Flooring Tile - Grout over grout?

We bought a house with a large tiled kitchen, hall and laundry area. The tile was placed about 8 years ago, and is in good shape, other than a couple that are broken and I am replacing. Unfortunately the grout is a real problem. With grout spaces over a half inch wide, I'm assuming they used a sanded grout, but it is not only very discolored in all traffic areas, it is really scooped out between the tiles. The grout seems to have been placed like this for some reason. Its not dry or cracked, its just not at all level with the tiles, which traps dirt that cannot be swept out, and means we have to vacuum all the time.

Can I just add more grout to these areas and if so what preparation needs to be done to the existing grout, as far as cleaning, etching, etc. Do I need to use the same kind of grout, or can I do as a local handyman suggests and use a new premixed stainproof grout available in local stores? This product's main ingredient is Acrylic-Styrene Copolymer, and the manufacturer claims that "unlike traditional grout, it will adhere to old grout and appear as new". It is guaranteed for 25 years, and the only instructions are to remove enough old grout so that it is at least 1/8 inch below the surface of the tile, which ours already is.

I'd be grateful to hear from anyone who has grouted over old grout, and also anyone who has used this new type of premixed grout. Obviously I'm trying to end up with a durable long lasting grout, with minimal effort!

Thanks!

First, forget that pre-mixed stuff or any brand of pre-mixed, it's all garbage. :thumbdn:


You need to remove at least 2/3rds of what is there and re-grout with cementbased grout you mix, if you can live with what you have but want to clean it up, use a grout colorant.:)

Thanks very much Tileman. I'll do it right. Dang!