Hey all, quick question. Does anyone know at what size/weight you need reinforced concrete with re-bar to support your spa?
There isn't a single number, it depends on the design of the deck support system and the pounds per square foot of the spa design (which is mostly a question of water depth). For wood that means how large and how close together the supporting joists and posts are. For concrete on soil it is mostly a function of the kind of soil under the slab, though for some kinds of soil the thickness of the slab and the kind of concrete used also come into it. Rebar or not only becomes a significant question if the concrete is raised above ground and thus needs to carry a load across a span. If you are dealing with concrete across a span, it is best to consult a structural engineer.