I just installed 5" Shaw Epic engineered hardwood, glued on with Bruce adhesive on my concrete slab. I spent a lot of time leveling the subfloor, and did a pretty good job (I have installed glue-down hardwood in the house previously). Unfortunately, I checked the floor over 6'/8' lengths, but must have missed an overall crown in the floor.

Now that everything has dried, the last ~6 inches of many of the planks at each wall are not bonded (i.e. sound hollow when tapped, and in some cases physically flex down). I'd ignore it based on the fact that it is at the edges, except that we are planning to place a large 4-leg desk against the wall, and two of the legs will likely be on the void of the planks; I am worried that it will damage those planks, or (worse) leverage the center of the floor loose. Changing where we put the desk would cause significant marital strife.

I looked at the DriTac void filling system, but 1) it is pricey, and 2) it seems like would run right out of the void since there is a large open edge.

I've pondered injecting adhesive under the floor via the expansion space, either using a caulk gun with Liquid Nails subfloor adhesive (claims to fill a 3/8" gap), or more Bruce adhesive (but I have no idea how I would inject it).

Does either of those ideas have merit? Anything else that people would suggest?

I'm not sure it helps, but here is a picture (the offending wall is on the right hand side): http://twitpic.com/1mta87

I can walk into any gluedown installation and find at least one hollow spot, next to the wall.

The wall line is the hardest place to prep perfect.

Spending $70 on a Dri-Tac kit is expensive?

I bet you could re-sell the kit and what glue you don't use, on craigslist or even e-bay.

Go to any horse tack & feed store, pick up a large horse syringe for a buck, inject the adhesive.