I recently had buckling in my old parquet floor. The parquet was glued down to a concrete slab. We are on the 6th floor of an apt building in the Northeast. I also would like to reduce some some noise for my neighbors downstairs. The parquet has been removed and there is a bunch of remaining old black glue leftover. My contractor gave me 2 options. He said I could glue plywood down to the concrete slab and glue or nail the engineered wood to that. Or I could put plywood down, an underlayment, then float the engineered wood. Is one option better than the other in general? Is one better for noise reduction? Thanks in advance for any responses.
Prior to settling on a floating floor... Have you ever walked on a floating floor? I have and they have a sort of sponge feel to them underfoot and there is often a hollow sound as your foot (with shoes) hits the floor. I do not know if this is because it is not attached to the floor or if it is just the nature of the boards. But, I can spot a floating floor in two foot steps and I think they are all kind of weird to walk upon. My personal opinion only. Therefore, I would go with the underlayment and the cork sound barrier and nail or glue the floor down.
You can purchase a levelling compound at most of the stores like Home Depot, or Lowe's. It's a little expensive, but compared to the work involved with removing the lino adhesive the cost usually seems worth it. Levelling compound comes in a can, and is spread over any rough floor surface with a smooth edged trowel, and after it dries your floor should have a smooth surface. As for your engineered wood flooring, I have never heard of any that is applied by gluing. Most of the ones I have used in the past interlock, and the entire floor system floats over the sub-floor so that it can allow for any expansion or contraction of the different floor surfaces. Furthermore, not all engineered wood floors are designed to install over concrete. But that is not to say that you don't know what you are doing. For every new engineered wood floor system out there, there's a new and different set of rules that go along with it's application. I just thought I would mention it since a freind of the family recently installed some manufactured wood flooring on his basement floor, and when it got damp the material it was made of expended and broke into pieces. The whole thing eventually had to be replaced, and the manufacturer didn't honour the warranty because the floor was not recommended for concrete. Anyway, my answer to your initial question is Levelling Compound.
Floating is probably the easiest and cheapest way to go. Make sure you have a good underlayment because you have two issues: the uneveness of the residual glue and the sound issues from the floating floor. You want the stuff that is more rubbery in appearance rather than the stuff that looks like packing material. There are some design issues to worry about (expansion gaps, carrying through doorways) with a floating floor that a good installer should take care of. Plywood and staples is what I have used in the past. The downside other than expense is that it will raise up the floor a bit and you'll have to deal with the transitions. I've stapled down lots of engineered floors without a problem. Glue is the worst answer. First off the stuff is Nasty (and not exactly cheap, I paid for my flooring stapler with the money I saved on the first flooring job). You must wait a day until it dries before putting the furniture back, etc... With the float or staples, you can just move everything to one side of the room, lay your half floor, move stuff immediately on the side you just put down and finish the rest.
I would opt for a floating floor with a plywood sub-floor and a cork underlay - this will substantially reduce noise transfer to the unit below. I would not glue it down - lots of off gasing and nasty fumes. Nailing or stapling it down is an option but a well installed floating floor will not move up and down or feel spongy when walked on. Also, check with your condominium manager, you may have restrictions on the type of installation you may use in your unit under the condominium by-laws.
