We are getting ready to install 700sf of 7/8 x 4 antique heart pine on plywood on the second floor of a residence. The owner wants us to use a sound deadening underlayment.

Do any of you have a favorite underlayment for this purpose? Will the staples from our M111fs transfer sound through the underlayment?

I first thought of cork but would like to know if anyone has a better plan.

I use FloorMuffler underlayment under floating floors and it is supposed to be a good sound deadener for nail downs.
http://www.flooringunderlayments.com/floormuffler.html

Jerry, I did not find any info on installing Floor Muffler under a nail down floor but this is probably just what we need so I will call them tomorrow to make sure it is approved for this installation and try to find a distributor in our area.

Thanks