I put down some engineered on a slab floating about 5 years ago. They
do have a hallow sound and heels,etc are loud. pergo type stuff is
pretty thin, i used 1/2 enginereed as opposed to thinner planks. I
would have preferred to glue, but my main concern was in florida
humidity and the glue eventually coming up since the house gets hot in
the summer when we've got the house open using the pool, then cool at
night when we close up and turn on the ac.