We're having a composite deck (Timbertech Twinfinish planks - not the tongue-and-groove product) installed, and our contractor is affixing the planks to the pressure-treated framing by using a combination of heavy-duty polyurethane construction adhesive and galvanized nails.

This is not the standard procedure recommended by TT (which is stainless screws or composite deck screws) but our contractor assures that he has successfully done this in the past. The reason he does it is to avoid seeing the screw heads. He says that using screws is "overkill" to keep the boards down.

When I asked whether the glue would make it difficult to replace boards in the future should they need replacement, he said that it would be no more difficult than if he used screws and a screw head popped off, which he says happens frequently. He said that the glue could be scraped off without taking the framing with it.

When I asked whether the glue would prevent the boards from expansion/contraction, said that composite boards don't really move.

Questions: (1) Has anyone else used (or heard of) using nails and glue instead of screws for composite decking? (2) Should we be concerned about the longevity of the construction, expansion/contraction of the decking, difficulty of replacing boards, or anything else?

I am just a layperson and would really appreciate some expert advice.