I have an existing slab I am tying a 8x13 closet slab to in North Texas.

Up until yesterday, I was going to drill 9-12" into the existing foundation every 12", epoxy some rebar into the holes, and pour right up next to the existing foundation.

A guy got into my head yesterday telling me I need to use slick rod and grease so the new foundation can move in and out at the joint. I think he is using an expansion joint philosophy from a side walk or driveway, but I thought I would ask:

What do you guys suggest? Tie it in and pour right next to it, or use slick rod and an expansion material?

Any help will be greatly appreciated.

BB