What Happens During Mold Remediation

What are the stages of a typical job?

Every company words it a little differently, but a well-run residential job in Seattle tends to move through the same stages in roughly this order:

1. Assessment: locate the growth, measure moisture, and trace where the water comes from.
2. A written scope and price, so you know which materials come out and which get cleaned.
3. Containment and protective gear sized to the amount of growth.
4. Removal and cleaning of affected materials.
5. Drying the structure and correcting the moisture source.
6. A completion check, ideally by someone who did not do the removal.
7. Rebuilding: new drywall, insulation, flooring or paint.

The sections below walk through what each stage should involve and what to ask about along the way.

How does the assessment work?

A good assessment spends more time on water than on mold. The person walking your house should be using a moisture meter, looking at framing and sheathing, and asking when the staining first showed up. Around Seattle the usual culprits are a slow plumbing drip inside a wall, a roof or flashing leak, condensation from a bath fan that vents into the attic instead of outdoors, groundwater seeping through a hillside foundation, or a vented crawl space that stays damp from October through April.

Hidden areas matter. If the stain on your ceiling sits under an attic, someone needs to get up there; if the floor smells musty, someone needs to go under the house. An independent mold inspection is the usual way to get this mapped before anyone starts cutting, and it is especially useful in older homes where the crawl space under the floor or the attic above the bedrooms may hold more growth than the room you noticed first.

Is lab testing part of the assessment?

Not always. EPA says that in most cases, if mold is visible, sampling is unnecessary, and there are no EPA or federal limits for mold or mold spores to compare results against. Washington DOH makes the same point: in most cases you can see or smell mold, and even a clean, dry house has some spores. Sampling is more useful when growth is suspected but hidden, or at the end of a job to show an area was cleaned properly. Our guide on whether paying for mold testing makes sense covers when lab work earns its fee.

What should the written scope include?

Before work starts you should have a document listing the rooms and square footage involved, which materials will be removed versus cleaned, the containment and air-filtration plan, how the moisture problem will be addressed (or who is responsible for it), and how completion will be checked. Washington L&I's Hire Smart guidance applies here as it does to any home project: get written bids from several contractors, make sure the price includes sales tax and payment terms, put any changes in writing, pay as phases are completed rather than all at once, and ask for lien releases before the final payment.

Washington has no state mold license or certification. DOH notes that anyone can call themselves a mold remediation specialist, and that voluntary training is available through groups such as the IICRC. What the state does require is that anyone doing construction or repair work on a building be registered with L&I as a construction contractor. You can check that registration, plus workers' comp status and any bond claims, on L&I's Verify a Contractor tool. Our walkthrough on vetting a mold company in Washington goes further.

What do these jobs cost here?

Angi's Seattle cost guide reports an average of about $1,988 for mold remediation, with most jobs between $1,008 and $2,967. Location in the house drives a lot of the spread:

The same guide puts most pros at $10-$25 per square foot and labor at $75-$120 per hour. Access, the number of rooms, how much material has to be thrown away, and how much containment is needed all push the number up or down. The Seattle mold removal cost breakdown has more detail.

How is the work area sealed off?

Containment keeps spores and dust from drifting into the rest of the house while moldy material is disturbed. EPA's remediation guide for larger buildings, which many residential companies use as a reference, scales containment to the size of the problem:

• Under about 10 square feet: usually no formal containment, but the person cleaning wears at least an N-95 respirator, gloves and eye protection.
• Roughly 10 to 100 square feet: limited containment, meaning a single layer of 6-mil fire-retardant plastic sheeting, sealed vents and doorways, and the area kept under negative pressure so air flows in rather than out. Workers move up to a half- or full-face respirator with HEPA cartridges and disposable coveralls.
• More than 100 square feet, or any case where occupied rooms could be contaminated: full containment with two layers of plastic and an airlock or decontamination chamber, and heavier respiratory protection.

EPA calls these thresholds guidelines, and professional judgment can call for more containment around a small but heavily affected spot. EPA also warns against running a heating or cooling system you know or suspect is contaminated, since it can spread mold through the building. If you heat with forced air, expect vents in the work zone to be sealed.

What happens to the moldy materials?

This is the part most people picture, and it is more about sorting than scrubbing. Hard, nonporous surfaces such as metal, glass and sealed tile can usually be damp-wiped with water and detergent and dried quickly. Porous materials are different: EPA notes that ceiling tiles, carpet and similar materials may have to be thrown away once moldy, and wet drywall with growth on it is commonly cut out. Removed material is double-bagged in 6-mil plastic before it leaves the containment. Framing lumber with surface growth is often cleaned and dried rather than replaced, depending on its condition.

Once materials are dry and debris is out, HEPA vacuuming picks up settled dust inside the work area and along the path out of it. Two practices to question if you see them: EPA's guide says bleach is not recommended as a routine part of remediation, and EPA's home guidance says not to paint or caulk over mold. A coat of sealer over damp, moldy wood hides the problem without fixing it. If the growth turned out to be inside a wall cavity, our page on mold behind drywall explains what opening a wall usually involves.

Why does drying and moisture control come before rebuilding?

EPA's position is blunt: the key to mold control is moisture control, and if the water problem is not fixed the mold returns. Both EPA and Washington DOH advise drying water-damaged materials within 24 to 48 hours, and EPA suggests keeping indoor humidity below 60 percent, ideally between 30 and 50 percent.

In this climate that often means work beyond the mold company's scope: rerouting a bath fan duct to the outside, adding a vapor barrier or improving drainage in a crawl space, repairing roof flashing, or fixing a supply line. Ask who is handling the cause and when, because closing up a wall before the source is fixed only resets the clock. Window and wall condensation through a long gray winter is its own problem, covered in our guide to condensation in Pacific Northwest homes.

How do you know the job is finished?

EPA lists several signs that remediation succeeded: the water or moisture problem has been fixed, no visible mold, mold-damaged material or moldy odor remains, any sampling shows indoor mold types and levels similar to outdoors, and a later visit shows no new water damage or regrowth. EPA also admits the final call is a judgment call with no easy answer.

No Washington rule requires the company that tests to be different from the company that removes, but Angi recommends separate companies so the person signing off has no stake in the result. That is the role of clearance testing after remediation: a visual check plus, where it helps, surface or air samples taken before the plastic comes down.

What does the rebuild involve?

Remediation companies often leave the space open, dry and clean, and the finish work is a separate line item or a separate trade. Angi's Seattle cost guide lists typical related repairs at $825-$2,400 for drywall, $650-$2,150 for carpet and $175-$450 for flooring. Get these in writing alongside the remediation bid so the total is clear before you commit.

What should your household do during the work?

• Stay out of the containment area and keep pets and children away. EPA says people with asthma or weakened immune systems should stay away from moldy sites, and mold exposure can irritate the eyes, skin, nose, throat and lungs.
• Leave the plastic, tape and air machines alone, even overnight.
• Keep the furnace or heat pump off if its ducts run through the affected area, unless the company says otherwise.
• If anyone in the household has health concerns, talk with a health professional.

Job length varies with the size of the area, how fast materials dry in damp weather, and whether a plumber, roofer or drainage contractor has to come first. A single bathroom wall moves faster than a crawl space under a 1920s house. If you are ready to line up a mold remediation company in Seattle, or you live on the Eastside and want remediation help in Bellevue, the same sequence applies. South Sound homeowners can start from our Tacoma page.