Plastic Walls and Air Scrubbers: How Mold Containment Keeps the Rest of the House Clean
Containment walls off the work area with plastic sheeting so the dust and spores from removal and cleaning stay put. An air scrubber with a HEPA filter runs inside and pushes filtered air out of the space, which keeps the work area at slightly lower pressure than the rest of the house. Air leaks into the containment, not out of it. HEPA vacuums do the cleaning. Together they're what separates remediation from spreading the problem around.
Cutting out moldy drywall makes a mess you can’t see. Most of the dust and spores that come off a wall during removal are too small to notice, and without containment they ride the air into every room in the house. The plastic walls and the humming machines aren’t for show. They’re the difference between fixing one room and spreading the problem through all of them.
Containment: the plastic walls
Containment is plastic sheeting taped and stood up to seal the work area off from the rest of the house. How much depends on the job.
For small areas, a single layer of plastic around the work, sealed at the floor and ceiling, with a slit or zipper door to get in and out.
For larger areas, the EPA’s mold course describes full containment: double layers of plastic, and an airlock or decontamination chamber between the clean side and the work side, where workers bag waste and clean up before stepping out.
In every case, the HVAC registers and returns inside the space get sealed, and the system is usually shut off while work is underway. Ducts carry dust everywhere, which is why the EPA warns against running a system that may be contaminated.
Negative air: why air leaks in, not out
An air scrubber is a box with a fan and a HEPA filter. During remediation it’s set up to pull air out of the containment, through the filter, and push it out of the containment, usually ducted outdoors. That leaves the work area at slightly lower pressure than the rest of the house.
Lower pressure means any gap in the plastic leaks air into the containment, not out of it. You can see it working: the plastic walls bow gently inward. On my jobs, I check it with a manometer, a gauge that reads the pressure difference across the plastic, so negative pressure is a reading, not a guess.
HEPA vacuums: the cleaning tool
A HEPA filter is built to trap very fine particles that ordinary filters pass right through. That’s why the cleaning is done with HEPA vacuums, not shop vacs. The EPA’s mold course recommends HEPA vacuums for the final cleanup. Why a shop vac isn’t the same thing is in the questions below.
The cleaning routine is HEPA vacuum, scrub or sand, damp wipe, and HEPA vacuum again. The whole job runs in that order, covered in how a mold remediation job actually goes.
What it doesn’t do
Air scrubbers don’t kill mold, and they don’t fix anything on their own. They control where the dust goes while the real work happens. Ozone machines and foggers are not the same thing, and they’re not a substitute for removal.
Where containment matters most
Homes where people are living around the work. Good containment is what lets you stay in the rest of the house. More on that in can you stay home during mold remediation.
Attached homes and mixed-use buildings. In a rowhouse, a twin, or one of the Old Town buildings with a shop below an apartment, the neighbor’s space is a wall or a floor away. Containment protects them too. Shared walls have their own considerations, covered in when the mold is on the wall you share with the neighbor.
How to tell it’s set up right
- Plastic sealed at the floor, walls and ceiling, with no gaps flapping open
- A zipper or overlapping flap door, kept closed
- HVAC registers in the space sealed
- An air scrubber running the whole time work is happening
- Plastic bowing slightly inward
- Bagged debris sealed before it leaves the area
If you see a crew cutting drywall with the door open and no machine running, ask why. And when the work is done, the containment stays up until the area passes its final check, covered in how to know a mold job is actually finished. That’s the standard my mold remediation is held to, and it’s what proper mold remediation in Gettysburg, PA looks like from the hallway.
Questions about containment and air scrubbers
Is an air scrubber the same as an air purifier?
Not really. A household air purifier filters the air in a room and puts it back in the same room. A remediation air scrubber is a heavier machine with a HEPA filter, set up to move air out of the work area, often ducted outside or into another space, so the containment stays under negative pressure. One is for comfort. The other is a control on where the dust goes during the work.
Why do you seal the heating and cooling vents?
Because the ductwork is the fastest way for dust to travel through a house. Registers and returns inside the work area get sealed with plastic, and the system is often shut off while the work is going on. The EPA's guidance is not to run an HVAC system you know or suspect is contaminated with mold, since it can spread spores through the building.
Can I use my shop vac to clean up mold?
Not for dry moldy debris. A regular shop vac or household vacuum blows fine particles right back out the exhaust. The EPA recommends HEPA vacuums for final cleanup once materials are dry and the moldy material is removed, and says wet vacuums should only be used while materials are still wet, because otherwise they can spread spores.
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