If you suspect asbestos in the mastic, simply take some precautions while working within the area. First, try to contain everything to the room you are working in: Install plastic over the floor in the area, then install plastic over the door opening from the top all the way to the floor and tape the seams if possible. Then, set-up a fan to create negative pressure and suck-out any dust. You can also spray down the area with water to keep dust particles down, and finally use a dust mask. Most of this is precautionary and is the right thing to do. However, the mastic shouldnt be dusty or crumbly. Regardless, the key is to minimize the spread of the dust of the materials and contain it within the work space. With a little common sense and forethought, you can avoid bringing in people in "space suits" to rid your room of potential asbestos. Oh yeah, when your done, roll-up the plastic covering the door, down to the plastic on the floor, then roll up the plastic on the floor. This will save you time on cleanup. Then, use a damp mop to clean up and remaining dust and debris. Avoid vacuums, unless they are equipped with a HEPA filter....most vacuums will spread dust to some degree, which is what you are trying to avoid.