When dealing with an abscess, there are two ways of treating it. First you should always clean and inspect the hoof to make sure there are no other objects (rocks, manure etc..).  At that point, brush the hoof clean with a wire or stiff brush.  If the horse is going back to a clean stall, apply the Clay and simply put your equine friend away.  If your horse is going back out to a questionable environment, you can use a hoof boot or a duct tape boot to cover the hoof. In addition, I like the use of plastic wrap or vet wrap to help speed up the process.