Look at any parking lot or other mass concrete poured in sections
on different days. There will probably be one section that is
snow white, or at least substantially more white than all the rest
of the concrete. That section was rained on the same day it was
poured.

I cannot give you any science for the result, but I can sure show
examples. This difference easily lasts 10 years or more, though
it gets less noticeable with time as the oil stains and other
discolorations take over.
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)




wrote in message
oups.com...
The only hand-mixed cement question I have involves color. Is
there an
additive to get hand (bag or portland-sand-stone) mix to bleach
out?
The ready-mix always bleaches to a nice bright white. I used to
do
concrete work for a contractor, and I would often be the one
stripping
forms and wetting the setting concrete. I have never been able
to
duplicate the nice bleaching with a bag mix.