wicking through evaporation, because in wet places like Northern Europe they figured out pretty quickly that you can’t keep all the water away from the building. These are generally a few courses above ground level so that water pushed away from the building will evaporate most quickly.

Sometimes, damp courses are made of an extremely dense, hard brick that doesn’t absorb water as well. Less-intelligent individuals also sometimes use a physical plastic or metal barrier in between courses to prevent wicking. This is dumb- if the water doesn’t have anywhere to go, it will just destroy the brick below the barrier and water always wins. Like your ex, you can’t argue with crazy and you can’t fight with water.

The other way a damp course can work is to actually be porous, with vents to let moisture evaporate out before it works its way upward. This, from Ernie at Masonry Solutions is a weep joint, an actual gap in the mortar done on purpose by the original mason.


This house uses a decorative cast-iron foundation vent to help it breathe- necessary in flood-prone places like N’wahlins.


Of course, lime mortar itself is porous and works very very well to ventilate itself under normal non-flood conditions. Remember that temper concept? The constant shifting of material and the rigidity of temper means that lime mortar moves water pretty well, faster than brick. The faster water moves through the wall, the faster it’s going to hit air and evaporate. Sometime this can be a problem in places where the groundwater contains a lot of salts- this is called efflorescence and is a discussion for another day- but generally it’s a good thing because it keeps water away from brick. This is particularly important in places where temperatures can drop below freezing. If water is moving through a brick when it freezes, the laws of physics kick in again and pop goes the weasel.


Salt deposits or efflorescence on a brick wall where water has evaporated out, but left non-evaporable (yes, I made that up) salt behind. Not a bad thing unless the salts are corrosive to your brick.

Ventilation is also another reason why you NEVER EVER mix your mortars. Hard modern mortars don’t vent well, which is why weep joints and weep tubes are very common in modern buildings. In historic buildings, the lime mortar helps with moving water out of the building and away from the bricks. Cover these breathable, sacrificial mortar joints with hard cement and suddenly, all the water goes into the bricks.


As you can see, the Portland cement (nasty blue-gray stuff) is only on the areas that have failed. The areas on the left of the photo that have only lime mortar are in worn, but reasonably good condition. That dusty hole where a brick used to be in the middle is called spalling, which is what happens when water a) freeze-thaws inside a brick or b) builds up to such a high level of pressure it literally causes the brick to explode in slooowwwww motion.

To get around all this high-maintenance brick foolishness, another popular technique is to build the foundation out of something that’s unlikely to wick- like stone. Stone is strong, hard, generally impermeable (though mortar is definitely permeable), expensive, and a pain in the ass to lift higher than one’s head.  So, build the wet parts of a building out of stone and the upper parts out of easily-maneuvered brick or timber. The example below is the Lock Keeper’s House in Maidens, VA- built on a low floodplain next to a canal lock, so there’s lots of water around.


So there’s a basic summary of how water goes up, and we all know how water goes down. Except perhaps Le Corbusier- as lovely as the Villa Savoye is, the damn thing leaks like a sieve because flat roofs don’t shed water. Tune in next time for how our ridiculous obsessions with climate control and indoor plumbing created ways for water to come FROM ALL SIDES. Oh, the humanity.



One response to “Preservation 101: Water is a B****

  1. Pingback: The Sad Strange Story of Richmond’s Libby Prison | buildings in your history·

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