Did you use spacers?

At first when I looked without reading, I did not see anything wrong; now that you pointed out the issue,I see the slope. I'm not sure that a not "flatter" surface is the issue that caused the slope????

Wall flatness wouldn't cause a downward slope. Are your cabinets level?

It's easier to clean those joints when the thinset is wet than chipping it out before grouting. Raised areas will show white. The gray thinset would also hide better. I think it needs to be cleaned out 2/3 the way down into the joint.

How are you ensuring even spacing between tiles?

I did use spacers (1/8"), but I had trouble in some areas which I think may have been part of the problem. The spacers are shaped like a cross, but our natural stone tiles are of varying thickness. I noticed while I was placing the tiles that the spacers wouldn't insert all the way when an especially thick tile was adjacent to a thin one.

With material like this, you need to "cheat" your spacing to keep things level. I would remove about two tiles at least halfway down and re install them using spacers, wedges, folded cardboard or whatever it takes. Be creative....use gray morter this time and grout it with a dark gray, sanded grout.

What StoneTech says. Use a level to keep your row level if you can, then "cheat" as needed : )

I'm curious stonetech, why do you suggest sanded grout for a backsplash? Not objecting just want to learn : ))

If a picture or mirror is a 16th of an inch off level, I have to straighten it or it drives me nuts! Imagine my distress when I discovered that the wall posters in my doctor's office are screwed or glued - crooked - to the wall. I would have to start over if that were my kitchen.

gr8day, the standard use of sanded grout is to use it with 1/8" space or greater. The shrinkage with unsanded is such that the gout will crack, I believe. The sand in the grout adds structural strength so is can't shrink so much. Am I right StoneTech :) ?

Bumping up....

I vote with the wife and father. You're almost to the end anyway. It's a backsplash; you'll probably have something in front of it anyway.

Finish it and live with it for a while. If it still drives you nuts in a few months, tear it out and do it over. That won't be much more work than adjusting this now.

Remember, caulk, not grout, between the top and first row of tile and at plane changes.

Enduring....Yep, you're right! Sanded is stronger and doesn't shrink as much. Last one I did in Houston, I used "Fusion Pro" grout. Very fine sand and he loved it!

I might add, although it's a bit late...when doing a backsplash, ALWAYS space the bottom row an eighth of an inch off the countertop and caulk that with a matching, sanded, silicone caulk as microscopic movement WILL cause it to crack if you grout it.

Thanks! I was curious about the sanded grout, when to use and when not. Thank you both again for taking the time to post the information.

I had no idea that sanded grout was stronger. Thanks for sharing.