The World Trade Center memorial (WTC) in New York City contains two enormous fountains which presented many waterproofing challenges. 

The contractor team spent over 18 months installing the concrete waterproofing system that was selected for the job. Here are the methods utilized:

When designers started to plan what would become North America’s largest man-made waterfalls (World Trade Center Memorial -WTC) in New York City, they faced a number of challenges. One of the biggest concerns was how to contain vast quantities of water while preventing infiltration into underground structures.  

Polyurethanes are used to make products with properties ranging from soft flexible foams such as memory foam mattresses, to rigid foams used for house insulation. They can be made into soft rubber as used for skateboard wheels or into very hard enamels as used in modern automobile paints.

 The range of properties can be quite wide, just by changing the chemistry a little, but there's a problem. The traditional chemistry uses materials that have an affinity for water. For applications such as fountains, pond liners, waterproofing, water and waste water tanks, roofing — where long term or constant immersion is an essential requirement — that affinity for water will lead, eventually, to the product swelling or even failing. The reason is in the chemistry, itself. Here’s why.