ICS Magazine

Inspecting Wall Cavities for Mold

June 15, 2004
Containment systems are crucial components.


Q: The S520 highly recommends that I perform an inspection of the property so that I can make a preliminary determination of whether or not there is mold growth. How can I inspect inside wall cavities without contaminating the air?

A: To make the preliminary determination of whether or not there is actual or potential mold growth, the remediator may want to inspect wall or other structural cavities as part of the inspection. There are a number of ways this can be done without releasing contaminants.

Every situation is unique. If, during your information gathering and building inspection, you have a visible mold problem on a wall surface as a result of it being chronically wet, you can assume there is mold growth in the wall cavity. Opening the wall cavity to perform an inspection does not make sense. If the wall has mold growth, it is going to be removed anyway.

On the other hand, you may have a chronically wet building with no visible mold. You can either assume that mold exists, or else you can perform an intrusive inspection in an attempt to make that determination.

It is important that you approach intrusive investigations gradually. For instance, don't, as a first step, pry off a long section of baseboard to see what is behind it. Instead, use a flat pry bar at an appropriate point to slightly dislodge the baseboard just far enough away from the wall to see what is behind it. If you see what may be mold or other microbial growth on the drywall behind the baseboard, stop. Don't proceed until you have set up appropriate engineering controls.

Another example of this graduated approach is to first cut a small hole into the cavity. Look at the back of the gypsum board plug as you remove it. If mold growth is present, the plug can be reinserted and sealed in place. If the small hole turns out to be inadequate, you may need to make it larger. Never cut an opening larger than necessary to determine what you need to know. Generally speaking, a smaller hole will release a smaller amount of contaminants. Flashlights and lighted, angled mechanic's mirrors are helpful to more thoroughly examine the interior of the cavity. This is especially useful for exterior walls where you may need to look at the back of the gypsum board you have cut through.

A very small hole (1⁄4 inch to 1⁄2 inch) may be adequate to investigate a wall cavity when using a flexible or articulating borescope. These devices are available starting at about $250. High-quality articulating borescopes with photographic or video capability start at about $2,000.

Whenever you cut or drill a hole into a wall surface, it is helpful to hold the intake of a HEPA vacuum close to where the hole is being cut or drilled. This captures the dust created by cutting and contains any contaminants that might otherwise be released. Air-filtration devices have a capture zone on the intake side. This is the area where 100 percent of the dust and contaminants will be collected by the HEPA-filtered unit. If you locate the AFD within a few feet of the area that you are investigating, you can open cavities within this capture zone. Any contaminants released will be immediately drawn into the filters of the AFD. A smoke pencil or tube is very useful in determining the size and shape of the AFD's capture zone.

HEPA vacuum cleaners may also be used to filter the air when depressurizing an entire wall cavity. Using a hole saw, cut a hole through the drywall, slightly larger than the outside diameter of your vacuum hose, in the area adjacent to where you intend to investigate, but below any fire blocking. Plug the HEPA vacuum hose into this hole. When you open a small hold at the bottom of the wall, any dust or contaminants released are sucked up into the HEPA vacuum.

Using this technique is quite adequate for interior walls. Exterior walls, which contain components such as insulation and vapor-retarding barriers, usually require a considerably larger opening. To prevent escape of contaminants through this larger opening, a more elaborate containment system may be needed. The two main types are temporary containment systems and mini-containments.

A variety of temporary containment systems are available. Poly sheeting attaches to these extension-pole systems to quickly erect temporary containments. Most of the temporary containment systems are less sturdy than more permanent types, but for investigative purposes they may be adequate. A temporary containment should be negatively pressurized, using either a HEPA vacuum or a small AFD on low speed to avoid collapsing the containment system.

The highest degree of containment you are likely to need for investigative purposes is a full-fledged mini-containment. Frames can be assembled from various materials including, but not limited to, electrical conduit, 2-by-2s or 2-by-4s, or PVC pipe. In most cases, remediators are using 11⁄4-inch PVC pipe with 3-way tees at the corners. Lightweight and inexpensive, it is easily cleanable and therefore reusable.

Purchase eight 3-way tees and six 10-foot lengths of pipe. Cut four of the pipe lengths at 6 feet 8 inches. Cut the other two lengths into thirds of 3 feet 4 inches each. Assemble the eight 3-way tees, four uprights of 6 feet 8 inches and eight horizontals of 3 feet 4 inches into a box frame.

Wrap this frame in 4- or 6-mil poly sheeting and install appropriate Z-flap or double/triple flap doors. A zipper door, properly installed, may be efficient for this use. This chamber, when assembled, is about 7 feet high and 4 feet square. It is just about the largest size that can be turned from a horizontal to a vertical position in a room with an 8-foot ceiling. Being able to do this can make assembly considerably easier.

The most efficient way to negatively pressurize the mini-containment is with a HEPA vacuum. This is especially convenient since you need a HEPA vacuum to clean the containment interior anyway.

Place the vacuum outside the mini-containment, running the hose inside through a small slit in the poly sheeting. A 100-cfm vacuum will provide more than 50 air changes per hour in the mini-containment described here. If the mini-containment is sealed to the wall surface reasonably well, the HEPA vacuum will create negative pressure that is more than adequate to prevent contaminants from escaping.

Using a mini-containment, the investigator should always be sure to use appropriate personal protective equipment. Assemble the mini-containment and install HEPA vacuum as described. Cut flaps in the poly on the side facing the wall you are investigating. Using tape, seal these flaps to the wall surface. Turn on the HEPA vacuum and enter the mini-containment, making sure that the doors seal well behind you. Check for negative pressure by making sure that the poly is drawn in by the HEPA vacuum. Open the wall cavity and investigate as appropriate.

If contaminants are found, seal the cavity back up to prevent any release. Thoroughly clean yourself, any personal protective equipment that will be exiting the chamber (including your respirator), and the interior of the mini-containment. Disassemble the mini-containment, disposing of the poly sheeting and contaminated materials. If contaminants were found, leave the cavity sealed while appropriate steps to deal with the mold problem are discussed with interested parties.