The Sika Fence Post Mix is a two-component, pre-proportioned polyurethane resin that comes in a lightweight pouch-like bag. Mixed in the unopened bag and poured into the hole around the fence post, those components reportedly produce a fast-expanding foam that fills up the hole then hardens to fully set the post within 2-hours' time. One 33 fluid-ounce Sika Mix pouch is designed to replace two 50-pound bags of concrete, and no water or special tools are needed.