@hu-867564120 seriously, I actually emailed the grout company to ask what we can do to fix this and am waiting to hear back!

Solutions:

- Remove grout and replace. Huge PIA.

- Dye the grout.

- Sell and move out.

I had a similar problem. I think in my case what caused it it was that my new tiles where covered with something ( of course I didn't know about it at that time. That is how they arrived from the store). The tiles had shadowy variations and when I went and open the new box of left tiles and moved my hand across the tile some powder??? was left on my hand. It wasn't really that visible on new tiles unless you moved your hand over tile. I think after grout was applied and later wiped off the tile with sponge this dirt from the tile was transfered from tile to grout lines. It was only in some places, mostly where tiles had darker shades.

Don't blame the grout. It is packaged with specific application instructions.

@J Sk That's crazy! you would think manufactures would foresee this kind of thing before putting the product out on the market. Very possibly the same thing happened here, I have no idea... and apparently neither does my contractor hahaha. Wish I new how to correct and @HU-867564120 unfortunately moving and selling the place is not an option since we just got it, we don't want to dye it since who knows, that might make it worse!! and I don't think our contract thinks its a big enough issue to "fix" :-/

Powder, wax etc. are normal in the manufacturing and packaging process. Manufacturers do foresee this. That is why EVERY grout package will state "All surfaces must be clean and free of any debris". Which is common sense anyway.

Stop blaming the products for installer errors. Did you contact Bostik? Send them photos? If you want a factual answer reach out to them.

@Creative Tile Eastern CT No one is "blaming the product" hence the question " Does anyone know why this is happening?" ( blaming would be saying: "this product is bad because a,b,c which is not the case as you can see from all the above posts). It seems like no one can give us a straight answer as to why this would happen all over the bathroom in random spots with 2 different grout colors. .... And yes I did reach out to the company (as you can see in one of my comments above 3 days ago), Haven't heard back yet but will keep you guys posted.

Sorry. Missed the emailed company comment.

Why. Installer failed to follow proper mixing / application procedures. Seen this exact scenario many times over the years. Often the color is washed out due to excessive water in the clean up coupled with inadequate drying time between steps.

If your installer thought it was a product issue he/she would be calling Bostik. Simple as that.

Solution - Regrout correctly.