Backing bar – Designates the backing bar to be used on the back of the weld.Surfacing – Specifies the welds that are made over the entire surface of the piece.Melt-thru – Indicates that the root of the weld needs to be reinforced.Something like giving the weld a good back. The back weld on another hand goes after the actual weld. The backing weld is deposited before the actual weld in the groove.
While I highly recommend you read it all and see all of the images, here is a handy small table of contents that links to the top sections of the article: If you don’t have the time or you don’t have an internet connection at your workplace you have a free downloadable PDF file (e-book) with all the welding symbols and their short explanation. This is a Massive article with well over 4000 words, over 50 subheadings, and symbol drawings. We break down all the important pieces about this topic right here. If your goal is to become a pro one day (read bigger salary!), then you better sit down and study. It might be for amateurs, but professional welders have to have exact knowledge about welding symbols. Some people think that just knowing the welding process is enough.