I need to clean the grout on our kitchen and bathroom floors. I got some great direction and ideas for our wood floors so...what do you suggest for a rough stone tile floor?

I am editing to add that I'd really like to find non commercial/low chemical solutions to try.

(From Cmouse, who's dh runs a tile cleaning/restoration company):

*** n Span or Mr Clean.  Anything that is alkaline (non-acidic). Do NOT use vinegar (acidic) or bleach (caustic) as both will eventually damage your grout.

Ugh. Grout. I was able to get our bathroom grout sparkling clean but this was wall tile, not floor tile. And I did use bleach, which I know is something you don't really like to use. But I found a tiny bit of bleach goes a long way.

In an old plastic margarine container I mixed a couple tablespoons of bleach and enough baking soda to form a paste. I used more baking soda than bleach, maybe 1/2 a cup? Using an old toothbrush, I applied the mixture on my grout and gently scrubbed. I let it sit 5 or so minutes and then used a rag and warm water to wipe it all off. My grout was so clean!

But this recipe does use bleach and it may be too harsh for what you are looking for. But it was very frugal!

I used X-14, sprayed, closed the door for 10 minutes, went back and clean.  This was bathroom wall tile, though, and some mildew was apparent (no exhaust fan).

 I use a vapor steamer. 

 The initial cost is more than a bottle of cleaning liquid (mine was $150 and home units go up to in the 3-4 thousand range) but I use the machine on everything -- even humidity in the winter.  I heat the machine, spray on the lines, use a bbq brush on hard stains, then wipe with a towel.  Actually most of the time I don't do it.  The kids love it.  If they want to buy a dvd or game, that is how they get it.  In our house it is a win-win.

 I find that using a steam cleaner gets my grout very clean. It lasts for six months and is non-toxic. 

 Before you go out and buy something, try half dish soap and half water with a toothbrush or small scrub brush. We used that on wall tile when I worked in motels and it did a great job. I don't know how well it will work on floor grout, but it would be cheap to try. 

great idea!  My mom got one of those steamers from sally ann in the box.  She wanted one for a long time and found it at her price cheap!  I have to borrow it and do our floor grout in the bathroom and kitchen.  though me and steam are not a good mix.

 The dish soap did not get the grout entirely to the original color but it looks much better and it was very cheap and less toxic than commercial grout cleaner. 

For others who have grout to clean, The Dollar Stretcher has an article up on it. 

Another bleach-based idea that I found very effective. It is NOT Earth-friendly, however.

Wearing rubber gloves (oh boy, you can already tell this is going to be bad), dip a few paper towels in a mild bleach/water solution. Hang these against the wall where the gross grout is (for wall grout, obviously). Leave it. Come back in an hour or longer and the grout is gorgeous. All you have to do is spray off the disintergrated paper towel.

 I like this better than using spray stuff which I feel like gets everywhere. This way I have much more control over the area.

 Has anyone tried the vinegar/baking soda solution? If that works well, I'd probably prefer that. I'm trying to wean myself from bleach.