Keratex Hoof Hardener. The Keratex Hoof Hardener is applied directly to the horse\\\'s hoof and starts to work immediately, often showing results in just a few days. The Keratex Hoof Hardener is ideal for horses with weak, brittle, cracking hooves and those prone to sole sensitivity and loosing shoes. Hoof Hardener cross links the keratin in the horse\\\'s hoof which helps to strengthen and build healthy hooves and also promotes suppleness, flexibilty and strength in the hoof wall and sole.