  Ab initio calculations are performed to study consecutive reconstruction of a
zigzag graphene edge. According to the obtained energy profile along the
reaction pathway, the first reconstruction step, formation of the first
pentagon-heptagon pair, is the slowest one, while the growth of an already
nucleated reconstructed edge domain should occur steadily at a much higher
rate. Domains merge into one only in 1/4 of cases when they get in contact,
while in the rest of the cases, residual defects are left. Structure, energy
and magnetic properties of these defects are studied. It is found that
spontaneous formation of pairs of residual defects (i.e. spontaneous domain
nucleation) in the fully reconstructed edge is unlikely at temperatures below
1000 K. Using a kinetic model, we show that the average domain length is of
several $\mathrm{\mu}$m at room temperature and it decreases exponentially upon
increasing the temperature at which the reconstruction takes place.
