I found a few small hollow pockets under some old tile. I'm adding new tile that will butt up to them to complete the floor. I was thinking of putting Devcon 2-ton epoxy into a syringe and injecting it into the mortar gaps that should lead to those empty pockets. My goal is to adhere it and put something solid under those spots. Anyone every try this? I hate to have those tiles break later due to being unsupported. Thanks.