Maybe at one time that concrete was sealed and that is the old sealer showing ?....
Ray Burke said
Aug 4, 2014
Jeff: the metal on the sign pole is leaching out metals that are killing the growth on the concrete.
Jesse Bracken said
Aug 4, 2014
Galvanic coating is a process where Zinc is applied to metal to protect it from corrosion. Zinc is added to algae resistant shingles (used to be copper, but it got too expensive) There fore the Zinc is killing the what ever is growing on the concrete as it leaches off the sign post.
Jesse Bracken said
Aug 4, 2014
oops sorry I didn't see Ray's response till after i posted...
Jeff Thompson said
Aug 4, 2014
Ray Burke wrote:
Jeff: the metal on the sign pole is leaching out metals that are killing the growth on the concrete.
Interesting. I was focused on all the spots away from the pole. They are everywhere. Didn't think they could have spread out like that from the pole.
Troy Layman said
Sep 26, 2017
Yay me! I knew the answer. Good info Jesse. I didn't realize that about the AR or stain guard shingles using zinc instead of copper due to the cost. I guess I haven't read every post on these forums yet.
Can anyone tell me what is causing this unique stain patter on the concrete?
Jeff:
the metal on the sign pole is leaching out metals that are killing the growth on the concrete.
Interesting. I was focused on all the spots away from the pole. They are everywhere. Didn't think they could have spread out like that from the pole.