Make sure the cement surface of your bare floor is fully sealed with cement sealant. Follow the package instructions on your cement sealant and allow at least 24 hours in dry conditions before proceeding to the sprung floor installation.
Install the CBX grade plywood first. Use a lower grade of plywood for the first layer of your sprung dance floor. The first layer needs to be durable but it does not need to be pretty, so knotted pine is an inexpensive choice. Secure the first plywood layer with construction glue.
Use a band saw to cut EVA foam rubber into blocks, approximately 4 inches high by 6 inches wide by 4 inches deep. Space the blocks roughly 10 inches apart on top of the plywood layer, making sure to place most blocks on top of edges and joins, which will reinforce the structure of the sprung floor and prevent cracking and splitting. Secure the blocks in place with construction glue and allow to set and dry completely.
Install the top layer of the sprung floor last. Use a higher-grade plywood to maximize the attractiveness of the floor. If you will be using the sprung floor for percussive dance, which damages most indoor surfaces, use square panels of cheaper plywood instead, which you later can paint black to conceal imperfections.
Lay the plywood perpendicular to the first layer of the floor. For example, if your first layer of plywood was installed in the room right to left, install the top layer of plywood from top to bottom. This is essential to maximize the floor's flexibility.
Secure the top layer of the sprung floor to the EVA foam blocks with wood screws. Use wood filler in a shade similar to the top layer of plywood to fill in any cracks or gaps.
Sand the surface of your sprung floor and sweep or vacuum the dust. Once the sealants have set and dried completely, mop the floor to get rid of any remaining residue. You can paint the surface of the sprung floor if you wish once it is completely dry.