On Sat, 23 Feb 2013 06:20:02 +0000 (UTC), "Danny D."
wrote:

The MSDS for Lime Away says it's 2.5 to 10% Sulfamic Acid (CAS 5329-14-6).
http://www.rbnainfo.com/MSDS/US/LIME...US-English.pdf

I have never heard of Sulfamic Acid but Wikipedia says it's used to
remove rust and lime by converting them to soluble calcium and iron salts.
http://en.wikipedia.org/wiki/Sulfamic_acid

I'm guessing that the phosphoric acid mixes with the lime to create a
salt which is then washed away by dissolving in water.

I've used Sulfamic tile and grout cleaner. I see now they sell spray
bottles of it.

I used this one.

TileLab Sulfamic Acid Cleaner

SULFAMIC 1 lb pkg

Concentrated crystals that mix with water to make a safe to use, acid
cleaner. Removes cement grout haze, mortar residue and efflorescence
Use on tile or colored grouts . No toxic fumes.

http://www.amestile.com/upload/accessories/Sealers%20and%20cleaners/sulfamic.jpg

HD sold last time I checked.