Shingles usually occurs in about 3 steps. First, the rash has not appeared and the person usually experiences flu-like symptoms. The next stage, the rash still has not appeared, but the person feels the pain, itching, and tingling in the area where the rash occurs. Lastly, the person forms the rash, first blisters and then crusting. A person who has shingles can only pass along the virus when the rash in the blister phase. After the rash has developed crust, then the person is no longer contagious. It takes about 2-4 weeks for the rash to go from the blistering phase to the crusting phase. To read more about the stages of shingles, click here.


Shingles is less contagious than chickenpox and the risk of someone spreading shingles when the rash is covered is very low. While your shingles is in the blister phase, it is best to avoid pregnant women who have never had chickenpox, infants, and people with weakened immune systems because these people are at risk of getting chickenpox.
Sources:
http://www.healthline.com/health-slideshow/shingles-pictures
http://pathwayshealth.blogspot.com/2013/02/shingles-overview.html
http://www.cdc.gov/shingles/about/transmission.html
http://www.livestrong.com/article/107700-early-stages-shingles/