nokostya Oct 4, 2011:

http://www.fhwa.dot.gov/infrastructure/materialsgr Storage of Cement. Portland cement is a moisture-sensitive material; if kept dry, it will retain its quality indefinitely. When stored in contact with damp air or moisture, portland cement will set more slowly and has less strength than portland cement that is kept dry.

Bourth (X) Oct 4, 2011:

go off Kashew's "go off" is good because it's nicely ambiguous, and the French is not clear to me. It appears to be saying that the slightest moisture will make cement set, but this is not true. Cement which is stored in damp conditions (but is not wet) will subsequently take longer to set (it's as if it's been vaccinated against water by homeopathic doses) and will not attain its theoretical strength.

"Go off" has the deal senses of "setting" (going hard and strong) and "deteriorating", as fruit or meat "goes off" if not stored correctly.

More context might help us pin down precisely what they mean to say.