Asbestos would be difficult to see in plaster

[KBCampbell]

I’m no expert in this area but if you’re able to separate the fiber strands into soemthing the size of hair then its doubtful its asbestos. What makes asbestos dangersous is the very small size of the fiber which, in the lungs, is too small to be expelled by the lungs’ self cleaning ability. But apparently asbestos was used in a lot of building applications. View this: http://enviro.nfesc.navy.mil/esc425/AsbInBlg.htm

I’ve seen horsehair used for binding in plaster in older homes before but it was coarse and black in color.