Power Washing and Roof Cleaning Forum

Dave · Approved Exterior Cleaner

Rust help

Patrick G · Approved Exterior Cleaner

I don't know, but how about a test spot on the bottom one seventh in from the left?

Fred W · Guru

I think a test spot is always the way to go! I've never cleaned such a large area with F9 but I have had to "feather" it out a bit (don't feel that would be worth it for this type of job).

F9 can leave a clean streak if the rust stains spread out and you don't get all of it.

Dave · Approved Exterior Cleaner

We will be doing a test spot before we commit to the rust removal. Regardless if the rust comes off, we will be washing the building to remove the mold

SprayWash · Approved Exterior Cleaner

Those spots are likely caused by Iron Ore that is in the block. I've had varying degrees of success at removing them. Like one spot disappears like magic, then another spot tow feet away doesn't budge. Set expectations. Don't apply F9 ( or anything) too liberally, or you'll be dealing with light spots. I've even tried applying it with a soaked rag soaked to avoid overspray.