Without wanting to start some kind of finger pointing argument, it seems to me that it would have been easy enough for the welder to lay down some fire blanket to keep the hot slag and sparks from marking up the deck. Simple and cheap.
Charles
Hello Mikehomeowner, any responsible welding contractor would know and take precautions to protect surrounding areas while performing welding on just about anything. I have worked for numerous contractors on both residential and commercial applications and in every instance we had to take precautions for the exact reasons that you have spelled out. Fire blankets are available to take care of welding sparks and prevent burns on surrounding materials, shields can be used to prevent grinding streams from pitting glass windows and other types of things, tarps can be put down to prevent paint overspray situations, it is unlikely that you will prevent all damage from occuring, however, you should expect that this damage will be minimal. In my personal opinion it sounds as though you should expect the contractor to take whatever measures are required to satisfy you in regards to the condition of the deck. You may end up in court depending on his response, if so, things are on your side as far as I can see. As a final note this situation would not be a common good practice for any welder. Good luck and regards, aevald