Closed Chimney painting, paint provided

• 2 years ago Surface to be painted: between 10 and 15 square meters (estimate).
  The small chimney sits on top of a two-story building. It is fairly easily accessible with ladders from the roof of the Burgh Hall in central Peebles, a solid flat roof which affords a 3-meter leg up to my own roof (pictures).
  For this job I will provide the masonry paint. Few other materials will be needed. Thus the work will mostly involve labour: no more than four hours for one coat of paint, seven hours for two coats. I will count travel time as labour. I will pay for all the labour cost (based on the tradesman’s advertised hourly rate and the length of time actually spent working), plus a 12% ‘completion bonus’, plus the cost of extra materials, if any. I think this is fair.