Q: In our part of the country we don't have much trouble with rain. However, we have a project coming up that must proceed on schedule and we are concerned about what might happen if we should ever have to shut down on account of rain. Are there any standard practices for proceeding with concreting in rainy weather?

A: Placing concrete in the rain should ordinarily be avoided, but if concreting is absolutely necessary all precautions should be taken to keep additional water from the fresh concrete.

Following are some measures recommended by Robert F. Adams in Concrete Construction Handbook, edited by Joseph J. Waddell:

  • Cover the working area with tarpaulins or other protection.
  • Use lower-slump concrete than otherwise (since evaporation practically stops during a rain).
  • Before placing concrete on footings or on construction joints, dry up any puddles of water already standing on them.
  • Provide a location for water to drain off the top surface, and try to maintain a slight slope on the fresh concrete surface if possible so that bleed water will move toward the drainage point.
  • Avoid working the surface of the fresh concrete.
  • During thunderstorms of short duration, stop placing concrete until the storm passes but meanwhile cover the concrete with tarpaulins, plastic sheets, or other effective protection.
  • If rain is so heavy that puddles cannot be removed and the concrete is being washed, it may be advisable to suspend concrete placing. If so, bulkheads, dowels, headers or steps should be put in so that the concrete already placed is left in the best condition possible for continuing the work at a later time. This process creates a construction joint and when work is continued the cleanup practices normally recommended at construction joints should be followed.