Grout or sealant?

[maf20]

Evening!

In the process of laying a natural stone patio, butted up against a railway sleeper retaining wall. As wood shrinks and expands, should I use a flexible sealant between the stone and the sleepers or just a usual grout as with the rest of the patio? Would the usual grout crack with the movement of the wood?

Cheers

 

[Thermo]

we normally point it as normal, or put a cover bead over the gap. Shrinkage is fairly minimal