Some advice please: We're installing 3-7" random width Walnut over a plywood subfloor. The wood supplier recommended just nailing; the installer our general contractor recommends (we met him and seems very experienced) says he almost always glues as well as nails, to prevent too much movement. Any harm in this?? It's a 100 yr-old house, putting down about 1300 sq ft to cover several rooms on first floor.

Anything solid 5" and over, glue it.

Thanks Stephen; you mean glue AND nail...?

Yes, you will get less movement glueing as well as nailing.

Like Howard say's, glue and fasten. You can't do it after the fact! I'm on one now myself.

Especially the 7's . You will stand a better chance of not showing a slight cupping over time.