Mold remediation has its own IICRC standard — the S520 — and it exists largely because mold work has a unique way of going wrong: done carelessly, the remediation itself can spread the very problem it's supposed to fix. Understanding the basic shape of S520 makes it a lot easier to tell a careful job from a rushed one.
Assessment comes before removal
S520 starts with identifying the moisture source feeding the growth, because remediation that removes mold without fixing what's feeding it is remediation that fails again shortly after. It also calls for classifying the condition of the affected area, which determines how the work needs to be contained and performed.
Containment is the part that gets skipped by shortcuts
This is the piece that matters most and gets skipped most often. S520 calls for engineering controls — physical containment barriers and negative air pressure — to keep spores disturbed during removal from spreading into unaffected parts of the home. Cutting into moldy drywall without containment doesn't just fail to fix the problem; it can actively spread contamination into rooms that were clean before the work started. A remediation job without containment can make a contained problem into a whole-house one.
Removal and cleaning follow the condition, not a one-size-fits-all method
Porous materials with significant growth (drywall, some insulation) are generally removed rather than cleaned, since mold grows into the material itself.
Semi-porous and non-porous surfaces are cleaned and treated using methods appropriate to the surface and contamination level.
Air scrubbing with HEPA filtration runs during and after the work to manage airborne spore levels.
Verification is the step that confirms it actually worked
A properly run job doesn't end with removal — it ends with a post-remediation evaluation: a visual inspection confirming no visible growth or moisture remains, and in some cases third-party clearance testing to independently confirm the space meets acceptable conditions before it's considered complete. That verification step is what separates "we think we got it" from "here's confirmation we got it."
What to ask before hiring
It's reasonable to ask a company directly: will you contain the work area, and how will you verify the job is done when you're finished? Those two questions get at the heart of S520, and a company that's actually following the standard will have a clear answer to both.
Expert Restoration LLC runs every water, fire/smoke, and mold job to IICRC standards across Thurston, Mason, Lewis, and Grays Harbor counties. Call 360-480-7540 for a documented, standard-based assessment.