What It Means To Dry

Where does water go when it dries? This sounds like a replacement line for Nirvana’s cover-song “Lake of Fire,” originally written by the Meat Puppets (who knew…). But seriously, where does it go?

As home inspectors, building consultants, homeowners, trades professionals, we all have this magical understanding related to things drying. But, what really happens when something dries and how might it be important to our understandings of our modern-day huts? Strap on the old thinking cap because we’re on a reading rainbow journey!

Let’s take drying clothes as an achievable example: We pull the clothes from the washing machine and hang the delicates to dry. How is this happening? We feel the clothes wet when they come out of the washing machine drum, so we tangibly know the water is there. But, then we hang them and poof, the water isn’t there…but also isn’t anywhere else we can see. Evaporation.

Okay, so maybe you’re thinking I’m new to this world. But, no. You can’t just say, “It evaporated.” What does that mean? Can you say? Most can’t. So let’s: Evaporation would be the process where a tiny mouse wizard comes behind us when we leave the room and waves a wand around, chants some very indiscernible words, and creates just enough energy (think megajoules per kilogram) to disperse the bonds of the water molecules near the surface. These molecules are henceforth not a liquid, but a gas and then, like all well-meaning gases, leave to play pickleball, go see an over-priced movie, or get their hair blown out. Eventually, they will get lonely and re-congregate into a nefarious fluffy cloud and phase change back into a liquid. They could also re-appear as condensation…depending on several variables.

This is Fred. He’s pretty busy drying all our clothes.

As a side bar, as those water molecules nearest the surface change phase and evaporate, water molecules left behind take their place (more on this below) at the surface, and then, they too evaporate and disperse if conditions are proper. And thus, eventually, we get “dry.”

So, maybe ditch the magical mouse and wand, but the energy part is true. The thing is, the required amount of energy to “dry” depends on several factors we shan’t be including herein. Now, the key for us in the built environment is what often gets phrased as “the drying potential.” This is not the same as “college potential,” though both could prove to be unexpectedly expensive. While we may not need to worry about how our plasticized briefs and bras air dry (there’ a reason many of our undergarments come with warnings to avoid excessive heat), we should be concerned with the drying potential for moisture in the materials that make our fancy huts.

Seriously, if your undergarments aren’t cotton, look at the packaging and/or labeling. Most have a warning to stay away from heat sources…

You see, in my glorious 1940 home, any water that adsorbs onto or absorbs into the board sheathing will diffuse readily along the grains (wood in particular) and eventually evaporate/dry out with minimal effect because my home has great drying potential due to being poorly air sealed and insulated (please, send me money in lieu of medals for this amazing accomplishment…it can help me pay my utility bills). But, in some homes of various vintages, inclusive of modern builds and commercial applications, there is LESS drying potential due to modern configurations of our wall assemblies and building materials (that is, those areas that get wet don’t necessarily have access to the energy needed for evaporation because energy is being properly sequestered within the home’s interior habitable enclosure). This is not a bad thing, if you care about the status of the environment or your bank account. It IS a bad thing, however, if you want your walls to not be a terrarium of mush that can’t stand up to wind and pests AND you build without paying heed to moisture movement.

You know all those local news stories, social media posts, and leaflets dropped from above that focus on toxic mold in homes (side bar: such mycological toxicity is real and really, really bad where it actually occurs…that’s not every time, however)? Those highly credible news sources should be focused on how those fun guys (get it…) showed up to party in the first place. If we managed our assemblies better with a mind toward drying potential (read, evaporation), then it would be less frequent for these spores to rudely take over. I digress.

Yep, imagine these spores just waiting to party in your home’s walls, or ceiling, or crawlspace, or basement, or ductwork…well, anywhere where variables are conducive to their partying..

Evaporation. Okay. So, evaporation happens when water molecules near the surface gain enough energy (heat energy, temperature) to free their oppressive bonds. Then, diffusion (think about perfume being sprayed in the air) via physics disperses these from high to low concentration and hence they “disappear.” Again, remember that diffusion also is the reason one concentrated wet area spreads to less-concentrated dry areas during the stage of what we’ll call “water wetting” (this is named thusly because there’s another chemical process referred to “wetting” that I don’t want to confuse with our current topic). Without diffusion in the product/material, evaporation would not be possible – but, we’re talking about diffusion in a liquid phase first, then in a gas phase post-evaporation. Meanwhile, back at the farm, if your environment is really wet, or cold, the moisture in our proverbial materials, be they clothes or building supplies, will not evaporate as quickly because there isn’t enough potential energy and there may not be enough dry air for diffusing from wet to dry/more to less.

Very simplistically, diffusion is one of the things occurring in this photo…along with a jean vested bartender in the background…

There’s also osmosis. This technically isn’t the same as water drying, but it plays a role in the exchange of water from Point A to Point B. We won’t get into osmosis because it technically reverses the always high-to-low principle, but then it doesn’t because it isn’t about the water for osmosis – it’s about the sketchy people water hangs out with (solutes) and the need to dilute those 1980s Seattle-based punks. As an aside, osmosis can be the force behind the death of your brick and other masonry materials; the force is strong with this one. So, the next time you see spalling brick and efflorescence, you can thank me (again, send money).

Why does this truly matter for us as inspectors, builders, and consumers? Well, if you have a failure in a wall, roof, or floor assembly (use the same mental image of a rectangle, just rotate for each position), whether that failure results in catastrophic damage and fungal growth partially depends on the drying potential which happens via diffusion, evaporation, and diffusion. The longer organic-based materials (and non-plasticized composites) stay wet, the greater potential for degradation. And, in many of our regions, most trades professionals remain ignorant (in the truest sense of the word) related to building with a mind’s eye toward the physics of drying and so moisture gets “trapped” in the assembly components (assume Liam Neeson [heat energy/potential] can’t get to his daughters [moisture] to free them from the bad guys [the building materials]). If you read the fine print by many manufacturers who make these building materials, you will see they assume their products will get wet. After all, they are exposed on the exterior, which is outside. They provide instructions, configurations, and videos explicitly showing how to make sure said product(s) can be protected and/or can dry by not trapping water.

Seriously, the literature that accompanies materials can be very informative and valuable.

So, if you find evidence of something wet, it has at least one source and that source may or may not be readily obvious. Try to find it or hire someone who can. Remember – water, heat, energy, and pressure move from high to low, more to less. If you see something deteriorated from being wet, you can assume it doesn’t have the potential (energy) to dry via evaporation and diffusion because there are nearby variables askew for healthy conditions (or, it was exposed to moisture in a way that it was never designed to be…like composite cement cladding in direct contact with a roof/ground surface). Find them (the askew variables). When you can name “it” and “them,” you can put the puzzle pieces together, inform your client, and help the right people answer, “so what now?”