Shotcrete gunned on overhead surfaces such as tunnel linings must have a fast initial set. Otherwise, it doesn't stick. Until recently, only dry-mix shotcreting combined fast setting with high early strengths needed for many applications. But dry-mix shotcreting subjects workers to dust and 35 to 70 percent rebound. Wet-mix shotcreting eliminates dust and reduces rebound, but it also reduces strength. Sodium silicate, the liquid accelerator commonly used for wet-mix shotcreting, speeds only the initial set. It reduces strength at age one day or more and can reduce 28-day strength by up to 50 percent. Now a liquid admixture based on potassium aluminate makes wet shotcrete set rapidly without losing early strength. It reduces 28-day strength by only 10 to 20 percent. And it allows workers to place 12-inch-thick shotcrete on overhead surfaces in one pass with less than 10 percent rebound.