Leveling Floor Part 2

Ok, I've removed my old floors, and used a laser level to get some pretty accurate measurements of the floor height.
It seems that I have a single pair of joists which bow upwards. Thus, they are 1/2" different in height than the joists on either side of them (so 1/2" in about 5'). The joists at the other side are about 1/8" lower than my target height of the room, and thus, the floor needs to be lowered in that one spot by about 3/8" of an inch. I don't want to sand the floor board down, as this would weaken the floor board to much in my opinion (the laminate flooring is running parallel to these particular joists, so I can't count on them for strength). My choices then are to raise the entire area by 1/4" (we're talking 400 square feet), or to rip off the floor boards and plane down the joists.
The problem is that the floor (BCP) is nailed down with some pretty old nails. My father lent me his 'Japanese nail-puller-outer' which is an awesome tool BTW, but about half of the nail heads actually snap off before I have the nail even 1/4" up.
So rather than pulling up 2 4x8 sheets, and all the nails involved, I'd like to cut the board right beside one of the joists, attach a 2x4 to the joist, and put a replacement board that sits on the 2x4. Hopefully that should be OK
My real issue is with the leveler though. I've never worked with the stuff before and I'm getting myself a bit nervous about it. Apparently, if you screw up with it, it's almost impossible to fix. So, the plan there is to put some screws into the floor so the heads are at the exact height I want to make the floor at each point. I then use a small amount of the leveler, and a flat straight edge to build tracks between the screws at the correct heights. I build a grid using this method, and when the grid is done, I simply pour the leveler in each square, and use the flat straight edge to level it.
I'm obviously going to do a trial before I do the final thing, but if anyone has any advice on it, I'd love to hear it. In particular, I have some nail holes in the BCP that go all the way through -- how do I keep the leveler from leaking through those, or other cracks? If one of my grids is not perfectly level, will that cause me problems (I'm aiming for less than 1/8" drop per 5'?
(Note: On top of all of this, I'm getting some pros to come in and give me estimates. If they charge an affordable price, and manage to convince me they'll do the job right, I won't be doing any of this anyway, but I'd still be interested in hearing any views/ideas for interest sake)
John
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If you have large areas that need to completely come up 1/4" then use luan board. Just use the leveler where you have slopes. Put the luan in first then you will have a frame for the leveler.
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John wrote the following:

Can you get to the joists from below (i.e. a first floor with a basement below)?
--

Bill
In Hamptonburgh, NY
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I haven't used self leveling compound, but have used non-self leveling floor filler, and set edges with thin plywood or whatever is available in the thicknesses needed and leveled the compound with an 8 foot metal straightedge (originally intended to use for cutting plywood). After drying any low rough spots can be filled with a little more filler or high spots belt sanded with a #36 grit belt (use a mask and seal off the room).
If you can get below them, the high joists can be cut to lower them and then sister in a new joist to take the load.
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Not sure if I understand correctly, so I'll throw an idea out there. It's probably the opposite of your situation, but someone may find it useful.
I had a problem in my kitchen where two adjacent joists were significantly higher than the surrounding joists. We were replacing vinyl with hardwood, so a flat floor was a requirement. As it was, pressing a 4' level flat on one side of the hump left a good 3" gap under the other side of the level.
Rather than remove the subfloor, we cut vertical slits in the joists from below. Cuts were made every 2' or so, about 75% of the way through the joist. Applying some pressure from topsides (i.e. me jumping on the floor), we 'cracked' the joists until the floor was basically flat. The next step was to sister two new joists to the existing, and the problem was solved.
Well, not quite that simple...I had to disconnect a good 50% of my electrical panel, as a good portion of the wires were running along those joists :)
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