Problem with grout colour over previous grouting session

[Neil23]

Hi there.

I'm using TEC AccuColor premium sanded grout on my bathroom floor. The colour is "light pewter" which is a fairly dark gray colour and an excellent match to the tile.

Two weeks ago I grouted roughly 80% of the bathroom and was very happy with the result. The colour was very consistent and dried to a color that was very similar to the color sample.

Yesterday I finished the job, but hit a snag in the process. I'm hoping you can offer some advice.

At the start of the process two weeks ago I mixed the dry grout to ensure the pigments were evenly distributed throughout the batch, so I don't think that's the source of my problem.

Having read that the ratio of water to grout can influence the colour, I've been extremely careful when mixing batches of grout. I'm sure the veterans out there will get a good laugh at this, but I use a digital kitchen scale and measure both the water and grout powder to within 1 gram. I've been mixing 1000 grams of grout into 165 grams of water. Some people say I'm anal, but I prefer the label precise ;-) My process for mixing the grout (technique, timing, slaking, ...) was exactly the same as well. I don't suspect this is the source of my problem either.

Yesterday I packed the grout with the float as I had previously, then let it set up for roughly the same amount of time as I had previously. Things seemed to be going well. When I contoured the grout with my sponge, however, I got a light gray film on top of the adjacent grout that I had installed two weeks ago. I tried wiping it off with a damp sponge, but no luck. Looking at it this morning I have darker grout lines where the grout was installed two weeks ago and untouched yesterday, darker grout lines where I installed the grout yesterday, and light grout lines where the grout was installed two weeks ago but where "new" wiped-off grout came into contact as I was contouring the grout yesterday.

I'm really disappointed in the final appearance of uniformly dark grout lines with more or less just a single light grout line in the middle in a really obvious place on the floor.

Any suggestions on how I can remove the light gray layer on top of the previously installed (and dark) grout?

Thanks so much in advance for your help with this.

Neil

[bbcamp]

Neil, it may be that there was excess water in the sponge and you transferred a bit of new grout onto the older grout. If that's the case, it should come off with a good scrubbing with vinegar and water.

[Neil23]

Thanks for the response Bob.

I mixed up a solution of 50% white vinegar and 50% distilled water. After letting it sit on the lighter grout sections for a few minutes (probably 3-5) I scrubbed it thoroughly with either a green nylon scouring pad, or a stiff nylon brush (I tried each on a different section). I used a shop vac to remove the solution, then rinsed with water and removed that with the shop vac. Not only did the lighter sections not darken up, but the adjacent portions of grout (that started out darker) that came into contact with the solution in the course of the scrubbing are now the lighter gray colour as well ;-(

Now I have a larger section that is the unwanted lighter colour - argh!

Can anyone suggest what my next move should be?

Thanks.

Neil

[Neil23]

Any ideas?

Thanks.

Neil