If mold is confined to an open area and covers nine square feet or less, it's generally safe for self mold removal. Anything bigger than 3 feet by 3 feet or involving hidden mold (behind wallpaper or under carpets) is best left to the professionals. Expert mold removal should also be sought if repeated attempts at self-removal don't work or if any building occupants have asthma or other breathing difficulties that may be worsened by mold.
Before hiring a professional, make sure they have extensive experience in mold cleanup. If the water causing the damage is contaminated, make sure they have experience specific to that problem, too. Request references and follow up with phone calls. Find out what guidelines the company follows and what steps will be taken in the removal process. Guidelines should be from governmental or professional organizations, such as the EPA's Mold Remediation in Schools and Commercial Buildings .
What the company will do
Although different professionals will handle mold removal in their own tried-and-true way, there is one thing all will do. If the mold problem is big enough, they'll isolate the affected area with plastic sheeting, taping edges to the walls and ceiling to prevent the escape of mold spores. Occupants should stay clear of the rooms adjacent to the one being cleaned or, ideally, should try to be out of the house during mold removal.
Cleaning up the mold only solves half the problem. If the water leak or moisture issue that caused the initial growth isn't identified and remedied, the mold will grow back. Find out if the company or contractor dealing with the mold will also be able to find and fix the source of the water. You may have to call in another specialist before or after the cleaning to perform necessary fixes.
Beware mold-removal scams
Try not to choose a mold-testing company that also does mold-cleanup work. It's not to say they are all trying to scam homeowners, but you'll have a much better chance of getting accurate test results if the company limits its involvement to testing. Be on the lookout for practices that don't sound right, such as using ozone generators, ask a lot of questions and look to government resources if you're unsure of anything.