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ups.com...
Is there any reason why I wouldn't want to use either 1/4-inch lauan
or hardboard as underlayment for 3/4-inch oak flooring strips
(nailed)? The subfloor is 3/4-inch OSB with somewhat rough, uneven
surface and hardened glue in some places, which is why I want to put
down an underlayment to provide a more even surface for the finish
floor. I know I could use 1/4-inch plywood, but that is a little more
expensive than both the lauan and the hardboard. But if there's a good
reason not to use one or both then I will spend the extra money for
the plywood to ensure a solid installation. Also, what is the
recommended way of attaching 1/4-inch underlayment to the OSB
subfloor? I think the 7/8-inch staples I already have would be the
quickest - is that okay? Thanks!


Save your money. 1/4" anything will not add any appreciable strength to the
floor unless you glued and screwed it in place to achieve a complete bond
across the entire surface. Staples would be the worst fastener to use,
followed closely by overdriven gun nails. The plywood will span lumps worse
than 3/4" flooring strips. Your chances of floor squeaks will increase
significantly. And the normal staples used to install the strip flooring
will perform worse through the 1/4" material.
Get out a hammer and wide chisel and knock off the glue and any other glop
on the floor. Drive down any proud nail heads. Chisel down any swelled
joints. Use a thick underlayment paper like heavy felt. And run the flooring
perpendicular to the floor joists regardless of any aesthetic
considerations.
The hardwood floor manufacturers association has never recommended
installing hardwood strip floor over OSB plywood due to poor fastener grip.
The engineered products like Adventec are approved, but not true OSB
plywood. But this defect could be overcome by using extra fasteners.