I am not in favor of topical sealers especially in showers; but many of the local tile setters here in Kansas just use the Tile Lab product. Its water based and low voc. a more toxic sealer is Sparks Stone Glamour. personally I would suggest just using some 5x and sealing with a good impregnator sealer

From: Barry Raduta <barry@diamondstoneandtilecare.com>
To: Stone and Tile PROS Technical Support <sccpartners@stoneandtilepros.com>
Sent: Wednesday, September 25, 2013 6:57 AM
Subject: [sccpartners] Topical sealer

Hi Partners,
I am looking at a vertical Travertine shower wall that has that "old world" look with many holes and a honed/ satin finish (not really shiny).  It looks like the majority of travertine that is out of the box.  The house has travertine floors (different tile than the shower vertical walls) everywhere and the finish very shiny and I even saw unused floor tiles and they had a coating on them that actually looked like "liquid plastic" . 
My question is, does anyone know of a topical sealer that I can use on a vertical travertine shower wall that would be easy to use and have a shiny appearance?  Of course, I would thoroughly clean the walls prior to applying the sealer. 

Thanks,
Barry

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Thank You,
Barry V Raduta
Diamond Stone & Tile Care-South
Stone & Tile Pros
843-540-1445