Abstract: A method to remove a depression in a floor extending on top of a supporting underfloor and to prevent recurrence of this depression thereafter, the method comprising: a) determining the pressure that the floor may withstand in use; b) preloading the floor by exerting onto the depression in the floor a pressure at least equal to the pressure determined in step (a), using, for example, dead weights to do so; c) injecting an expandable polymeric foam in an unexpanded state beneath the depression in the preloaded floor between this floor and the supporting underfloor and allowing the foam to expand and level the floor until the depression is removed; and d) releasing the pressure exerted onto the floor after the depression is removed. The pressure exerted onto the floor in step (b) exerts a compressive strength to both the foam injected beneath the floor and the supporting underfloor.