Home & Garden Columns

About the House: What To Do About Mold Spores in the House

By Matt Cantor
Friday May 11, 2007

There are few things in life as embarrassing as having to ask your hostess what’s in the casserole. I know. I’ve been doing this for the last 15 years or so since having finally figured out after many distressing years that I’m not good friends with bovine products. 

Not meat, mind you. I do fine with beef, although, like most of us, I’ve pushed that plate pretty far away in favor of tofu and fish. No, it’s the other wonderful things that cows will gladly give us in return for their lives: Cheese, milk, cream, ice cream and sadly, butter. It’s not really as bad as it sounds. I’ve gotten used to it and the downside for me personally was so distressing that I need only remind myself of the late night wheezing or stomach ache to happily eschew the Cheese Board pizza.  

Of course, there is that issue of the dinner party at Ben and Lisa’s where I actually have to ask if butter is used in the casserole. I just hate it. So when I talk with mold sensitive clients, and this IS something that comes up with some regularity, I have more than a little empathy for those who cannot live with what others take for granted. 

You see, that’s the funny thing about mold, mildew and other fungi. They’re all around us, on everyone’s menu but some folks have a very hard time with them. My own dairy sensitivity is nothing compared with, for example a serious peanut allergy. Some folks can’t eat food that was prepared using the same machine that grinds up peanuts and will go into shock over the tiniest exposures. 

This is also true with molds and mildews. While most people can eat cheeses cultured with mold (funny you should ask), tempeh and the other moldy foods we eat, a few sorry souls are exempt and must eschew, not chew. 

So when we talk about mold in buildings, it’s the same. Molds and their neighbors (members of the fungus family) are common to our environment and, in typical settings, are not significantly pathogenic (unless your immune system is compromised, in which case many common molds can become a serious threat). 

The one thing that almost all molds have in common is their need for moisture, although many need other conditions (like still air) to propagate successfully. So, the first thing that I start thinking about, when I’m confronted with a mold or mildew problem, is where the wet is coming from? If you do, as I do, you begin by opening a toolbox of investigative and amelioratory tools. 

Let me give you that toolbox (or at least a beginner’s set) so that you can go boldy where no aspergillus has gone before. 

Since we know that most molds require fairly high levels of humidity to grow, our first tool is a simple examination of the external shell of the building. If there are physical signs of growth in one particular place and not in others, we have a big clue. Later we’ll discuss broadcast effects. 

If I have one closet or one bedroom where there is growth and it’s all localized along one wall, I’d start by examining the walls and adjacent surfaces. A closet is more likely to be a problem because of still air, which spore-producing critters prefer. When they get blown about, they have difficulty propagating. The simple act of opening a closet can lessen the growth of a mold colony. 

I will want to make sure that there is no leakage into the interior of walls or into the living space from the outside so a good set of eyes working slowly across the roof and exterior is the first major tool to use when it’s clear that the growth is discreet or localized. If you take your time, this can be quite effective. 

Keep in mind that water can enter through a fissure one-8000th of an inch (or so I’ve been told), so it’s critical that all junctions on the exterior of the house be sealed or configured to shed water outward. On the inside, signs of moisture aren’t hard to detect, although a moisture meter can be quite handy. 

If you don’t have a clear sign of leakage from roof or wall, and growth is randomly noted, it’s possible that you’re dealing with elevated moisture levels due to ground moisture. Moisture travels from cold to warm because warm air will hold more moisture than cold air (counterintuitive, I know) so this is why moisture will travel up out of the soil or damp basement to the upper areas of the house or the outside walls. 

Area which have elevated humidity or actual dampness on surfaces will tend to grow bushes, grass, corn or maybe just mold. Mold spores are all around floating in the atmosphere and they need only find a damp environment to begin having large families. 

The second set of tricks or tools relates to this condition. If we have a good idea that the moisture started in a soil-surfaced crawlspace (as opposed to a basement), the first and cheapest thing to do is to cover the soil with plastic. A “vapor barrier” does not need to be sealed at the edges or taped together, although these things certainly can’t hurt. 

Steve Quarles, of U.C. Berkeley, has shown us in his research that moisture levels in crawlspaces are driven down very effectively by nothing more than laying plastic on the ground. So, this being the case, it’s the first thing I’d do if I believe that this was happening.  

The other thing that can be done if damp soil is the source of moisture is to increase ventilation in a crawlspace so that air can naturally dry out the soil through increases evaporation. 

Breaking the barrier between the crawlspace and the exterior allows the two spaces to reach equilibrium and it’s often a lot wetter under your house than it is outside where the sun and breeze are drying things out. 

If you’re not sure if the inside of your house is damp, a great tool to acquire is a hygrometer. Cigar stores carry these and they’re pretty cheap to buy. I see them on eBay for 10-20 bucks all the time. If you put this up in your living space and study it over a course of days, you’ll be able to get a sense of how damp you’re home is. A moisture level of 40-60 percent is very nice but a moisture level of 90 percent is probably going to lead to all night fungus parties at your place. 

A tool that is both diagnostic as well as amelioratory is a dehumidifier. You can set one of these in a room and within a day or two figure out if the room was really damp. If the unit is collecting buckets and buckets of water and never shuts down (they have adjustable “humidistatic” controls), it means that there a lot of water in the space and you’ll probably want to start taking other measure.  

Nonetheless, leaving one hooked up and hosed to the outside, can actually fix a damp space, although I’d never choose that as my final solution. I’m too cheap to want to pay the electric bill and dehumidifiers cost money to run. 

If you’ve got major wetness in the subfloor area (i.e. boat ramp, fishing pier) you may want to install a subsurface drainage system. This can help to dry things out but costs a lot of money and is never my first solution. That said, there are houses for which this IS the solution. Even then, some will need additional ventilation, vapor barriers and other tactics. 

So this is the short course and not, by any means a complete assessment of what makes mold grow but, seriously, these few tactics can help I.D. or lessen the ill effects of damp wood and plaster in many homes. 

If you’re someone who’s clearly getting sick, don’t mess around. If you can’t make things better in very short order, just get out. There’s always another place to bed down and being sick isn’t worth staying at Buckingham Palace. I’m lucky. Like most people, I can live with a little damp and a little mold but when it comes to lunch, I’ll take the sushi and leave the pizza for someone else. 


Got a question about home repairs and inspections? Send them to Matt Cantor at mgcantor@pacbell.net.