Our home, that we had built 2 years ago, had a leak under the slab. Once the plumber opened the floor he found a leak and the copper pipe had green spots all over it. What could these spots be caused by and should we worry about future leaks?
I've always been told that copper was so much better than any other material for plumbing that there was almost no comparison. However, since I've been repairing plumbing in homes for the last 30 years or so and have had to remove hundreds of chunks of copper pipe from inside walls that have corroded, with the green patches you're talking about, until they've developed small leaks which then turn into big leaks, I won't plumb anything that's going to be inside or under or above anything else, with copper. I use either Pex, or CPVC or galvanized iron pipe wheneven it's going to be a hidden application. That way I can be sure that it's not going to leak in the future. I'd never put copper underground or in cement. I've had to dig way too many pipes up with a hammer and chisel to do that to anyone else.
Copper pipes are connected by soldering them together. The soldering process requires application of an acid flux to remove oxidation from the copper during the soldering process. It is likely that whoever did the soldering left some acid residue on the surface of the copper. Over a period of time, the residue promotes corrosion. Copper turns green when it corrodes. It isn't a problem, but if you want to eliminate the green, use an abrasive Scotch Pad and a mild soap and water solution. Rub the copper pipe with the pad dipped in the soap water. It isn't a lot of work, but the copper pipe will be very bright when finished. The remaining pipe that you don't scrub will be dull. Rince when finished and the green should not return.
Oxides of copper are all green. Any copper exposed to the environment will oxidize and eventually will turn greenish. The reason why SOME copper does NOT oxidize is because it is coated with a clear plastic or paint, which separates the base metal from the air and means no corrosion. The same applies to every metal. All metals form oxides on the surface. Some metals like iron and copper are obvious as you can see the oxide after a while. Others like gold, not so obvious. The oxide layer is either tightly bound and separates the base metal from the environment or porous which does not separate the metal from the environment. Gold is tightly bound and so thin you can see through it. Red rust is porous. Copper is sort of half way in between, forming a semi-porous layer which after a while gets thick enough to separate the metal from the environment and stop the corrosion from going any further, like applying several layers of paint when one layer or two is not enough to cover the existing color. ALL copper buried in the ground is coated to prevent corrosion. In your case, that coating was damaged in places, and everywhere it was damaged, copper oxide formed and turned the damaged spot green. Someone, probably not a professional as a professional would KNOW to be careful of the coating, was not very careful when installing the copper pipe, so it is possible you should worry. If you look closely, I'll bet you see actual damage to the copper under the oxide where it was dinged or scraped in some manner.
