How To Find Mold Behind Walls First, you need to figure out where you need to be testing, which is either: 1: Any wall that had a historical water intrusion and hasn’t been remediated OR 2: Any wall that is showing signs of water damage Once we know where we need to be testing, we use what are called cavity samples. We do NOT just use air samples in the middle of a room. HUGE no-no ❌ Cavity samples pull the air from behind your wall and tests that specific area. This allows us to be as accurate