Achieving the greatest potential possible through the use of site-cast concrete involves, among other things, a willingness to use every possible avenue in learning more about this medium. This may include the de-bunking of some favorite theories. Fallacy one: air content of 5 to 6 percent should be used for optimum durability. Since air content is measured by the volume of air bubbles in relation to the total cement paste matrix in a given quantity of concrete, the total matrix volume will be the deciding factor in establishing optimum air content. Cement paste volume is dictated mainly by the maximum size aggregate used, although aggregate gradation will also have an influence on this matter. This is an inverse proportion- the larger the maximum size aggregate, the smaller will be the cement paste volume. As a result, optimum air content in a grout, for example, would be many times that required for concrete to be used in, say, a dam. Fallacy two: five foot spacing of support bars for all top steel is adequate. Although the recommendations of the Concrete Reinforcing Steel Institute permit standard spacing of 5 feet between support bars for top steel, it is best to recognize some qualifications of this rule in actual job practice. The effect of top steel varies considerably. For example, even if top steel is only one-half of an inch below the level specified on plans in a 4 inch slab, this would result in a 16 percent loss in distance of the steel from the soffit. Fallacy three: sugar always delays or prevents concrete hardening. While this is true it should also be remembered that very large amounts of sugar can result in flash set. Finally, fallacy four: concrete should be discharged at an angle into high vertical forms to break its free fall. Some contractors discharge concrete into high forms on an angle to prevent segregation. In reality, this only aggravates it.