Q: I’ve heard about the “Deck Growth” phenomenon associated with grid reinforced concrete decks. What is it and do I need to worry about it? A: Deck growth is a phenomenon associated with flush filled, unprotected grid reinforced concrete decks. Without an overlay, corrosive brine infiltrates the concrete and grid interface and attacks the steel grid forming rust. After many years of service, the rust propagates and expands. But because the concrete is contained within the walls of the grid, it is effectively compressed resulting in a net expansion of the deck. The standard reinforced concrete deck also experienced problems using rebar without a protective coating. Upon oxidation of the rebar, the rust would expand causing extensive cracking and spalling. Once the industry began using rebar with an applied corrosion protection, the problem has essentially been eliminated. Now that most grid decks are galvanized prior to receiving concrete and an integral concrete overfill is required, the problem of deck growth is avoided.