Absolutely not! It is absolutely certain that water will get under the tile. That is precisely why there are so many problems with outdoor tile decks. People THINK - and are even misled to believe - that a tile installation is waterproof and therefore they don't pay too much attention to the proper waterproof treatment underneath. The failures are often waterproofing failures where leaks that have been happening undiscovered for years eventually cause rot requiring major renovation work. In these situations, not only does the structure need replacement work, the tile application must be torn up to get at it. The water will most likely enter through cracked grout joints or on the perimeters. If the tile cracks, water will enter. If the deck is in a cold climate, the moisture freezes, expands, and may cause tiles to erupt. With Tiledek, a failure at the tile surface doesn't mean the waterproofing system has failed. If the membrane is intact and performing its function of keeping the water out, replacing a cracked or erupted tile or a cracked grout joint is relatively easy and inexpensive.