We are refinishing 50 year old hardwood floors. The old varnish was just flaking off. How many layers of polyurethane will it take to create a durable finish. Our 70 lb dog will be walking on these. Also does it matter how thick or thin the layers are?

I have rehabbed five houses, none of which had hardwood floors. I just purchased a house with hardwood floors that need to be refinished. I am handy but not that handy. Should I rent the equipment and go for it, or should I contract out.

I have applied the 1st coat of polyurethane, let it dry and have now sanded it. After removing the dust w/ a vacuum, should I use a tack cloth to wipe it down and remove any remnants of dust and dirt? Because the tack cloth seems to be soaked in a liquid petroleum base of some sort, I am wondering if the chemical in the cloth will have adverse affects when combined with the final coat of polyurethane.