New marble mosaic on wall is very patchy and dirtier than before it went up

[enduro]

where is it available, is it expensive.

Go to www.drytreat.com they will tell you local stockist and prices. Drytreat make very good sealers but they are not cheap.

 

[Rich]

Do you know if the tiler sealed the mosaics before he grouted/after he grouted or both?

If the haze comes off with elbow grease and water then it should be fixable but IMO this should be done by the tiler.