Styrofoam doesn't absorb very much water. Marinas here use big blocks of styrofoam with concrete poured on top to make the wharves and walkways between boats. They have done this for many years, and I have never worried that one would sink while I was walking to my sailboat. -- Diane Whitehead Victoria, British Columbia, Canada maritime zone 8 cool mediterranean climate (dry summer, rainy winter - 68 cm annually) sandy soil