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I live in a 115 year old house that has existing 3/4 tongue and groove floorboards. While they seem sturdy, they are super ugly and have worn very unevenly, and unfortunately sanding won’t be a solution, due to many nails, knots, etc.

I would like to install new hardwood over it, but I want to make sure everything ends up flat and clean looking. I also have new carpet installed in several rooms and want to keep the flooring somewhat at the same height.

Edit:

I will definitely sand everything to get it flat, but the floor is a lost cause. It was never ‘high-quality’ necessarily. While I don’t doubt I can get it flat, it has some holes drilled in it, patches here and there, and it is not a ‘beautiful’ wood grain, and very plain looking. The tongue and groove are also cut in such a way as to have a noticeable, if very small gap. I’m hoping a thin plywood will add something to the stability, but maybe that’s naive of me.

Assuming I sand everything flat, and use something like liquid nails and 1/4 plywood, will this be sufficient to get a solid, relatively squeak-fee and solid base to attach new nail-down hardwood?

Key detail here is how will this attach best:

What’s the best attachment method for the plywood to existing wood floor? Would screws sit too high (not sink enough in 1/4” ply?) or should I use nails? (Either way I am unsure of size and type) Will the 1/4 plywood be rigid enough?

I also had someone say take out the whole floor and install new 3/4 plywood subfloor, but that honestly sounds time consuming, destructive and like a terrible solution.

What’s my best bet here?

Also, if my original floor is flat after sanding, is the plywood pointless? Should the new floor just attach directly?

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    Pictures will help. Ugly/beautiful is in the eyes of the beholder, but old floor boards are usually in demand. Most of the hard type flooring will want a flat, solid surface. Dips/ridges are not liked, and if enough/large it might be better to start at the beginning than trying to patch/smooth over.
    – crip659
    Jul 3, 2023 at 11:39
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    The floor needs to be flat not level. While having a marble roll from one side of the room to another is annoying, no doubt, if it does so unimpeded, and doesn't jump because of ridges and buckling (small dents in the floor aren't a major issue), it should be fine. If there are minimal gaps under a 6' straight edge in any location/direction, you should be fine. Of course, out of level might mean there are structural issues to be addressed, but that's a whole different topic.
    – FreeMan
    Jul 3, 2023 at 14:22
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    Also, nails can be sunk below the surface and I'm not sure what knots have to do with sanding. If you're hand sanding, yeah, they'll slow you down a bit, but you're already got a 2 year project on your hands (and knees) if you're hand sanding... A flooring sander won't even notice that it passed over a knot.
    – FreeMan
    Jul 3, 2023 at 14:26

2 Answers 2

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I specialize in fixing old houses and I'm currently working on one built 1837. Yes, everybody prefers the old boards, but what most people don't understand is that at some point they will reach the end on their life and must be replaced or covered. Ideally, you should replace them with new boards which are period-correct. But not everybody has the money and time to do that. Hardwood planks is second best. I'm glad you are not suggesting vinyl.

Floors in a house that old will probably be slanted in several directions, with high and low spots everywhere. New flooring will require a perfectly flat, even surface. Otherwise you are wasting your time and materials. There's no way around this.

You can use subfloor adhesive and 1/4 plywood to even the floor, but this will only work for small differences, say 1/4". Otherwise the differences will telegraph. Use a laser to assess how much the floor is leaning. If it's more than 2" from one side to the other, probably a new subfloor is the only way. If it's less than that, you might be able to get away with self-leveler, but it's going to be expensive and messy. Choose your poison.

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I had a wood floor in a house - 90 years old then.

Boards worn like you describe, we used an 18" drum sander, first diagonal with coarse paper then other diagonal with smoother paper. After that a finishing sand parallel to grain.

Came up a treat and once treated was a beautiful floor.

Takes a lot of time and effort - punching all the nails down below surface, needs a punch and smart blow. Miss one and you get to fit a new paper to the drum...

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