How to Finish a Basement With Floating Slab Floors

Sweep the unfinished basement floor to remove accumulated dirt, dust and debris. Unroll underlayment over the cleaned surface, rolling it in sheets that overlap each other at the edges by 3 inches. Tape the edges of sheets. Cut the foam underlayment to fit around the edges of the basement floor using a utility knife.

Lay the first or starter course along the longest, straightest wall in the basement, with their grooved sides facing the wall. Space the planks in this course 1/4 inch away from the wall, and place plastic spacers between the wall and boards to create an expansion gap. Cut the last board to fit the available space on the floor, maintaining the 1/4-inch gap between its end and the adjacent wall, using a handsaw.

Start the second course with the half plank from the previous course to ensure the lines do not match up. Slide the grooved sides of the planks in this course into the tongue sides of the planks in the previous course to secure them together. Repeat this process to lay the remaining courses of flooring planks, until you reach the last course.

Trim the tongue sides of the planks for the last course of flooring planks so they fit the available space. Maintain a 1/4-inch gap between the planks and the adjacent walls.

Measure and cut flooring trim to install around the perimeter of the floor. Set the trim against the wall, flush above the flooring planks, and nail it to the adjacent wall using trim nails. Ensure the trim covers the exposed expansion gap between the edge of the flooring planks and the wall. Repeat this process to install floor trim around the basement.