The master shower Mapei grout has failed and been replaced 3 times in 2 years. Some sections tend to dry weak and 'crumbly' and can be removed w/ a fingernail. But all the pewter Mapei grout that gets wet (it is a shower) turns to 'mud' and eventually 'washes out' over time...

The same Mapei products in the other showers (DIFFERENT COLORS!) and kitchen backsplash is rock hard and works great. The tile flooring that covers 100% of the rest of the house (may be Polyblend Plus Sanded) - equally great. It's limited to the Mapei pewter in the master shower.

Based upon what you've shared above in your post, I would be wondering what is causing the issue with the grout = there is an issue with the construction/waterproofing of the shower (or maybe there is a humidity issue in the bathroom that isn't being addressed by your bathroom fan).

Why would one particular color of Mapei Ultracolor Plus FA grout have an issue - while all the other colors that have been used in your home have been fine? That makes no sense to me.

Unless you used a different tile pro for that one shower and he/she doesn't know how to mix/work with Mapei Ultracolor Plus FA grout. That's the grout my tile pro used in my showers (not pewter - but again, why would the color make a difference?). If the same person has worked on your other showers that have had no isssues, then it isn't "user error."

Have you contacted Mapei?

Mapei would be very interested in a product failure like this. Who mixed it, and with what? There's a very specific mixing process to FA that needs to be followed.

I'm not explicitly blaming pewter - just stating the results. Two different pros did the first 2 installs. First one did the entire house originally - few thousand SF of tile and it was outstanding everwhere else. They mixed w/ machines. 2nd one was redone under warranty by owner of 1st company - also new bag and machine mixed. It lasted a little longer but probably because by now I was treating it super delicate to extend life. I did the 3rd one (now out of warranty, I'm just an amateur) and I mixed by hand w/ yet another new bag following the rather simplistic Mapei instructions (found on bag and online). I made multiple batches to use on test boards as well as a few select spots in the actual shower. I also experimented w/ slight sloppy and slightly dry mixes and slaked. All my results on multiple test boards using both a new bag (and for kicks the old bags) faithfully reproduced the crumbly mud dauber results.

As an additional control experiment to validate mixing techniques I also tried a few test spots on old boards with some 2 year old original opened Mapei bags in OTHER COLORS used elsewhere in the house. Using same hand mixing technique as above. These old stale bags produced excellent results - very hard, could not be removed w/ a fingernail, and did not turn to mud when moistened later.

Other than getting a refund on the last bag I purchased - At this point I've wasted too much time on the Mapei pewter rubbish. I'm just looking for a comparable NON-Mapei product to use in a shower grout and I'll live w/ a mis-match color if necessary.

QUESTION: Polyblend is readily available to me - any particular product line there someone might recommend I consider with some color choices to find something similar to pewter gray?

Thanks,

Polyblend is garbage standard grout. FA is the premium grout of choice among many many professionals. (Just read the Tile the World FB group) Just because you got an expired or defective bag from a source doesn't invalidate the high quality of that material. That's why you call MAPEI. It's a high quality product that any manufacturer would stand behind. 1-800-992-6273

Polyblend Plus Sanded Grout can be used for joints between 1/8" and 1/2". #543 Driftwood and #165 Delorean Gray appear closest to Mapei #5002 Pewter on my monitor. You can pick up color grout sample sticks at Home Depot.