The curing of portland cement is a chemical process that allows the strength
to develop, and at the same time the water tightness. Curing occurs with
moisture and temperature, so the concrete or mortar needs to be kept damp
with some form of covering to continue the curing. For applications like
ponds, the minimum curing time would be about 28 days with a minimum
temperature of 50 degrees F. After the moist part of the curing, the
concrete should be allowed to dry for about a week to evaporate some of the
water out of the pores. This will retard the movement of the calcium
hydroxide in the pore water, which is what causes the high pH of concrete.
While dry, carbon dioxide in the atmosphere will react with the calcium
hydroxide making calcium carbonate, limestone, in the outer pores, improving
the water tightness of the concrete. Then turn on the waterfall and monitor
pH. If the pH starts to increase, turn off the waterfall and allow to dry
again.
--
RichToyBox
http://www.geocities.com/richtoybox/pondintro.html


"Gideon Singer" wrote in message
...
I am in the process of building a water fall for my pond which has
fish in it. I know you need to cure the cement before you can allow
water to flow over it into the pond. How long does the curing process
need to be before it is no longer a danger to the fish?
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