sentences:  Some flooring components used solely on concrete slabs consist of a dimpled rubberized or plastic layer much like bubble wrap that provide little tiny pillars for the sheet material above.These are manufactured in squares and the edges fit together like a mortise and tenon joint.Like a floor on joists not on concrete, a second sheeting underlayment layer is added with staggered joints to disperse forces that would open a joint under the stress of live loads like a person walking.