People often tell us they have heard or were being told to use Elastomeric because it's waterproof. This may be true, but it is not a universal truth and should not be used as a default spec, as it seems to be lately. Often times, it is easier to just say use Elastomeric and that should protect everyone involved, but be careful. The following article is a bit detailed, but illustrates the need to do some homework before defaulting to Elastomeric.
Denver Commercial Coatings: Industrial, Hotel, Retail, Office, HOA, Parking---Interior & Exterior