It depends on the quality of the solution being used. Ordinary quick fix solutions such as cement + ordinary chemicals can only last for a few months. While these come with a small cost, frequent waterproofing leads to a very high lifetime cost. On the other hand, products such as Asian Paints Smartcare Damp Proof are specially designed for terrace waterproofing and come with a company backed warranty of 6 years. While the initial cost might seem a bit more, the overall performance over the next few years makes it worth the investment.