With cold weather concreting operations it is important to remember the possible serious consequences of exposing fresh concrete to concentrations of carbon dioxide caused by heating devices which exhaust flue gases into closed rooms. This subject was throughly covered in a paper entitled "Effect of Carbon Dioxide on Fresh Concrete" written by J. A. Kauer and R. L. Freeman of the Huron Portland Cement Company. In their paper, they suggest the following ways to prevent carbonation damage to floors placed during cold weather: a) use temporary heaters which do not allow combustion gases to contaminate the air; b) use a membrane curing agent if unvented heaters must be used making sure the surface is completely sealed; c) if salamanders or unvented heaters are used, provide proper stacking to exhaust combustion gases to the outside.