| HELP "flattening" subfloor for laminate install
Greetings and thanks in advance for all help!!!
I am rehabbing our kitchen, cabinets have arrived, and I need to level, more accurately "flatten" the sub-floor. Our home is 125 years old, the current kitchen floor is 6" wide oak tongue and groove planks, with no subfloor, so theoak T&G is the subfloor. It was a 15' span and I originally was considering tile so I installed a beam in the basement to halve the span, and I screwed the planks down, every 16" at each floor joist. Since that time we have switched to laminate "hardwood", i.e. a floating floor. So currently the "subfloor" is tight and stiff. Although I tried to lift the sagging joists as much as possible when installing the beam, there is still a maximum 1/2" valley in places. After leveling I was planning to screw down 1/4" plywood to provide a uniform surface.
So the question is how to flatten this prior to installation? I was recommended to use planipatch and screed fill the valleys. I called the manufacturer and they recommended against because the product isn't recommended for plank flooring, only plywood. He was concerned about mechanical movement of the planks with heat and moisture contraction and expansion. I'm sure I didn't eliminate it, but I did tighten the floor a lot. Sometimes it's hard to tell whether manufacturers are being ultra conservative? So I am still tempted to use some type of patching leveler...
Others have told me to layer tar paper but 1/2" seems like a lot of tar paper? Others have said plywood scraps. I wanted to avoid self leveling compounds because the old planks have a lot of gaps from shrinkage over the years and the material will seep into the basement, plus I really only want to fill the valleys, not raise the whole floor.
I have also installed hydronic radiant under this subfloor (in the joist bays underneath). I would prefer to say away from anything that will limit heat conductivity.
Maybe I am taking a risk and maybe I'm crazy, but it seems a pour and screed approach is the easiest, but this is my first floor and I am needing advice from someone more experienced than I.
again, thanks!!!  | 
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