I have an 1890's that someone had glued 1970's shag carpet to oak hardwood floors. Also had a maple hardwood floor in the kitchen with several layers of linoleum glued down with the black adhesive. After trying sanding, adhesive remover, paint stripper and scraping someone told me the solution that does work! It will sound counterintuitive but you mix a strong solution of TSP cleaner in a bucket of hot water. Then mop this solution onto the floor keeping it wet for 40 min or so. The TSP solution will turn the glue to mud which can be easily scraped off. When nothing else worked, this took care of the problem. If you leave the oak flooring wet too long, it can warp, but I used this method in 3 rooms and then was able to sand and finish and they turned out beautiful. The maple floor cleaned up beautifully as well! Attempting to sand the glue mess off the floor will fill up sandpaper sheets almost immediately - the TSP method works!!

Sorry, I completely misunderstood your post. I thought you meant a transition piece between the two floors (ie, schluter, t strip molding). Don't grout that joint between the two floors. It needs to be caulked if you go that route. Otherwise, the difference in expansion/contraction between the two materials will cause the grout to crack. As far as grout color, look at lots of pictures. I would think you'd lose a lot of the beautiful herringbone pattern if you tried to match the dominant color. The tones of the two floors are very similar, so they already connect on that level. I don't think you have an issue of transitioning in terms of grout color. I guess the more natural selection for a wood look would be a little darker than the main color, like a shadow between the boards. A lighter color or a gray will look more like a tile floor with grout. I wouldn't do something lighter, as in peachy. You can kind of see what it would look like lighter right now. The higher the contrast you have with the tile will affect how busy or pronounced the floor pattern will look. Maybe you could cut strips of colored construction paper to lay over the joints to see what appeals to you more. You've got some variation in the tile colors, but when you use a grout color that matches the flooring, the floor becomes one big solid mass of color. Here is a link that might be useful: herringbone tile pictures This post was edited by snookums2 on Thu, Aug 8, 13 at 23:15

There is a simple test that will determine if in fact you are facing the potential removal of "cutback" adhesive. Apply boiling water to a small area of the area in question. If the adhesive blisters and becomes liquified, IT IS NOT CUTBACK ADHESIVE, and can be conventionally removed. If it is not affected, IT IS CUTBACK ADHESIVE, and you'll need some special softeners and cautions to remove. Google cutback adhesive removal. The product I've used was an orange oil.

My concern is the layers of vinyl underneath the hardwood. Hardwood doesn't like sitting on vinyl and vinyl doesn't like sitting on hardwood. The two do NOT like each other. If you think this is a good idea (which it is considered on the technical side of things a horrible approach to this) then you might have to add another layer of subfloor. A nice, fat, thick 1/2" plywood to cover those two layers of vinyl. Now you can go ahead and lay the hardwood. Technically, my suggestion is hideous. It is atrocious. It is so "unprofessional" that I could weep. But if you insist on leaving the vinyl in place, then you need to think of a way to separate the vinyl from the hardwood sitting on top....and one very sure way is with plywood. Again, my suggestion is a travesty. Then again so is laying hardwood over two layers of vinyl. In the flooring world, we 'allow' ONE layer of resistant flooring (like vinyl) to sit underneath another floor. For example: the first layer of vinyl was considered "OK" to lay another layer of vinyl over top. All good. No one in the technical department batted an eye. If a THIRD vinyl floor was proposed (or a laminate, or linoleum, or cork, or hardwood, or tile, or even carpet) it would be a "NOOOOOOOO! STOOOOOP! DON'T DO IT!" type of answer. So I will officially say: No. Stop. Don't do it. There. It has been said. That being said, if you as the homeowner choose to forgo the installation instructions and the "Best Practices" as set out by the National Wood Flooring Association (as homeowners your word is "law" when it comes to things like this), you are welcome to go ahead and lay hardwood over two layers of vinyl. If you do it, I suggest a new layer of plywood to help things along - because you need FLAT. And most "old hardwoods with two layers of vinyl sitting on them" are anything but flat. Good luck. You would be better off remediating the asbestos/vinyl and getting down to bare hardwood. Now a new floor (with the help of a layer of plywood) can go down. Or you remove the original hardwood with the vinyl (this is easier to do than scrape off the vinyl...and easier = cheaper) and start with a new layer of subfloor and go after it like it should be done. But as homeowner your word is "law". If you tell a professional to "just do it", they will say "yes ma'am/sir" and do it. But they will not warranty their work. You will be left holding the bag - and all the pit vipers that lay inside. It's your call.