The questions answered here were collected by the editors and submitted to Harald Wenander, Technical Director, Tremix AB, Skarholmen, Sweden. Mr. Wenander has answered most of them himself but reports that some replies were written in cooperation with Professor Roman Malinowski, of Chalmers University of Technology, Gottenburg, Sweden. A sample of the question follows. How many workers are there to a crew for vacuum dewatering of concrete? The system requires two men to place the suction mats or pads; but once this is done and the vacuum valve to the pump is opened, the vacuum treatment continues on its own for the 15 to 20 minutes of operation. The pump needs no supervision. Should the tank become overfilled with water the pump stops automatically. What is the largest size mat in use? Our company's largest standard mat is about 400 square feet, though larger sizes have been used successfully for special jobs. The largest one we know of is about 550 square feet. What is the smallest size job on which vacuum dewatering is practical? There really is no lower limit; almost any size job can be tackled. Can admixtures be used in concrete to vacuum dewatered? Yes, but they are often unnecessary. The only admixtures with which special care must be taken are air entraining agents. The fine air bubbles they produce tend to slow the rate at which water can be extracted. No more air entraining agent should be used than the amount needed for a total air content of about 4 percent in the original mix.