This is a very interesting situation we have found. I'd like to give a little history and I have a photo below but have more if needed.  Hoping you all might help me solve this mystery.

Old farm house was restored and had a large addition built onto it about a year ago.  Client had not yet moved into the home. (No furniture, no people) Another contractor installed Creme Marfil all over the house (showers, floors and tub surrounds). The stone is from Spain and the manufacturer is MSInternational. Un-sanded grout was used for the installation. 

The General Contractor who built the addition has been working with us to try to determine the issues and was able to give us lots of information. 1) The original sub-flooring was left in place in the areas that were original to the home, 2) the original vinyl floor was left in place, 3) an additional plywood wood substrate was added on top of the vinyl, and 4) Ditra was used on top of that 2nd substrate layer prior to the tile installation.  During our inspection, we found areas of rotted wood from the original layer of plywood that was just covered and had an odor.

The issue we were called for was because the marble has swirl marks and was etched and hazey.  We found that the previous contractor/original installer had used a grout haze remover to clean the grout haze (acid based) etching the surface. Then, in an attempt to correct this issue, they crystallized it and used a 0 or 00 steel wool pad badly scratching the surface, locking in the scratches and etch marks and making a big mess. (We also have before and after photos, along with photos supplied from the GC of the original installation process).  Other issues included loose, chipped, broken and un-matching tiles which we replaced.

We diamond honed, removed all the crystallizers (the slurry was originally black and awful and it went clear as we completed each step)...I hate crystallizers.  

During the process, we had to leave the project for a few days to accommodate another client and as we waited for the manufacturer to send us more tiles (took a while to match the dye lot).  While the house stayed empty for those days there was a storm and oddly there was a lot of dust all over the house.  It was cleaned and we continued with the restoration process.

We did the typical multi-step restoration process, cleaned it with a ph neutral cleaner and sealed it with a water-based impregnating sealer.  All looked amazing our client said. We detailed every nook and cranny and even did a lot of hands and knees to get all the details. Took us a little longer but it was worth it because it came out beautiful and the client was very thrilled.

About a month has passed and suddenly this strange powder has appeared (it looks like it is coming from under the walls) all around the surfaces.  The floors around the 1/4" shoe molding have it coming and from under the toilet.  I have never seen anything like this.  

The customer's GC says he thinks it is the crystallizer or our cleaner.  But this just seems impossible to me.  Crystallizer wouldn't powder up like this and ph neutral cleaners wouldn't either.  We did use honing/polishing powders but none are this color or have the odor this residue has.

I am thinking possible bug issue or an issue with the seal of the house allowing dirt in.  But it is a fine powder like substance that just sits on top of the surface that has an odor. In some areas it is lighter than others. In the heavier areas it is like a light layer of pollen or powder snow like you can make markings with it with your finger. It is not sticky or even leaving a residue when moving it with the finger.  Like a dry smelly dust.  This is what makes me think bugs because of that old substrate.

Any thoughts?

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