How to clean dried in grout off non slip tiles

You can get an abrasive tile sponge specific for removing grout from most builders merchants.

Try vinegar and a naill brush. if you haven't the stomach for it. Then brick cleaner {acid} will do it but avoid the grout joints. Use gloves and slosh water over it first. Soak up the excess with a sponge. That'll do it but if they are porous tiles youll find the haze is deep down in the tile and probably won't get rid. Some tiles must be sealed before grouting.

Scotchbrite pads and handle from Topps tiles- they have different abrasions for stubborn stains. Bob

For grout left on a tile use an emulsifying pad, you can get them at any Decorators Store. It is an abrasive pad that you simply rub over the tile and it polishes off the grout without affecting the tile. If the grout is particularly stubborn, dampen the pad as it softens the grout. All done