from the ikeafans archive:

"Our island sits over a floating floor which is over the plywood subfloor (basement underneath). The space underneath the island came out to exactly the height of three 2x4's stacked on their sides plus one piece of 1/2" plywood. Near each end of the island (two 30" base cabs) we had a stack of these pieces cut about 12" long. The first 2x4 was screwed into the floor using 3" deck screws. The second and third pieces were screwed down on top of the first, then the plywood was attached with some shorter screws. We placed the island where we had marked previously, and drove screws down into the stacked wood from inside the cabinets. It's pretty solid now. "

I realize you are securing to a slab but the same principle applies. This is how I always secure island/peninsula cabinets to the floor, as it allows you to still use the legs and toekicks. Good Luck!

Screwing through a "floating" floor violates the floor manufacturer's installation instructions.

lgteacher:

Is your kitchen on a slab, crawlspace, or basement? What type of floor do you have?

This post was edited by Trebruchet on Sat, Jan 3, 15 at 20:18

My floor is concrete slab. I have an engineered hardwood floor over that, which is about 1/4 inch thick. It is over 20 years old, and glued down, not floating. From what I read, I will use tapcon concrete anchors to fasten the 2x4 cleats.

I would use construction adhesive between the floor and the 2x4 after cleaning the floor with acetone in addition to the Tapcons. I'd reinforce the cabinet connections with screws too.