What causes quarter sized rust spots on driveways?

[The motor guy]

I always assumed it was the steel rebar in the concrete rusting and coming up to the surface, am I wrong? What are other possibilities. I did some pressure washing for a customer and he thinks I missed spots, when really you can't remove rust by pressure washing.

 

[andyd]

It is common, just a chunk of something ferrous in the aggregate.

 

[The motor guy]

They're on [censored] near every driveway I see. Maybe fertilizer spilled?

 

[The motor guy]

Originally Posted By: andyd
It is common, just a chunk of something ferrous in the aggregate.


So it technically is just the rebar rusting? That's the only steel I know of oh and I guess they have steel ties that tie them together too. I haven't really looked at how a concrete is structured lately.

 

[L_Sludger]

As a lad, I found out that owning a car with an oil leak accords you the benefits of rust-proofing every driveway you park on. Most of homeowners don't see it in such a charitable light, however!

 

[JHZR2]

Ive never noticed them, except when applying iron fertilizer.

 

[tom slick]

I'd bet on fertilizer stains. It would be a really bad concrete job if the rebar was causing spots and would probably have some spalling.

 

[HoosierJeeper]

http://www.autogeek.net/carpro-iron-x-cl...channelid=BIZRA

Could try this stuff. Heard it's worked on concrete to get rust stains out. You can get a smaller size, I just found that one first. Sonnax makes one called "Fallout Remover". Smells way better. But both work fine.

 

[BigD1]

Premium fertilizers contain iron, so yes it's a good bet that's what's causing it.

 

[Blueskies123]

I always use my gas powered blower around the edges of all my drive ways and walk ways after spreading fertilizer.

 

[totegoat]

Some oak leaves stain concrete.