Hardwood Floor Help Needed

Hello,
I have a 1920s house I am remodelling and got to the floor phase. Decided for hardwood. Problem is that the upper floor sagged about 1/2in (in the center) over the years and I cannot push the floor back up.
The hardwood planks are about 5/8in thick and 3in wide.
Right now I am considering two options.
1) get laminated wood in several different thicknesses, cut strips and screw them to the old floor trying to eliminate or, at least, reduce the sagging to a minimum and then nail the hardwood planks to them.
2) pour self-leveling compound and then glue the hardwood planks to the cement, as suggested by a friend, but I am not very fond of this method.
Anybody has experience with this problem and how it was solved?
Thanks in advance!
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Presumably you have floor boards on joists and it's the joists that are curved.
Bolt straight joists to the sides of each curved joist.
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On May 1, 4:09 pm, "CWatters"

Cannot bring the joists up (straighten them) because that would mean pushing the walls, ergo the ceiling and roof, also up. The sag is controlled by new beams and columns so the floor will not sag anylonger.
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No you misunderstand my suggestion. You don't try to move or straighten the existing joists. You just add sister joists along side. Drill through both and bolt together. The sister joist will stand 1/2" above the old one in the middle and flush at the walls. Fix new floor to flat sister joists.
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Sketch here...
http://img222.imageshack.us/img222/5198/sisterjoistmr0.jpg
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On May 2, 3:19 am, "CWatters"

I was assuming the floor sheathing was in place. Obviously, you don't want to remove and replace it for your fix. If for some reason it isn't, I would suggest shimming the top of the bad joists would be easier than bolting on a sister.
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On May 2, 1:19 am, "CWatters"

Thanks much! However the subfloor is already in place and removing it would be a major headache, besides the project delay. Whatever I do must be over the existing subfloor.
I can try to replicate "dummy joists" over the existing subfloor and nail/glue a laminated wood new "subfloor" over them. That will take a lot of work but is likely faster than removing the old one.
Gluing the hardwood planks over self leveling cement seems to be the easiest/fastest route but I do not know if it can be done without risking damaging the hardwood planks or making the floor squeaky.
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says...

It would be a much greater project delay if you have to rip up all of the new hardwood flooring because it failed. The only solution that has been offered to you that is fail safe is using sister joists.
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Of course you realize that to sister joists, he would have to remove all the partitions, all the subfloor, sister joists, redeck, reframe partitions, drywall etc or he risks floor failure (which would be what--a few squeaks?) . This is not a realistic approach to fixing a 1/2" dip in a floor.
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says...

He would only have to remove that part of the subfloor that is sunken.
Do you know for a fact that he can glue 5/8" thick hardwood flooring to leveling cement? That's what he is proposing. Hardwood flooring moves a helluva lot.
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Another problem with sistering joists is that there could well be wires crossing the joists, it being a second floor and all. Have to move the wire or notch the new joist somehow. Also, there could be bridging and blocking you'd have to remove--yet more work. Also, the OP is talking about eliminating the sag near doors. So you are suggesting he rip the subfloor around partitions, under doors, and somehow sister new joists in these areas?
You can glue hardwood to concrete. I've seen it on directions for 3/4" strip hardwood flooring. I haven't done it, so I'm not going to suggest it, and the OP seemed resistant to the idea anyway. If it was mine(and I underwent a personality change so I couldn't stand leaving it a sag in a floor in a 100 year old house) I'd cut some shims to flatten, screed in some webcrete floor leveler between the shims, and staple the floor through the shims. Most places it'd probably work to staple right through the leveling compound anyway.
Also regarding "self leveling compound", I don't know of a floor leveler that is actually self leveling. That is, you can't stand in the middle of a room and dump it from a bucket and VOILA it's level. you need to get down on your hands and knees and work it. In your case, you'd probably want a long straight edge to sort of screed it.
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says...

Yes. The sister joists have no need to be load bearing joists. They would be put there for the sole purpose of raising the floor back to level. They can be 2"X4"s and can even be cut in sections to fit around wires, etc. Seems like a 10 to 20 hour job to me. If were my house and I felt that the floor had to be level (which I wouldn't) that is the way I would go. That way there would be no future concerns of loosened flooring or buckling.

Sounds reasonable to me.

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>

This site suggests it might be possible to lay decorative cement over wood but recommends applying "metal lath or diamond back mesh with a staple gun or staple hammer first.
I still don't like the idea though.
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http://www.concreteideas.com/concrete_ideas/interior_floors/concrete_overlays_and_resurfacing/decorative_concrete_overlays_over_a_wood_substrate
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Regarding option one, I'm skeptical of the practicality of that. How would you decide what thickness where? Wouldn't the thickness have to vary on at least some of the strips. I've thought before of screwing down a 2x2 and snapping a line at level, and then removing the strip, sawing it, and reapplying it. Sounds like a ton of work. I think you would have to fill the spaces between the shims with floor fill or something. Liable to get a lot of squeaks.
There have been other posters on this group who have inquired about nailing hardwood down over self-leveling compound. Not sure how it turned out, but I really think that it might be the way to go.
The option you don't list is leaving the floor as it is. It is a 90 year old house after all. Part of the character of an old house is dips in the floors IMO.
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I thought about leaving as is but it would look really terrible. I can live with minimizing the sag but have to eliminate it at least where the doors are. I tought about getting different laminate thicknesses and nail/screw them over the wood strips of different thicknesses.
That would give me a relatively flat surface to nail the hardwood planks to. It is a lot of work indeed, ergo the questions about laying cement leveler and gluing the hardwood planks instead of nailing them.
How does glue work with hardwood floor meant to be nailed? What could be the problems coming out of doing so?
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Look into the possibility of using a self-leveling floor compound to improve level on the subflooring. This would be a thin layer of concrete, in effect, that would shim the difference you need. Nailing through it might be a trick, but given the thickness, probably not. Anyway, it's just an idea, and potentially an easy solution.

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The sister joist is the only sure and sensible fix. No need to thank for suggestions since your not using any of them anyway
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