I hired a reputable local company to install 6 foot vinyl fence around my yard. Salesman was telling me how they would be using cement to hold the post in place. To my surprise I see the workers use dry cement mix with no water or sand or anything in the holes for poles. When asked about it, they saying that "water from the ground and rain" will activate the cement and its better to do it this way than pouring wet cement. Is this correct? I even called the company and they said that this is how they are doing it for everyone.