Do I cut my losses or continue? Wood Flooring

[horribleman]

In my house (75 years old) the previous owners have fastened down floorboards at right angles to the original floorboards.

Also removed a wall, so from a plan view it looks like this:
[code:1]
|--------------------|
| ..... |
| ..... |
| ..... |
| *** ------------|
| *** |
/ - Door |
----------------------
[/code:1]

and I've laid this tongue and groove hardwood flooring that comes in strips like laminate (Westco stuff) from the top to about 1/4 of the way down.

I'm starting to notice that the wood that I've laid and glued moves up and down when you walk on it.

Also, where I've got ...'s in the diagram, the floor seems to sink and then level up again as it approaches the left (front wall) and the ***s represent where the dip is most severe (approximately 23mm).

I know I should have had it screeded, but I figured I could use different levels and thickness of underlay to sort it out.

Now I'm having problems with it moving even at the bits where it dips only narrowly (less than 5mm) I'm starting to wonder if I'm going to waste my money by finishing it, and I should bite my losses (about £150) as opposed to finishing and losing about £750 worth of wood.

 

[masona]

Is the top of the floor bare wood?

 

[Pewit]

I'd suggest you should start again and lay a level subfloor underneath.

If this is not practical, then you could try the method below to take up the dips under the floor or subfloor.

You could try this solution using expanding foam. It does require you to drill small holes in the floor but this could be patched up to be almost un-noticable. It can also be used to level a subfloor using 6mm+ plywood.

1. Get a can of expanding foam with a small nozzle (there are two nozzle sizes supplied with some cans)

2. Using a wood bit to fit the nozzle, drill holes in your floor across the the area that moves - these will be used to insert the foam and to hold the floor level to prevent it lifting as the foam expands - the number of holes will depend on the size of the dip.

• 
  If underfloor is wood - don't drill into it. Check you have self tapping screws long enough to hold the new floor level for each hole then remove the screws.
  If underfloor is concrete - Switch to a masonry bit and drill through each hole into the concrete underneath enough to insert a raw-plug. Using a suitable screw to fit the raw plug, push the plug down into the concrete and test that it bites as you tighten, then remove the screws.

3. Spray some water down the holes (to help the foam expand) using a plant spray (or spray by lifting the boards if possible)

4. Place the nozzle in the hole and inject the foam (don't overdo it or your floor may bulge - practice by timing how long it takes to make a "meringue" of foam beforehand).
Then insert the screw and tighten to ensure the floor is kept level (using a spirit level). Weights may also help. If you can lift the boards you can squirt a number of "meringues" of foam in the dip area then place the boards on the foam and tighten the screws as above.

5. When the foam has dried remove the screws and repair the screw holes using coloured filler to match the floor.

Hope this helps