We are preparing our house to put it up for sale. Our realtor told us to take down the ivy that was growing up the brick and siding. Well we did as told and now we have this gunk left on the siding from where the ivy clings to the wall. We have tried power washing, elbow grease, Simply Green and bleach to no avail.
Try TSP, or tri sodium phosphat. It should work on brick or aluminum or vinyl siding. It comes in a tub and has directions for mixing with water in a bucket. Scrub with a stiff brush.
If that doesn't work, what I think you have are the "feet" from the tendrils of the ivy. The feet must have some type of glue, so you need a solvent. If TSP doesn't work, try acetone (nail polish remover) or rubbing alcohol to get those feet off.
I used Dawn dishwashing detergent and it seemed to loosen the bond to the surface. Works best if the ivy is not dry.
Try steaming it and then lightly brushing it away. It worked for me!
I have painted bleach on ours, and it did work. I tried everything known to man, and this at least hid the color, but not the texture!