chitowngrl the best "tile" forum inside gardenweb is the bathroom forum. Post there.

Since stone is a natural material, its reaction to this grout cannot be predicted over the internet. Starting with the smallest box of grout, try it out.

Years ago I posted on a tile forum about Freezering most of the mixed grout and using it gradually. I was a pioneer in this. I have found it only works when it works. There are many factors in this equation. Too many to add here now.

It IS possible to split the contents of a box and mix only half a box. This puts you at risk of getting more than half the hardener in one of the two batches, and less than half in the other batch. Measure carefully. If the less-hard batch gets put into the freezer, it will last long. Vice versa, if the more-hard batch goes into the freezer, it will not work well at all. It will harden in the freezer.

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Epoxy grout is good for DIY because they have the time to read instructions and do things right. Professionals experienced in Portland cement type grouts have a hard time with it because it requires them to unlearn some deep habits and to pay attention to "new" aspects of grouting.... so you are best continuing as a DIY.

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Without seeing it, I'll venture a guess my strategy for that wall would be to begin grouting the wall with a Portland cement type grout in the same color. I would not fill the grout lines fully. Then I would go back over it all with the epoxy product you mentioned above. This is because epoxy grout is good on vertical surfaces when it only has to fill shallow gaps.

Epoxy grout is a little bit like molasses. Even when it starts hardening up, it can still slump. My thinking is that epoxy grout can slump, in many of the spaces where you want it not to slump. This does not result in the flat grout surface you want; it can look very unprofessional. Slump means like cake batter or peanut butter sliding down and getting thicker protruding at a point where it's blocked, and obviously also being thinner in other places, which leaves the stone protruding.

I cannot say what to do specifically. I'm not an expert at the highest level. I have used epoxy grout a lot, in many renovation projects. I have used epoxy grout to cover over other grout too. You can confirm that this is possible. Call or email the manufacturer. Somewhere you will read that this grout is good (guaranteed) when it fills shallow spaces like e.g. 1/8th inch. Pre-grouting with old fashioned grout is a fine step to do, it's not overkill, it's something a DIY can do.

Mixing thinset or Portland cement type grout to partially fill the grout lines may sound like a chore, but it isn't when you encourage yourself by reminding your self it's the only way to get the result you want.

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If you want to consider alternatives, read up on "Grout Boost" for Portland cement type grout. It is great for kitchen backsplashes.

Grout is one of the most detailed subjects imaginable. Ignore the comment emknc made.

Thanks Ginny20! I'm new and don't even know how to report someone. I didn't take it personally since whoever it is doesn't know me.

Davidro1, Thanks for posting!

The problem I have with pregrouting with regular grout is what led me to epoxy grout in the first place: I can't use sanded because I don't want to scratch the marble, but some of the spaces are too big for unsanded grout. :( I don't want it to slump though. I will also post this in the bathroom forum and see what people have to say over there.

Thanks!