The one-year warranty on my new home is about to expire. I had noticed a few hollow spots and decided to spot check for more. That light spot check found 60 problem areas. I'm guessing there are at least 100 in 1500 square feet. Is it reasonable to expect the builder to rip up and replace the whole floor? I also suspect the substrate is not level. How do I prove that?

Not without giving them the opportunity to repair it first. 100 hollow spots and you are just now saying something? if you have that many you have some real issues.

I take it this is a glue down hardwood floor over concrete? Hope so becuase it's difficult at best to tell over a wood substrate. What sounds hollow to you may not seem hollow to others.
And besides that, whats the extent of hollowness? Is a six inch spot going to effect the intergrity of the floor as much as a 3 foot square area?

Here's the latest: The builder sent their floor people to look at it. Both the initial repairman and his supervisor agreed that the floor needed to be replaced. Now the issue goes back to the manufacturer who sends a certified wood flooring inspector to find out what the problem is.

The floor slopes to such a degree that a furniture installers who had to level a new china cabinet commented on how excessive it was.

How do you fix a sloped floor? It's been that way since we moved in. I don't think it's the foundation, I think its the substrate.

And, yes, it's engineered hardwoods glued down over concrete. They are small spots in out of the way areas in a large home, which may explain why we initially only noticed 10.

You need to get the flooring installer, the builder, the supplier and the manufacture of the floor and glue to agree where the problem is or they will all point the finger at each other. Sounds like a bunch of low spots in the slab but it could be many other things. Its pretty easy to find out how level the floor is all you need is a long straight edge and start laying it around the floor and look for gaps underneath. manufactures require no more than 3/16' in 10' normally. The trowel is normally 3/16" to 1/4" so one can see why it needs to be that flat otherwise the boards just bridge the void/low spot and never get into the adhesive resulting in hollow or loose spots.

KevinD, that makes sense. We're definitely over 3/16 in 10 feet. Is that fixable? Do they repour concrete?

The grade of the floor (slope or level) has nothing to do with how flat the floor is. Key word is flat. Thats the builders and concrete contractors problem.

Unless the low spot is severe you cannot say it's out an eighth of an inch or what have you when the surface is covered with glue and wood. The wood could have a bow in it causing it to lift out of the adhesive. So essentially to be certain you need to rip out the floor and check the substrate without anything on top of it.

That is 3/16 in 10 for the subfloor, but check your building codes for finished floor flatness, to see if it even meets code.
Here it is 1/4 in 10.

Hollow areas are a big problem for those that forget to add in the floor prep, because they are afraid they are going to get outbid by the cheap guy. In the end, they end up being the cheap guy... for a reason.

Sorry to confuse you , the guys are right those specs are for the subfloor prior to installation. Level is a bad choice of wording flat is more appropriate. Thanks for help clarifying.

Yesterday the home builder's representative and the installation company came to assess the situation. Of course, the installation company said it was a wood or adhesive issue, not sure which. Either the individual pieces of 5-inch plank are separating (apparently it's some kind of colored piece glued over poplar) or the adhesive didn't work.

The wood manufacturer is sending an independent certified wood flooring inspector.

BIG QUESTION: How many hollow spots does he have to find before the whole floor is replaced? These two guys were acting like injected glue would solve everything. I would like the whole floor replaced. If the inspector finds 150 problem spots today, who's to say that a year from now I won't find 150 more?

Is there an industry standard for a total loss?

There's a multitude of reasons for glue not sticking.

Improper floor prep, some say CSP-2 to 3, ie to smooth and or reflective
High moisture vapor emission rate
Wrong trowel
Wrong adhesive
Not rolling
Bowed planks
Skinned over adhesive
Dusty surface
Contaminants on slab surface like bond breakers; paint, sealers etc
Dewpoint
No heat or HVAC going
No accliamation period
......................................yata yata yata

Most of what Stephen just listed are installer errors. As for the amount of hollow spots I am not sure but some manufactures state more the 10% defective boards warrant a full replacement. If you sub floor is as uneven as you are saying the only proper way to fix it is to rip up completely and flatten it with either leveler, grinding, or both.

Drill and fill is an industry accepted correction for hollow areas.
The problem lies with prefinished wood and a thoughtless installer, drilling directly in the center of the board to inject adhesive, instead of the joint intersection, to hide it easily.

I inspected a new home that had had 700 injections and still had hollow sounding areas. Mickey Moore, has a PHD in wood science and contributes to FCI magazine states that hollow sounds are not a reason to fail a floor unless they have movement. Those areas can be remediated by injecting Dri TAC and allowing to dry overnite. Tap on ceramic tiles and most likely you will find hollow spots. Drop something on them and they will crack or break. Advised this client to get several boxes from his builder for his ceramic tile and don't forget the grout.

That's pretty much what the inspector told me! I'm concerned about trying to sell a high-dollar home with floors like that.