@42trainman posted:I think your issue came from not securing the homasote down tight enough. I used 1/2 plywood and 1/2 homasote glued down on top, weighted **** near everywhere on top over night. Mine has been up over 3 years with no issues and flat as a pancake. I think I used liquid nails. I'm guessing you'll need a putty/mud of sorts with a little sanding to get it good and flat. Shouldn't be too bad to work past. Good luck.
Yeah, it sounds like a failure to bond, but I'd be inclined to either rip it apart and reglue properly if feasible, or scrap the existing (and likely warped) homosote and replace with a new sheet. If the homosote has not adhered properly to the plywood, I'd be afraid just patching and filling would leave the layout unstable and uneven, leading to more problems down the road. IOW, I suspect such a large variance indicates there's big gaps between the layers, with warping of the homosote, and that's not a situation onto which I'd want to expend further efforts in landscaping and accessorizing, much less attaching track.
