Tetrion ‘Hard as Rock’ Exterior Filler sets 5 times harder than concrete within one hour, making it the perfect choice for when your project needs a strong and reliable solution for any outdoor filling jobs. It can be mixed as a standard filler or as a pourable slurry, allowing for an easy application no matter the repair at hand. Its high strength makes it suitable for filling, fixing and even anchoring. As it is designed for outdoor use it is completely waterproof when dry and the formulation is guaranteed to not sag.