what im talking about is when you use it to clean stains off of an inground pool that has sat for a period of time and has stains


http://wiki.answers.com/Q/How_do_you_us ... h_concrete


and as you can see from the last few lines of answer #2 "Handling Concentrated Acids"

also read the first few lines of the answer #1 "Etching Concrete"

Not to get too far off topic about cleaning your pools but if you have a machine shop that you use and like and happen to be friendly with the owners then that is pretty much the best method that I know of. The guys I know generally have an engine cleaning day that consists of a caustic soda bath followed by hot pressure washing. If you ask nicely they may dunk it for free with an engine, or you can offer to do the messy pressure washing for them. This obviously isn't available to everyone but neither is bead blasting. Even if it costs a few bucks it's better than pouring chemicals (diluted or not) down my driveway.

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I second (or third) the vote for oven cleaner. It works very well on grease,oil,and carbon. Use rags to wipe it off. Dispose of the dirty rags the same way you do after an oil change. Oven cleaner works better than the "foamy" engine shampoo. I bought mine at Wal-Mart,but perhaps the "Dollar Stores" have a less costly generic version?