The only thing that has worked so far has been a steel brush. I have not seen any damage on the porcelain using the steel brush but I am worried I will scratch the porcelain. I have read about using wood dowels to remove grout from pits on porcelain which makes a steel brush seem extremely harsh to use on the porcelain.
Can I continue to use the steel brush or should I try Sulfamic acid?
I purchased some Sulfamic acid at Home Depot and the directions said let the cement cure for 10 days. I left the Sulfamic acid container at my mother's house and I don't remember if the word was "cement" or "grout." I worried about using the Sulfamic acid and its affect on the grout lines I want to keep while I was removing the grout from the porcelain pits.
How long should I wait to apply the Sulfamic acid?
How much should I dilute the acid at first and can I use a stronger mixture if my initial efforts still do not work? How much stronger?
What type of brush/sponge/pad/etc should I use with Sulfamic acid?
I have previously read when using any acid, have ventilation and eye protection, and rubber gloves if you have sensitive skin.
Any recommendations or suggestions are appreciated. Terry