Filling Travertine Tiles

go to a marble supplies wholesaler (someone like http://www.crawshaws.co.uk)

They will have two pack resins available in a variety of colours used for stone countertop fitting, these should do the job.

Basically this is a sign that the factory are using a low spec cement based filler rather than a resin type, production costs are cheaper but you've found out why. Buy a reasonable size tin of this stuff you'll need it again.