I had travertine installed on my porch less than 2...

I had travertine installed on my porch less than 2 years ago. The initial job was done well ; that included polymeric sand (which I paid for as an extra). However over the last year, the sealant (polymeric) sand is no longer evident in many places. There are several pavers along the back edge of the screen porch have dislocated from the adjoining pavers (1/4 to 1/2 gap). There was supposed to be drainage as part of install (no evidence of any drain put in) as a result there is a large pool of water that collects; causing excess water to get under the pavers and create separation (some could be due to the fact that the underlying sand was not compacted properly). I called another vendor who investigated and stated that the options to fix can be costly. Either install a drain from end to end; or reseal the area except the tiles will still have a gap/lip (up-down).