Rusting window sill

[princeperch]

<a href="https://ibb.co/vP35P9t"><img src="https://i.ibb.co/yy6Ty23/IMG-20200328-WA0009.jpg" alt="IMG-20200328-WA0009" border="0"></a>

Not the best picture I appreciate. But on my fairly standard terraced house one window sill has a few rust patches on it.

The bay window below and the other first floor window have no patches. So I'm slightly confused why that is- there is no leak from above that I can see that might be dropping rusty water on it.

I've tried to treat the patches with a rust killer, might work might not, but there is one very stubborn rust patch which doesn't seem to have changed colour.

So before I stain stop and paint with masonry paint- would it be overkill to get my angle grinder out and grind out the rusty bits and then fill and paint ?

Any pointers appreciated

[princeperch]

Maybe this will work

https://ibb.co/GvYqtR0

[bimsb6]

Thats an odd colour for rust.

[princeperch]

The green tinge is the anti rust treatment I put on yesterday (it's meant to dissolve the rust I think as it's acid based). Doesn't seem to have done anything

I'm inclined to grind it out, treat again with the rust eater, then fill and paint. I just cannot work out why it's rusted. Its stone ?

[LimSlip]

You sure its stone and not precast concrete?

[princeperch]

Limslip no I'm not 100pc certain. If it were concrete would it have a metal angle bead along the edge which might be causing the rust?

[LimSlip]

It may have some kind of steel reinforcement if it's concrete, it's the only thing I can think of that could be rusting.

[princeperch]

Not sure if I'll makes a dog's dinner of grinding out the edge that's showing rust, or how far through the rust has gone. It's gotta be worth a try though as it's pretty unsightly at the moment.