Q:

How do I remove a small amount of water based concrete sealer from a painted floor?

I was using a water based concrete sealer on my painted concrete floors. I did something wrong, and one tiny section didn't dry clear. 
My question is, what can I use to remove a small portion without removing the underlying latex paint, so I can give it another shot? I'm assuming since it's water based it wouldn't be too challenging to use some kind of solvent, but I don't want to make things worse.

A:

This is a film sealer, as opposed to a penetrating sealer (bare concrete, grout).  I know of no solvent/stripper that will remove an acrylic finish that won't remove (or damage) a latex undercoat.
I would try a reverse progression of grits, until you get to the paint.  You may need to wait weeks for a hard enough/dry enough sealer surface.  Start at 600 over a sanding block.  Only go rougher if you make no progress (320, 220, 120).  Only sand enough to get TO the paint, then recoat with the sealer.  If you have access to a sprayer, it will make blending the areas easier (to hide lap marks)

