We are getting so much water at the top of foundation walls that we can't get an even surface.

After we finish vibrating we seem to be floating in 1/4 to 1/2 inch of water.

Question: When we come back the next day to strip, the wall is a little uneven. We are not using wet concrete and we are not overvibrating. Are there any solutions to this problem?

Are there admixtures we can use or should we go to higher bag concrete? Is there a dewatering process of any kind?

Answer: There are several possible causes of the trouble: too harsh an aggregate, a mix that is undersanded or oversanded, too little cement, too much retarder for conditions (giving prolonged opportunity for bleeding), or use of an admixture based on hydroxylated carboxylic acid.Some measures that may help, depending on the cause of the trouble, are:

  • using a less harsh aggregate
  • increasing or decreasing the proportion of sand
  • adding a mineral admixture
  • using more cement at the same unit water content
  • using a finer cement
  • introducing entrained air if not already being used
  • introducing a water reducing admixture other than the hydroxylated carboxylic acid type if not already being used
  • reducing the amount of retardation if any
  • introducing an accelerator
  • adding a mineral admixture

Vacuum dewatering does not seem practical for this operation at the present time because equipment (other than custom-built) has not become available for this specific application. For water to be removed within a reasonable length of time it would have to be drawn out through the sides rather than the top. This would probably require drastic changes in the forming systems you use at present. It is quite possible that suitable equipment will be available at some future time.