House detective: moisture meters sniff out trouble before it grows

Tools of the Trade, Sept-Oct, 2004 by Bob Rudd

I built homes for 15 years before closing up shop to focus on remediating moisture and mold incursion problems. While I have specialized moisture meters to cover every situation I face, I use two types of meters the most--surface and pin--and recommend them for builders to identify if there is a moisture problem, potentially a mold problem, and how widespread it is.

The surface meter works like a stud finder and can read about 3/4 inch deep. The pin meter reads much deeper by punching two small holes in material with sharp metal probes, which get behind or inside building materials like hardwood floors, trim, siding, or plaster. Moisture meters aid significantly in determining the size and extent of a moisture incursion and can provide the information necessary to help you determine if you can fix the problem yourself or if you must call a professional investigator.

Surface. I use a surface model, specifically the Delmhorst Accuscan, first because they don't punch holes. These units are best for "seeing" moisture behind a solid surface like drywall or ceramic tile, and are also effective for locating defective plumbing, condensation, or even standing water accumulated somewhere like in a ceiling. The surface meter delivers dependable readings in many situations, which it determines through measuring the resistance in the conductivity field between the pads on the sole of the tool. Note that pipes, nail heads, and corner bead can register on the meter, and they don't necessarily mean water is present, so double check by moving the meter to a dry stud bay nearby to get an accurate baseline reading.

While a surface meter can read through 10 layers of latex paint like in an old house or apartment building, this tool can sometimes get faked out by certain types of wall coverings, like vinyl wallpaper, stucco, EIFS, and thick coats of plaster. If you suspect leaks behind any of these materials, use a pin meter.

Pin. For reading to a greater depth below the surface, I use a Delmhorst BD-2100 pin meter, which provides the dependable readings I need to formulate an analysis of what's happening to a building. Pin meters are suitable for testing the moisture content of everything from framing lumber to concrete and stucco systems and are my go-to tools for getting really accurate readings in all kinds of materials. They're also effective for finding damp spots on, in, under, or behind other materials like gypsum board, carpet, hardwood floors, and plaster, but I use them mostly for testing baseboards. Not only can a pin meter tell me if a baseboard is wet, it can tell me how wet it is based on its Percent Scale. I know that if I punch holes in the baseboard and find a reading over 16 percent, there is a good chance mold could be part of the moisture problem (mold won't grow in moisture levels less than 16 percent). I also suggest using pin meters to make sure your framing is dry before you close it in with drywall--make sure it is less than 16 percent. I also use it to make sure wallboard is dry.

READING THE READINGS

If a customer calls and says they have wet, squishy carpets under a window (I get this call all the time), don't go into their house and immediately put the moisture meter on the wall in the wet area. Instead, go to a location in the house that you know is dry and establish a baseline reading with either type of meter. Once you have the baseline reading on the meter's Relative (or Reference) Scale, you can go to the affected area and start your investigation.

Most moisture settles in the bottom of the wall, so start searches at the base molding. Once the meter is reading the affected area, watch to see if the reading increases dramatically from your baseline measurement. Move the meter out and up from your starting point to determine how much of the base molding and/or wallboard is affected. Mark the boundary of the wet spot with colored tape. (Remediation experts always use red tape.)

The EPA says a wet spot less than 10 square feet--even if it has mold--is something you'll likely be able to repair yourself ("Basic Remediation Protocol," page 21). Anything larger and you should call a professional moisture investigator to determine the extent, of the problem and to write a remediation protocol. This is a key move that could save you major headaches down the road because, for a large intrusion that has been wet for more than 72 hours, it's likely that mold is present. The last thing you want to do is infect an entire house in a well-intended effort to fix it. If you attempt to fix it yourself, you could end up spreading the mold instead of eliminating it. Editors note: For more on mold, check out "God Mold?" on page 34

BASIC REMEDIATION PROTOCOL

List three phone numbers in your business directory right now: a moisture/mold investigator, a restoration contractor, and a mold remediator.

Which of these three you should call depends on the scope of the problem and how long it has existed. If a washing machine supply hose bursts and you respond within 72 hours, you'll need a restoration contractor to evacuate the water and dry the building. If there is mold, suspicion of mold, or the material has been wet for more than 72 hours, get an investigator. Upon finding mold, the investigator should refer a remediation contractor to do the specialized work of removing it.