So I did a fair amount of research on this product and watched a few YouTube videos. I see the reviews are mixed and I don't understand why. Backstory: I recently remodeled our kitchen laying down 12x24 tile which comes with a curvature in the middle from the manufacturing process. I've never laid this size tile before so needless to say it fought me pretty hard especially because our sub floor was far from level. I did my best to ensure I left no air pockets while I installed them. While walking one day I heard a loud pop and nearly puked, I dropped to the floor and saw the grout was separating from the tile. So I began knocking on all of each tile to discover 3 tiles with hollow centers. Of course the affected tiles are in the center of the room and thought after all that work I now have to start carving out tile. I frantically began googling and found this product. On to the install, firstly, you need to take the time to determine where the air pocket is, locate the most likely path from the grout line to the air pocket. I then drilled the two holes into the grout (as the instructions state) and began pumping the adhesive. I found after a bit it began coming out of the install hole and not the second hole, meaning it wasn't getting everywhere it needed to within the air pocket. I drilled a third hole and pumped more, eventually it began seeping out of the third hole, success. The most important thing is that you are careful when you drill so as not to penetrate the subfloor or you'll just be dropping adhesive right through into your crawl or basement. The best way to avoid this is to take your drill bit and mark the depth from a spare piece of your tile, I used painters tape. I put a buddy bucket filled with water on the tile for 24hrs and now it's solid as a rock. I cannot say enough about this product, it can be a messy process but cleans up easily and is a small price to pay for such a miracle. I know this was long but I know I wanted to know as much as possible about it before I tried. I hope this helped.

I had some hollow tiles. This worked as claimed, but it is messy. I took somebody else's advice and warmed the tubes up before use. Shook them well to mix up the contents. Worked it into the holes I made slowly, but still had leakage at the back of the tube. It made a heck of a mess, but I don't care cause it worked. Cleaned well with a wet rag. Two 10 ounce tubes took care of four 12x12 inch tiles. I ended up buying another set cause i found another hollow tile. Home depot has it in stock, but it's $15 a tube and definitely not worth the hassle for the 40 mile drive.

I tested it on one end of a wood plank tile and it seemed to work well, so I proceeded to glue a few more that sounded hollow. 24 hours later at 65 degrees in the room and it is still runny and white.
I've seen several mentions of shaking the tube before applying. If this product can separate over time resulting in the inability to cure/dry in the stated time then the directions need to state that it needs to be shaken. Will turn up the heat in the slab and see if I can get it to cure.

Update 10/2022: Porcelain tile on a concrete floor at 68 degrees room temp and 45% RH and it took 5 days to completely cure and turn clear. Thought maybe I had a bad tube so ordered more and shook it for 10 minutes first. Same results. I let it drip onto a paper towel when moving between tile and that is drying at the same rate where the larger puddle is. What I've observed is that in places it is very thin it dries quickly, but it you fill the mortar cavity it skins over and then takes days to fully cure.

After getting a $25,000 quote to replace the failed tile floor in our house, I decided to give this product a try. I'm very pleased with the results, but one needs to follow closely the directions.

My Insights into the product:

Although it comes in caulk tubes and uses a caulking gun, it's NOT caulk; be ready for a completely different product. It's consistency is very thin, so keep plenty of wet disposable towels handy to wipe up drips and excess after injecting.

Be sure to shake each tube before use.

Unscrew the applicator tip, puncture the tip of the tube, then screw on the applicator tip and cut to size.
Finding the "right" areas to drill takes a bit of practice....I use the "tap" method and listen for a hollow sound to not only find the treatment area, but to find the best spots on the grout lines for drilling. you MUST drill into an air gap so the product will inject and spread.

Use a masonry bit on your drill and go far enough to get through the grout line, just to the air pocket below.
you will need to cut the applicator tip to match the drill size....I used a 1/8" bit...plenty large enough to apply the adhesive.

Keep a small hand vac handy to clean out ground dust and pieces from each hole.

Press firm enough to seal the applicator tip to the hole, then squeeze the caulk gun handle slowly and smoothly to apply the product.

Weigh down each treated tile with a full paint can or bucket with water and leave weighted for a full 24 hrs.

I'm averaging 1 tube per 18" tile....so far I've fixed the floor in 1 guest room, the hall and hall bath. Even though this will take some time, it's a much better alternative than spending Thousands and emptying half the house.

Having problems with delamination of top layer of my engineered wood floor (due to its age, or poor original adhesive, etc.) I used to remove each bad plank, clean it, trimmed it as needed and then glued it back: very time consuming and often poorly looking because the thin top layer plank could crack or break during the process. Using Fix-A-Floor takes minutes to repair it! Just make sure put heavy weight, 30 Lbs or more, on top of the repaired floor, I recommend for no less than 2 days