How long does take for untreated gerd to cause barrets esophagus ?

Many years: It is a slow process, taking upwards of 10 years. Most people with GERD never develop Barrets

Varies: Gerd of some sort is in 10-20% of the population (maybe slightly higher). Barretts' is about 1/10th that common http://www.ncbi.nlm.nih.gov/pubmed/16344051 so... most never get it.

Chemical burn: Reflux, chemically burns the lining mucosa of the esophagus.......which is not acid resistant. Recurrent and prolonged process changes this epithelium to abnormal.....Barret's