ᐅ Rust stains and marks on concrete slab

Dear Forum,

We planned to leave the raw, unplastered concrete ceiling in our new build exposed. However, for cost reasons, we did not order architectural concrete. We still really like the concrete’s appearance, but there are impressions from rubber pads that the ceiling rested on, as well as some external rust stains caused by contact with the reinforcement.

Now the question is whether these can be removed at all, and if so, what is the least labor-intensive way to do so.

First, I want to try removing the stains chemically. There seem to be good products available. However, working overhead with ascorbic acid is very challenging. I’m not sure if this will be successful.

Our site manager suggests sanding the entire ceiling surface. However, I am unsure whether this is a promising approach and whether it might dull the concrete or leave visible sanding marks later. Is it possible to sand only the affected areas?

The last option would be to apply filler to the ceiling and then paint it. But I would only want to do this as a last resort. Does anyone have experience with this?

Yes, you get what you pay for…
That looks superficial. I would also sand it.
With sanding, you can make concrete mirror-smooth if needed… so the opposite of dull.
How are you planning to handle the wall junctions and joints?

I can’t help you directly since we haven’t started building yet, but we are also considering an exposed concrete ceiling. If you find a method that works for you, please feel free to share the results here. I’m especially interested in how a polished concrete ceiling looks. The appearance can ultimately be influenced by the grit used. We plan to fill the joints with mortar and seal the edges with acrylic. The walls will be white.

How polished concrete looks depends on the concrete itself and the grinding process.